Testing fabric color fastness with gray cards is a fundamental and crucial evaluation method in the textile industry. It primarily serves to objectively assess the degree of color change in textiles after undergoing tests such as rubbing, washing, perspiration exposure, and light exposure, as well as the potential for color transfer to adjacent fabrics.

1. What is Fabric Color Fastness?

Colored fabrics during production or garments made from them during use are subjected to various external environmental factors. The ability to resist these external forces is termed the colorfastness property of the fabric or garment.

2. What is Fabric Discoloration?

In dyed textiles, environmental factors can cause fiber color loss, destruction of dye chromophores, or generation of new chromophores. This leads to changes in color saturation, hue, and brightness.

3. What is fabric color migration?

This refers to the phenomenon where, under various environmental influences, dyes detach from the originally coated fibers and transfer to other fabrics, causing them to become stained.

During colorfastness gray scale grading, discoloration and migration gray scales are used to evaluate colorfastness. Currently used gray scales include AATCC, ISO, JIS, and Chinese National Standard GB gray scales. Each gray scale has slightly different gray levels.

4.How to Use Gray Scales to Test Fabric Color Fastness

4.1 Discoloration Gray Scale: Used to evaluate changes in the test sample's own color. It consists of 5 pairs of small gray cards, ranging from Level 5 to Level 1.

Level 5 indicates no change at all, while Level 1 indicates the most severe change. Within each pair, the left card is a fixed neutral gray, and the right card gradually lightens in shade, representing the degree of color change.

4.2 Dye Transfer Gray Cards: Used to evaluate the degree of color transfer from the test sample to an adjacent white fabric (commonly called the backing fabric). Consists of 5 pairs of small white and gray cards, ranging from Level 5 to Level 1.

Level 5 indicates no color transfer whatsoever, while Level 1 indicates the most severe color transfer. In each pair, the left card is a fixed white, and the right card is a progressively darker gray, representing the degree of color transfer.

5. Color Fastness Gray Scale Evaluation Method

Grading Scale Table

Masking Card

(As shown above), during grading, specially designed apertures are used to mask sample cards for evaluating multi-fiber fabric staining, rubbing colorfastness staining, and general staining assessment.

Using masking cards allows better focus on the sample being graded while covering other areas to prevent visual interference.

6. Grading Environment

6.1 Light Source

We commonly use the D65 light source. The bulb lifespan is 2000 hours. Other light sources may be specified, such as F light source, 84-P light source, UV light source, etc.

6.2 Darkroom Lighting

Darkroom: The grading process must be conducted in a darkroom with constant humidity and temperature. Additionally, the walls and furnishings of the darkroom must be painted in a neutral gray shade, approximately matching the level between Grade 1 and Grade 2 on the gray scale (roughly equivalent to Munsell N5). As shown in the image above, the left side displays the neutral gray of the walls with the lights on, while the right side shows the color after the lights are turned off. The entire darkroom must be free of any light sources other than the light source from the grading lightbox. Furthermore, no other objects should be present on the grading table.

7. Observer's Line of Sight

Grading Angle

Grading samples using gray cards requires precise angles! This standard mandates:

- Sample positioned at 45° to the horizontal plane

- Grading light source at 45° to the sample

- Observer's eyes at 90° to the sample

Observer-to-sample distance: 50-70 cm.

8. Precautions for Viewing Color Fastness Evaluation Cabinets

8.1 Light Source is Critical: Grading must never be conducted under everyday indoor lighting (e.g., incandescent or fluorescent lamps), as results will be severely distorted.

8.2 Viewing Angle: During observation, the sample and gray card should be placed on the same plane, with the line of sight forming approximately a 45° angle to the sample surface.

8.3 Multiple-Rater Grading: For greater objectivity, two or more graders should independently evaluate samples, then average the ratings. If discrepancies exceed 0.5 grades, a third grader must re-evaluate or consensus must be reached through discussion.

Gray Scale Maintenance: Gray scales are precision instruments. Avoid soiling, scratching, and light exposure. Store in protective sleeves after use.

Gray scale grading represents the final presentation of colorfastness test results and constitutes the concluding step in colorfastness testing. Regardless of prior process accuracy and standardization, grading errors can invalidate the entire test. Grading remains a challenging task. Ensuring consistency among personnel within the same laboratory is crucial, as is maintaining consistency between testing institutions. As more brands collaborate with multiple laboratories, inter-laboratory consistency becomes increasingly vital.

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What is the toy safety test simulation little finger? At present, the safety of children's toy products has become the focus of attention in all countries, and safety is an important indicator for measuring toy products. How to find safety problems and solve them in time when designing and manufacturing toy products? How to avoid product recall due to non-compliance with the standards of toy importing countries? This requires testing of toy products.

Toy safety simulation of small fingers, in line with GB6675, EN71 and other standards of simulation testing, through the imitation of children's fingers, to assess whether touching the surface of the toy or accessories (points and surfaces of the toy) may lead to danger. There are two types of AB, A refers to be used for under 3 years old and B refers to be used for over 3 years old.

The test is performed by extending the articulating reachable probes towards the part or parts of the toy under test in any manner, with each probe rotated 90°to simulate finger joint movement. Finally, a part or component of a toy is considered to be accessible if any part before the shoulder of the shaft can reach it, visually identifying the potential hazards of the toy for everyone.

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Oil content is one of the key indicators for evaluating the performance of all fibers and fiber products except cotton, expressed as the percentage of oil content per unit mass. Different product standards use terms such as“residual fat content,”“oil content,” “dichloromethane-soluble substances,”or“ethanol extractables” as test item names.

1. In chemical fibers, oils primarily originate from additives introduced during spinning and textile processing. These additives prevent or eliminate static buildup while imparting softness and smoothness to the fibers. Oil content is a critical indicator for chemical fibers: excessively low levels may cause static electricity due to friction during production, while excessively high levels impair moisture absorption and increase susceptibility to dust accumulation.

2. The oils in feathers and down primarily originate from residual oils on duck and goose bodies after washing and disinfection processes. Excessive oil content can cause odors and bacterial growth, while insufficient oil affects the external structure of down, making it brittle and reducing the product's warmth.

3. The pupa oil in silk originates from silkworm cocoons. High oil content reduces elasticity, impairs moisture absorption and breathability, and causes odors.

4. As mammals, sheep possess sweat glands. Thus, physiological impurities in wool fibers primarily include sebaceous wax secreted by sebaceous glands, sweat secreted by sweat glands, and shed skin flakes. During raw wool processing, greasy wool sheared from sheep undergoes washing machines to remove sebaceous wax, sweat, and other impurities before drying to produce washed wool. Therefore, the oil content measured in the ethanol extract of washed wool is a key indicator of whether wool grease and sweat have been effectively removed, serving as a benchmark for evaluating washing quality.

5. During the process of combing washed wool into slivers, wool oil is added to impart smoothness, softness, and antistatic properties to loose fibers. This facilitates the passage of wool fibers through combing and spinning equipment, preventing issues like loose fibers, tangling, and breakage. Dichloromethane-soluble substances reflect components in cashmere knitwear extractable by dichloromethane solvent. These primarily include various lubricants added during production, such as spinning oils, detergents, and softeners, along with small amounts of residual natural wool grease wax. If the amount of wool oils added during production is improper, this indicator in the product may be elevated. In severe cases, this can lead to an unpleasant odor and a sticky feel.

6. Test Principle

Utilizing the property that fats and oils are soluble in organic solvents such as ether, dichloromethane, and ethanol, organic solvents are employed to extract fats and oils from the sample. The organic solvent is then evaporated in an oven. The residual fat and oil mass and the sample mass are weighed, and the oil content of the sample is calculated.

7. Test Standards

Standards vary depending on the product type, such as:

GB/T 14272—2011 “Down Garments” Appendix C: Determination of Residual Fat Content

FZ/T 20018—2010 “Determination of Dichloromethane-Soluble Substances in Wool Textiles”

GB/T 24252—2009 “Silk Quilts” Appendix C: Test Method for Oil Content in Fillings

GB/T 6504—2017 “Chemical Fibers—Test Method for Oil Content”

GB/T 6977—2008 Test Methods for Ethanol Extracts, Ash Content, Vegetable Impurities, and Total Alkali Insolubles in Cleaned Wool — Test Method for Ethanol Extracts in Cleaned Wool

8. Are different testing methods interchangeable?

Although oil content testing methods vary for different types of fiber products, the underlying principles remain consistent. These methods utilize solvents such as diethyl ether, dichloromethane, or ethanol to extract fats and oils from the sample. The solvent is then evaporated, leaving behind residual fat. The sample's oil content is calculated using a formula. The QuicExtra Rapid Fiber Oil Extractor is compatible with extraction solvents such as petroleum ether, diethyl ether, and dichloromethane.

9. Testing Equipment

QuicExtra Fiber Oil Rapid Extractor

Also known as the Fiber Oil Rapid Extractor, this device utilizes the principles of solvent penetration and evaporation (using solvents such as petroleum ether, diethyl ether, or other organic solvents) to dissolve oils within textile fibers. This enables the detection of oil content in wool and synthetic fiber samples. Featuring a 3-station design, it rapidly and thoroughly extracts oils within 10 minutes, automatically calculates oil content, and uploads results to the system upon confirmation.

The oil content of different textile fibers varies depending on fiber type and processing requirements. Below are typical oil content ranges for common textile fibers (for reference only), generally expressed as percentages:

Polyester: 0.3% - 1%

Nylon: 0.5% - 2%

Polypropylene: 0.2% - 0.8%

Acrylic: 1% - 3%

Wool: 1% - 3%

Cotton: Below 0.5%

Viscose: 0.3% - 0.8%

Modal: 0.2% - 0.5%

Aramid: 0.1% - 0.5%

Carbon Fiber: Below 0.05%

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In daily life, down penetration can occasionally occur in down jackets and duvets, creating a negative consumer experience.

1. Down Burst Factors

Down feathers in down products contain a large amount of stagnant air. When a down quilt is squeezed, the air inside the down product is expelled through the fabric and needle holes. These airborne particles, called down filaments (hereinafter referred to as flying filaments), are carried by the high-speed airflow and attached to the fabric of the quilt, causing down bursts.

Down bursts can occur for a variety of reasons, such as insufficient fabric density, large needle holes, or poor down quality. This directly impacts the appearance and warmth of the down.

1.1 Down Structure

Because down is composed of protein molecules with a unique tree-like structure, they are easily charged by friction, causing like charges to repel each other and leak through micropores or seams. When down is subjected to external forces, it tends to rebound. During this rebound, air bursts through the fabric, pushing down feathers out from both sides. Furthermore, down is composed of a large number of components, and the tips of down filaments, feathers, and feathers are sharp, making it easy for them to burst through the fabric.

1.2 High Unfinished Down Content

The higher the unfinished down content in a down, the more it will be pierced; conversely, the lower the unfinished down content, the less it will be pierced.

For example, in 90% down that meets the national standard GB/T 14272-2021 "Down Clothing," the detectable unfinished down content can reach up to 10%. With such a high unfinished down content, it's difficult to minimize or eliminate piercing.

Experimental data shows that as the total amount of unfinished down decreases, the number of pinhole-pierced down decreases. When the unfinished down content drops below 3%, the number of pinhole-pierced down decreases by over 80% compared to down with a 12% unfinished down content.

1.3 Low density of the outer and inner lining material, resulting in high air permeability

In existing down jacket construction, the outer fabric, lining, or lining material may all be used to encase the down, and come into close contact and friction with the down.

The lower the density of the outer and inner lining material, the larger the gaps between the fabric fibers, resulting in higher air permeability and an increased chance of flyaway fibers penetrating the fabric. Some companies use calendering or coating processes to reduce fabric air permeability, achieving better initial down-proofing properties. However, as the down jacket is washed and rubbed, the down-proofing effectiveness of calendering or coating diminishes, and down penetration increases. Only by increasing the fabric density to achieve an air permeability of 1-3 mm/s can long-lasting down-proofing properties be achieved.

1.4 Filling Sequence

Currently, most factories use down filling machines. There are two filling processes: filling first and then quilting the down bag; quilting the down bag first and then filling each cell with down. The first filling process is more efficient, as each quilting needle hole compresses some down. These down fibers are close to the needle holes and easily escape through them due to airflow or friction. The second filling process is less efficient, but the quilting needle holes don't compress the down. To escape, the fibers must penetrate the down surrounding them and escape with the airflow, making this process significantly more challenging than the first. Experimental data shows that the amount of down that escapes when quilting first and then filling is reduced by over 60% compared to filling first and then quilting.

Taking all of the above factors into consideration, if companies want to ensure low down penetration in down products, they must implement effective measures and increase product costs to address this issue.

2. Anti-Down Penetration Test Method (Rotating Box Method)

2.1 Ready-to-Draw Down Garments

Principle: The entire test sample is placed in a rotating box of a testing instrument containing shaped silicone rubber balls. The rotating box rotates at a constant speed, bringing the shaped silicone rubber balls to a certain height and impacting the sample within the box, simulating the various squeezing, rubbing, and collision experiences experienced by the test sample during wear. The overall anti-down penetration performance of the garment is evaluated by calculating the number of down, feathers, and down fibers that emerge from the sample per unit area.

2.2 Down Quilts

Principle: Sample bags of fixed size are cut from the down filling area/layer of a finished down quilt or composite down quilt and placed in a rotating box of the testing instrument filled with hard silicone balls. The rotating box rotates at a constant speed, carrying the silicone balls to a certain height, where they impact the sample inside the box, simulating the various squeezing, rubbing, and collision effects that down quilts experience during use. The overall down penetration resistance of the down quilt is evaluated by counting the number of feathers, down, and down fibers that emerge from the sample bag.

[GB/T 12705.2-2009 "Textiles - Test Method for Down Penetration Resistance of Fabrics - Part 2: Rotating Box Method"]

Evaluation of anti-down drilling performance:

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Regarding some questions about screw pumps, Anhui Shengshi Datang would like to share some insights with everyone.

  Causes and Hazards Analysis of Rod String Reverse Rotation in Screw Pump Wells

1. Analysis of Causes for Rod String Reverse Rotation in Screw Pump Wells

During oilfield extraction using Screw Pumps, reverse rotation of the rod string is a relatively common failure. The causes of this reverse rotation are complex, but the primary reason is the sudden shutdown or sticking of the pump during operation, which causes deformation and torsion of the rod string. The rapid release of this deformation and torsion then leads to reverse rotation. Specifically, if the Screw Pump suddenly stops or sticks during operation, a pressure difference arises between the high-pressure liquid retained in the production tubing and the wellbore hydrostatic pressure in the casing annulus. Driven by this pressure difference, the Screw Pump acts as a hydraulic motor, driving the rotor and the connected rod string to rotate rapidly in reverse.

The reverse rotation of the Screw Pump rod string is influenced by the tubing-casing pressure difference, exhibiting variations in reverse rotation duration and speed. Generally, a larger tubing-casing pressure difference results in faster reverse rotation speed and longer duration for the rod string. As the pressure difference gradually decreases, the reverse rotation speed and duration correspondingly decrease until the pressure difference balances, at which point the reverse rotation gradually ceases. When reverse rotation occurs, the rod string vibrates intensely. If resonance occurs during this vibration—meaning the vibration frequency of the reversing rod string synchronizes with the natural frequency of the wellhead—the rotation speed can instantly surge to its maximum. This situation can trigger serious safety accidents, cause significant harm to the worksite, and even result in casualties.

2. Hazards of Rod String Reverse Rotation in Screw Pump Wells

The hazards caused by rod string reverse rotation vary in degree depending on the speed and duration of the reversal. Severe cases can lead to onsite safety incidents with serious consequences. Specifically, the hazards mainly manifest in the following three aspects:

(1) Reverse rotation can cause the rod string to become displaced from its original position, leading to the swinging of the Screw Pump polish rod. This can cause significant wear and tear on the Screw Pump equipment, damaging various components and parts.

(2) During reverse rotation, if the speed is too high or the duration too long, the temperature of the reversing components can continuously rise, potentially igniting flammable gases at the wellhead. This could trigger an explosion at the worksite, leading to unforeseeable serious consequences.

(3) If reverse rotation is not effectively controlled, it can cause the drive pulley to shatter. Fragments of the pulley flying around the worksite pose a risk of injury to personnel, damage the oilfield production site, reduce extraction efficiency, and increase the probability of various safety incidents.

  Commonly Used Anti-Reverse Rotation Devices for Screw Pump Well Rod Strings

1. Ratchet and Pawl Type Anti-Reverse Device

This type of device prevents reverse rotation by utilizing the one-way engagement of a ratchet and pawl. Specifically, the ratchet and pawl engage via an external meshing configuration. When the Screw Pump drive operates normally, centrifugal force causes the pawl to disengage from the ratchet brake band, so the anti-reverse device remains inactive. However, when the Screw Pump suddenly stops during operation, the rod string begins to reverse due to inertia. During this reverse rotation, gravity and spring force cause the pawl to engage with the ratchet brake band, activating the anti-reverse device. The device then dissipates the torque generated by the high-speed reverse rotation through frictional force.

The ratchet and pawl device has a simple structure, is easy to install, has a low overall cost, and offers good flexibility and controllability. However, it typically requires manual intervention at close range for activation/operation. Improper operation can cause the friction surfaces to slip, presenting a safety risk. Additionally, this type of device can generate significant noise during operation and subjects the components to considerable impact and wear, necessitating frequent part replacements.

2. Friction Type Anti-Reverse Device

The friction type anti-reverse device consists of two main parts: an overrunning clutch that identifies rotation direction and a brake shoe assembly. In this device, the brake shoes are connected to the brake bodies via riveting, and the two brake bodies grip the outer ring. During normal Screw Pump operation (clockwise rotation), the device remains inactive. When a sudden shutdown causes reverse rotation, the drive mechanism reverses. In this state, rollers move between the star wheel and the outer ring, activating the device. The resulting damping effect restricts the rotation of the star wheel, thereby achieving the anti-reverse function. However, since the operation of this device often requires manual control, improper handling can lead to failure. Furthermore, replacing this device involves significant safety risks. Consequently, its application in Screw Pump wells is currently relatively limited.

3. Sprag Type Anti-Reverse Device

The sprag type anti-reverse device operates based on the principle of an overrunning clutch. Specifically, during normal Screw Pump operation (forward rod string rotation), the sprags inside the device align normally and remain disengaged from the outer ring, keeping the device inactive. When the pump suddenly stops and the rod string starts to reverse rotate, the resulting reverse torque causes the device to rotate in the opposite direction. This makes the sprags align in the reverse direction, locking them against the outer ring and preventing reverse rotation of the rod string.

The sprag type device has a simple construction, is easy to install, offers good controllability, and operates with high safety, minimizing the risk of accidents. It also has a long service life and does not require frequent part replacements. The drawback is that it cannot fundamentally solve the reverse rotation problem. If the reverse torque exceeds the capacity the sprags can withstand, it can cause sprag failure and device malfunction. Additionally, daily maintenance of this device can be inconvenient.

4. Hydraulic Type Anti-Reverse Device

The working principle of the hydraulic anti-reverse device is somewhat similar to a car's braking system. When the Screw Pump suddenly stops and the rod string is about to reverse rotate, the hydraulic motor within the device activates. Hydraulic fluid pressure drives friction pads against a brake disc, releasing a large amount of the reverse rotation potential energy, thereby dissipating the reverse rotation of the rod string.

The advantages of the hydraulic type device include stable and reliable operation, high safety, no noise generation, and no hazard to onsite personnel. Maintenance, replacement, and daily upkeep are relatively convenient and safe. This type of device can more thoroughly address the reverse rotation problem, enhancing the operational safety of the Screw Pump system. The disadvantages are its high overall cost and stringent quality requirements for the hydraulic components, leading to potentially higher maintenance and replacement costs. If issues like hydraulic fluid degradation or leaks occur during operation, the device's performance can be affected, necessitating regular maintenance.

  Measures to Address Rod String Reverse Rotation in Screw Pump Wells

1. Research and Application of Safer, More Reliable Anti-Reverse Devices

Analysis of the causes of rod string reverse rotation indicates that the main factors are the release of stored elastic potential energy in the rod string and the effect of the tubing-casing pressure difference. If reverse rotation is not effectively controlled, especially at high speeds or for prolonged durations, it can lead to a series of severe consequences and safety incidents, posing significant risks. Therefore, technical research and application should be strengthened. Based on existing anti-reverse devices, upgrades and improvements should be made to develop and apply safer and more reliable devices. These should ensure the safe release of torque and effective elimination of the pressure difference during sudden Screw Pump shutdowns, reducing associated safety risks. The working principles, advantages, and disadvantages of common anti-reverse devices need in-depth analysis for targeted improvements. This will enhance the stability and reliability of these devices, minimize safety risks during use, and maximize the operational safety of Screw Pump equipment.

2. Application of Downhole Anti-Backflow Switches

Using downhole anti-backflow switches can effectively address reverse rotation caused by hydraulic forces. The downhole anti-backflow switch consists of components like a disc, ball, push rod, shear pin, and crossover sub. Its application in the Screw Pump drive system can reduce the torque generated during sudden shutdowns, lower the reverse rotation speed, and mitigate reverse rotation caused by the tubing-casing pressure difference. By dissipating hydraulic forces, it helps control reverse rotation and also prevents rod string back-off. The anti-backflow switch has a simple structure, low cost, and is easy to install. It has been widely used in oilfield development due to its strong stability, high reliability, and broad application prospects.

3. Strengthening Surface Safety Management

To effectively control reverse rotation, it is essential not only to equip Screw Pump systems with appropriate anti-reverse devices but also to enhance safety management in surface operations and implement protective measures to reduce the adverse consequences of reverse rotation. Specific measures include:

① Personnel should perform daily inspection, maintenance, and servicing of Screw Pump equipment, maintain proper equipment management records, continuously accumulate experience, and improve safety prevention capabilities.

② Implement continuous monitoring of the Screw Pump system's operation to promptly detect abnormalities. Take immediate action for fault diagnosis and troubleshooting to reduce the probability of reverse rotation occurrences.

③ Establish comprehensive emergency response plans. For sudden reverse rotation events, immediately activate the emergency plan to lower the probability of safety incidents.

Working Principle of Centrifugal Pumps

The working principle of centrifugal pumps is based on the action of centrifugal force. When the impeller rotates at high speed, the liquid is thrown from the center of the impeller to the outer edge under the influence of centrifugal force, thereby gaining kinetic energy and pressure energy. The specific working process is as follows:

1.Liquid enters the central area of the impeller through the pump's suction inlet.

2.The rotation of the impeller generates centrifugal force, causing the liquid to move from the center of the impeller to the outer edge along the blade passages.

3.The liquid gains kinetic energy and pressure energy within the impeller and is then discharged into the pump casing.

4.Inside the pump casing, part of the liquid's kinetic energy is converted into pressure energy, and the liquid is ultimately discharged through the outlet.

During the operation of a centrifugal pump, the impeller does work by converting mechanical energy into the energy of the liquid. As the liquid flows through the impeller, both its pressure and velocity increase. According to Bernoulli's equation, the increase in the total energy of the liquid is primarily manifested as an increase in pressure energy, enabling the centrifugal pump to transport the liquid to a higher elevation or overcome greater system resistance.

It is important to note that the prerequisite for the normal operation of a centrifugal pump is that the pump cavity must be filled with liquid. This is because centrifugal force can only act on liquids and not on gases. If air is present in the pump cavity, the pump will be unable to build up pressure normally, resulting in "vapor lock," which ultimately leads to cavitation.

Analysis of Causes for Centrifugal Pump Cavitation

 1.Inadequate Inlet Medium or Insufficient Inlet Pressure

Inadequate inlet medium is one of the most common causes of centrifugal pump cavitation. The following situations may lead to insufficient inlet medium:

a. Low Liquid Level: When the liquid level in a pool, tank, or storage container falls below the pump's suction pipe or the minimum effective level, the pump may draw in air instead of liquid, resulting in cavitation.

b. Excessive Suction Lift: For non-self-priming centrifugal pumps, if the installation height exceeds the allowable suction lift, even if the suction pipe is immersed in the liquid, the pump will be unable to draw the liquid up, leading to a lack of liquid inside the pump. According to physical principles, the theoretical maximum suction lift for non-self-priming centrifugal pumps is approximately 10 meters of water column (atmospheric pressure value). However, considering various losses, the actual suction lift is typically below 6-7 meters.

c. Insufficient Inlet Pressure: In applications requiring positive inlet pressure, if the provided inlet pressure is lower than the required value, the pump may experience inadequate liquid supply, causing cavitation.

d. Poor System Design: In some system designs, if the suction pipeline is too long, the pipe diameter is too small, or there are too many bends, the pipeline resistance increases, reducing the inlet pressure and preventing the centrifugal pump from drawing liquid properly.

Case studies show that approximately 35% of centrifugal pump failures in the petrochemical industry are caused by inadequate inlet medium or insufficient inlet pressure. This issue is particularly common in oil transportation systems due to the high viscosity and vapor pressure of oil products.

 

 2.Blockage in the Inlet Pipeline

Blockage in the inlet pipeline is another common cause of centrifugal pump cavitation. Specific manifestations include:

a. Clogged Screens or Filters: During long-term operation, screens or filters in the inlet pipeline may become gradually blocked by impurities or sediments, restricting liquid flow.

b. Scale Formation Inside the Pipeline: Particularly when handling hard water, water with high calcium and magnesium ion content, or specific chemical liquids, scale or crystalline deposits may form on the inner walls of the pipeline, reducing the effective diameter over time.

c. Foreign Object Entry: Accidental entry of objects such as leaves, plastic bags, or aquatic plants into the suction pipeline can block elbows or valves, obstructing liquid flow.

d. Partially Closed Valves: Operational errors, such as failing to fully open valves in the suction pipeline, or internal valve malfunctions, can also lead to insufficient flow.

e. Foot Valve Failure: In systems equipped with foot valves, if the foot valve malfunctions (e.g., spring deformation or sealing surface damage), it can affect the pump's ability to draw liquid properly.

Statistical data indicate that approximately 25% of centrifugal pump cavitation cases in municipal water supply and drainage systems are caused by inlet pipeline blockages. This issue is especially common in wastewater treatment systems with high levels of suspended solids.

 

 

 3.Incomplete Air Removal from the Pump Cavity

Incomplete air removal from the pump cavity is a significant cause of centrifugal pump cavitation. Key manifestations include:

a. Inadequate Priming Before Initial Startup: After initial installation or prolonged shutdown, centrifugal pumps must be primed to remove air from the pump body. If priming is insufficient, residual air can prevent the pump from establishing normal working pressure.

b. Insufficient Self-Priming Capability: Non-self-priming centrifugal pumps cannot expel air on their own and rely on external priming. While some self-priming pumps have a certain self-priming capability, improper startup methods or excessive self-priming height can lead to poor air expulsion.

c. Air Leaks in the Pipeline System: Minor cracks in suction pipeline connections, sealing points, or aging pipes can allow air to enter the system under negative pressure. This is particularly hazardous because even if the pump is initially primed correctly, air can accumulate over time, eventually causing cavitation.

d. Seal Failure: Worn or improperly installed shaft seals (e.g., mechanical seals or packing seals) can allow external air to enter the pump, especially when the suction side pressure is below atmospheric pressure.

In industrial applications, approximately 20% of centrifugal pump cavitation cases are caused by incomplete air removal from the pump cavity. This issue is particularly common during initial startup after installation or maintenance.

 

 4.Other Causes

In addition to the main causes mentioned above, other factors can also lead to centrifugal pump cavitation:

a. Liquid Vaporization: When handling high-temperature or highly volatile liquids, if the suction pipeline pressure falls below the liquid’s saturation vapor pressure at that temperature, the liquid may vaporize, forming bubbles. This can prevent the pump from drawing liquid or cause cavitation.

b. Operational Errors: Human factors, such as incorrect valve operation or failure to follow startup procedures, can lead to pump cavitation.

c. Control System Malfunctions: In automated control systems, failures in level sensors, pressure sensors, or errors in PLC programming logic may cause the pump to start or operate under inappropriate conditions, resulting in cavitation.

d. Power or Motor Issues: Incorrect power phase sequence causing motor reversal can prevent the pump from drawing liquid properly. Voltage instability causing motor speed fluctuations can also disrupt normal pump operation.

e. Temperature Effects: In extreme environmental conditions, such as cold regions, inadequate insulation may cause liquid in the pipeline to freeze, obstructing flow. In high-temperature environments, liquids may vaporize, forming vapor locks.

Research indicates that these other causes account for approximately 20% of centrifugal pump cavitation cases. Although the proportion is relatively small, they can be significant factors in specific scenarios or conditions and should not be overlooked.

Seal-free self-priming pumps are primarily used for low-level lifting in the wastewater treatment system of the Second Purification Plant, replacing submersible sewage pumps and long-shaft submerged lift pumps in suction tanks. In summary, the use of seal-free self-priming pumps offers simple operation and reduced maintenance workload, making them highly suitable for the wastewater treatment system in natural gas purification plants where safety requirements are critical. Anhui Shengshi Datang now provides an analysis and summary of the usage of seal-free self-priming pumps.

1. Structure and Working Principle of Seal-Free Self-Priming Pumps

(1) Basic Structure of Self-Priming Pumps

Typically, the basic structure of a self-priming pump mainly includes the following components: a liquid storage chamber, a pump body rotor, inlet and outlet valves, a motor, and several other parts that together form the pump.

(2) Basic Working Principle of Seal-Free Self-Priming Pumps

The working principle primarily involves the following processes: first, self-priming and exhaust; second, normal pumping of liquid.

2. Analysis of the Practical Usage of Seal-Free Self-Priming Pumps

(1) Advantages of Seal-Free Self-Priming Pumps in Low-Level Liquid Transport

① Small seal-free self-priming pumps do not require specialized installation foundations or anchor bolts. They can be placed horizontally, making installation simple. They can easily replace existing lift pumps or submersible pumps.

② Easy operation. Normal operation only requires priming the pump once, after which starting and stopping can be done effortlessly.

③ Strong self-priming capability. Within the suction range, they can replace submersible electric pumps, reducing safety hazards.

④ No sealing required. Completely eliminates leakage, dripping, and seepage. During operation, the sealing device does not experience friction, extending its lifespan by more than 10 times. The self-priming performance is stable and reliable, requiring only one initial priming for lifelong self-priming, with superior self-control capability.

⑤ No need for a separate suction device, resulting in a simpler structure and safer operation.

⑥ Maintenance of seal-free self-priming pumps is convenient. These devices rarely malfunction, are easier to maintain compared to other equipment, and do not require significant financial investment.

 

(2) Specific Analysis of the Technical Performance of Seal-Free Self-Priming Pumps

① Due to the simple structure of self-priming pumps and the use of dynamic combined airflow sealing, the pump's operation does not affect the sealing device. Compared to long bearings, this device is easier to operate and has a lower probability of issues.

② The device primarily relies on the principle of air-water separation, giving it strong self-priming performance. Especially after using an "air control valve," the siphon phenomenon can be maximally disrupted, achieving the effect of lifelong self-priming.

③ The drawback is that it does not have a high work efficiency and consumes more energy.

④ After starting the self-priming pump, it takes some time before water is discharged. Therefore, designers of pump stations must pay attention to this situation, meaning multiple backup pumps should be prepared.

⑤ When a self-priming pump is used to lift wastewater, certain parameters such as flow rate, head, and suction head must be kept within allowable limits. Otherwise, equipment malfunctions may occur, adversely affecting the pump's smooth operation.

⑥ Based on the basic principle of self-priming pumps, it is essential to ensure that the connections at the water pipe interfaces are properly sealed. If the pump experiences insufficient flow, it may fail to operate smoothly.

3. Technological Innovations

(1) Installation of an Air Valve in the Suction Pipeline to Disrupt the Siphon Phenomenon and Retain Sufficient "Priming Liquid" in the Pump Cavity

① In the early stages of using seal-free self-priming pumps, the electric air valves designed by manufacturers were not installed, mainly because they were unsuitable for flammable and explosive environments. Additionally, air valves of this model had many defects, such as frequent malfunctions. Therefore, personnel should use solenoid valves as air valves based on actual application conditions, significantly improving durability and stability.

② Function and Principle of the Electric Air Control Valve

The air valve is typically installed at the high point of the self-priming pump's suction pipe. When the pump starts, the solenoid valve is energized, and the valve core seats downward, ensuring the suction pipeline is sealed to achieve self-priming. When the pump stops, the air valve opens, allowing air to enter the pipe cavity. This separates the liquid in the suction pipe and pump cavity, preventing backflow of the liquid in the pump cavity. This completely disrupts the siphon phenomenon, ensuring the self-priming pump operates normally during the next self-priming cycle. The air valve is particularly suitable for self-priming pumps that start and stop frequently, reducing the need for priming operations.

(2) Use of Steel Wire Flexible Hoses in the Suction Pipe to Facilitate Daily Maintenance and Troubleshooting of Self-Priming Pumps

① Typically, self-priming pumps in wastewater systems, like other pumps, require regular cleaning at specific intervals. If the suction tank is deep, maintaining metal suction pipes requires collaboration among several personnel.

② If the suction pipe of the self-priming pump operates under negative pressure, such as when pinholes occur, insufficient air may reach the pump, preventing normal operation. Moreover, such issues are not easily detectable. By using steel wire flexible hoses, if leakage points occur, the hose can be pulled back to the ground for inspection promptly.

(3) Adjusting the Pump Outlet Diameter to Prevent Motor Overload

① From the perspective of seal-free self-priming pumps, some manufacturers fail to achieve precision during production, resulting in inconsistent power output between the motor and the pump body. This can easily lead to overload situations.

② During specific applications, personnel need to adjust the flow path based on the actual degree of overload to ensure the pump's flow rate remains within allowable limits.

 

Centrifugal pumps are widely used in industrial production and engineering systems for conveying various liquid media. However, during operation, a phenomenon that severely affects pump performance and service life often occurs—cavitation. Cavitation not only reduces the efficiency of centrifugal pumps but also causes serious damage to key components such as impellers, and can even lead to the complete scrapping of the equipment. Therefore, studying and understanding the causes of cavitation in centrifugal pumps is of great significance for the rational design, correct installation, and safe operation of pumps. Below, Anhui Shengshi Datang will provide you with a detailed introduction.

1. Basic Concept of Cavitation

Cavitation refers to the phenomenon where, as liquid flows through the pump impeller, the local pressure drops below the saturated vapor pressure of the liquid at its operating temperature, causing partial vaporization of the liquid and the formation of numerous tiny vapor bubbles. When these bubbles are carried by the liquid flow into a region of higher pressure, the surrounding pressure rapidly increases, causing the bubbles to collapse instantaneously and condense back into liquid. The collapse of these bubbles generates intense shock waves and localized high temperatures, which impact the impeller surface, leading to fatigue pitting or spalling of the metal. This is the cavitation phenomenon in centrifugal pumps.

The essence of cavitation is the result of the combined action of fluid dynamics and thermodynamics. The fundamental cause is the uneven pressure distribution within the liquid. When the local flow velocity is too high or the geometric design is unreasonable, the local pressure drops, triggering the cyclic process of vaporization and bubble collapse.

2. Root Cause of Cavitation

The root cause of cavitation in centrifugal pumps is that the local pressure of the liquid within the pump falls below the saturated vapor pressure of the liquid at that temperature. In a centrifugal pump, liquid flows from the suction pipe into the impeller inlet. As the flow passage gradually contracts, the liquid velocity increases, and the static pressure consequently decreases. When the local pressure drops to the saturated vapor pressure of the liquid, the liquid begins to vaporize, generating vapor bubbles. These bubbles are carried into the high-pressure region towards the middle and outlet of the impeller, where they rapidly collapse under the high pressure. The high-energy shock waves released during bubble collapse cause metal erosion on the impeller surface, increased pump vibration, enhanced noise, and problems such as reduced flow rate and head.

3. Main Factors Leading to Cavitation

a. Excessive Suction Lift: If the pump is installed too high or the suction liquid level is too low, the pressure on the suction side decreases. As the liquid flows towards the impeller inlet, the pressure drops further. When it falls below the saturated vapor pressure, vaporization occurs. If the suction lift exceeds the allowable NPSH (Net Positive Suction Head), cavitation is inevitable.

b. Excessive Suction Line Resistance: A suction pipeline that is too long, too narrow, has too many elbows, or has a partially closed valve causes significant frictional and local pressure losses. The reduced pressure at the suction end leads to a further pressure drop at the impeller inlet, making cavitation more likely. Additionally, air leakage or poor sealing in the suction piping can introduce gas into the liquid, exacerbating cavitation.

c. Excessively High Liquid Temperature: An increase in liquid temperature significantly raises its saturated vapor pressure, making the liquid more prone to vaporization. For example, the saturated vapor pressure of water is relatively low at room temperature but increases substantially at high temperatures. Even if the suction pressure remains unchanged, the vaporization condition might be met when the temperature rises, thus triggering cavitation.

d. Low Inlet Pressure or Reduced Ambient Pressure: When the pressure at the pump suction source decreases—such as due to a drop in liquid level, a vacuum in the supply container, or low ambient atmospheric pressure (e.g., at high altitudes)—the pressure at the suction port becomes insufficient, making it very easy for the liquid to vaporize at the impeller inlet.

e. Improper Pump Design or Installation: The structural design of the pump directly affects its cavitation performance. For instance, an impeller inlet diameter that is too small, an unreasonable blade leading edge angle, or a rough impeller surface can cause unstable liquid flow, leading to a sharp local pressure drop. Furthermore, failure to follow the manufacturer's provided Required NPSH (NPSHr) requirements during installation, or installing the pump at an excessive height, can also lead to cavitation.

f. Improper Operating Conditions: When the pump operates at flow rates deviating from the design point, runs for extended periods at low flow, or during sudden valve adjustments, the pressure distribution of the fluid changes, which can also cause local vaporization and cavitation.

4. Effects and Hazards of Cavitation

The hazards of cavitation to centrifugal pumps are mainly manifested in the following aspects:

a. Metal Surface Damage: The high-pressure shocks generated by collapsing bubbles cause pitting erosion on the impeller surface. Long-term development can lead to material fatigue, spalling, and even perforation of the impeller.

b. Performance Degradation: Cavitation leads to a significant reduction in flow rate, head, and efficiency, altering the pump's characteristic curves.

c. Vibration and Noise: The impact forces generated by cavitation cause mechanical vibration and high-frequency noise, affecting the stable operation of the equipment.

d. Reduced Service Life: Long-term operation under cavitation conditions accelerates mechanical wear, shortening the service life of bearings, seals, and the impeller.

5. Measures to Prevent Cavitation

To prevent or mitigate cavitation, measures should be taken from the perspectives of design, installation, and operation:

a. Select a reasonable installation height to ensure sufficient pressure on the suction side, making the Available NPSH (NPSHa) greater than the pump's Required NPSH (NPSHr).

b. Optimize the suction pipeline by shortening its length, reducing the number of elbows, increasing the pipe diameter, keeping suction valves fully open, and avoiding air ingress.

c. Control the liquid temperature through cooling or lowering the storage tank temperature to reduce the liquid's saturated vapor pressure.

d. Increase the inlet pressure, for example, by installing a booster pump, pressurizing the liquid surface, or placing the liquid container at a higher elevation.

e. Improve the impeller structure by using materials and geometries with good anti-cavitation properties, such as adding an inducer or optimizing the blade inlet angle.

f. Keep the pump operating near its design point, avoiding prolonged operation at low flow rates or other abnormal operating conditions.

In summary, the occurrence of cavitation in centrifugal pumps is primarily caused by the pressure of the liquid at the impeller inlet being too low, falling below its saturated vapor pressure, which triggers vaporization and subsequent bubble collapse. Specific factors leading to this phenomenon include excessive suction lift, excessive suction resistance, high liquid temperature, low inlet pressure, and improper design or operation. Cavitation not only affects pump performance but also causes severe damage to the equipment. Therefore, in both design and operation, emphasis must be placed on the prevention and control of cavitation. By rationally configuring the system, optimizing structural parameters, and improving operating conditions, the safe and efficient operation of centrifugal pumps can be ensured.

 

 

In the structure of a centrifugal pump, the mechanical seal is a core component, directly related to the stable operation and service life of the equipment. The primary function of the mechanical seal is to prevent fluid leakage from the pump, ensuring its normal operation and working efficiency. However, in practical applications, the mechanical seal of centrifugal pumps is often affected by factors such as operating conditions, medium characteristics, and operational maintenance, leading to failures. This results in seal damage, pump leakage, and even equipment shutdown, adversely impacting production safety and environmental protection. Failure of the centrifugal pump mechanical seal not only affects the equipment's performance and safety but also leads to high maintenance costs, increasing production expenses for oilfield enterprises. Therefore, researching the causes and damage mechanisms of mechanical seal failures in centrifugal pumps, and subsequently proposing effective prevention and improvement measures, is of significant importance for reducing the failure rate of mechanical seals and extending their service life. Anhui Shengshi Datang will give you an overview.

1. Analysis of Centrifugal Pump Operating Principle

The operation of a centrifugal pump is based on Bernoulli's equation in fluid dynamics, which states that within a closed system, the energy of a fluid comprises kinetic energy, potential energy, and pressure energy, and these three forms of energy are converted within the pump. The core components of a centrifugal pump are the impeller and the pump casing. When the electric motor drives the pump shaft to rotate, the impeller rotates at high speed, causing the liquid inside the pump to also undergo rotational motion. Under the action of centrifugal force, the liquid is thrown from the center of the impeller towards its periphery, gaining an increase in both kinetic and pressure energy. This change in kinetic and pressure energy causes the liquid to flow out through the pump casing outlet. The pressure at the center of the impeller decreases, forming a low-pressure area, and liquid is continuously drawn into the pump under atmospheric pressure, thus forming a continuous liquid transport process. The operation of a centrifugal pump can be divided into three stages: liquid suction, acceleration, and discharge. In the suction stage, due to the low-pressure zone formed at the impeller center, external liquid flows into the pump under atmospheric pressure. In the acceleration stage, the liquid, acted upon by centrifugal force through the impeller, accelerates towards the pump casing. In the discharge stage, the high-speed liquid is gradually decelerated through the diffuser or volute, converting kinetic energy into pressure energy before being discharged from the pump.

The main components of a centrifugal pump include the impeller, pump casing, pump shaft, mechanical seal, and bearings. The impeller, made of materials like cast iron, stainless steel, or plastic, is the core component. Its design directly determines the pump's flow rate and head. Parameters such as the impeller's shape, size, number of blades, and blade angle significantly affect liquid flow and pressure conversion efficiency. The pump casing, typically volute-shaped, contains the fluid. Its main functions are to collect liquid discharged from the impeller and guide it to the discharge outlet. The casing also facilitates energy conversion by gradually converting the liquid's kinetic energy into pressure energy through diffusion, thereby increasing the pump's head. The pump shaft, driven by the motor and connected to the impeller, transmits mechanical energy from the motor to the impeller, causing it to rotate. The pump shaft must possess high strength and stiffness to withstand centrifugal forces and the reaction forces of the liquid on the impeller. The mechanical seal prevents liquid leakage at the point where the pump shaft and casing interact. Its performance directly affects the pump's efficiency and safety. Bearings support and fix the pump shaft, reducing friction and vibration during rotation, ensuring stable pump operation.

2. Causes of Leakage in Centrifugal Pump Mechanical Seals

(1) Trial Run Leakage.​ The installation precision of the mechanical seal directly affects its sealing effectiveness. If the seal faces are not accurately aligned during installation or if the face gap is set improperly, leakage can occur during trial operation. The stationary and rotating rings should be flat and aligned during installation. Failure to meet this standard can result in poor contact between the sealing faces, creating gaps and allowing medium leakage. Similarly, improper tightening according to design requirements or vibration during installation can cause misalignment of the seal rings, compromising the seal. During the trial run phase, the seal faces may not be fully bedded-in. Under high-speed operation and friction, face wear can lead to leakage. This wear is common if the seal faces have not been pre-treated or run-in, as initial high surface roughness increases frictional heat, exacerbating wear. Face wear reduces the contact integrity of the sealing surfaces, leading to leakage. Additionally, excessively rapid temperature rise during trial runs can cause uneven thermal expansion of the faces, accelerating wear. Vibration generated during pump operation due to bearing wear, imbalance, or other mechanical issues can affect the mechanical seal, which is sensitive to vibration. Vibration causes uneven pressure distribution between the seal faces, potentially leading to misalignment of the rotating and stationary rings, seal failure, and leakage. Particularly during trial runs, excessive axial shaft movement or radial runout beyond standards can adversely affect the stability of the seal components.

(2) Static Test Leakage.​ In mechanical seals, auxiliary sealing elements are typically made of materials like rubber or PTFE. The elasticity and corrosion resistance of these materials significantly impact sealing performance. Improper material selection for auxiliary seals can lead to leakage during static pressure testing. If the seal material lacks corrosion resistance or temperature tolerance, it may deform under static test pressure or temperature, failing to provide an effective seal. Simultaneously, aging, hardening, or loss of elasticity due to temperature changes can prevent the seal faces from fitting tightly, causing leakage. During static testing, pressure within the seal chamber should not fluctuate significantly. Otherwise, uneven pressure on the seal faces may cause leakage. Static tests are usually conducted at slightly higher pressures than operating pressure to verify seal integrity. However, if the pressure is too high or applied unevenly, the seal components can be damaged, compromising the contact between the stationary and rotating rings and causing leakage. Especially during static tests, if the liquid temperature is high, thermal expansion within the seal chamber can cause pressure fluctuations, leading to inadequate sealing. The seal faces, often made of wear-resistant, high-strength materials like silicon carbide or ceramic, are critical. If subjected to excessive pressure during installation or static testing, minor deformation can occur, affecting the faces' ability to mate properly.

(3) Operational Leakage.​ The operating conditions of a centrifugal pump may change with its working state. Variations in fluid temperature, pressure, or flow rate can all affect seal performance. When operating conditions exceed the seal's design limits—such as excessively high temperature or pressure—the material properties of the seal components can degrade, leading to seal failure. Leakage is particularly likely during transient flow fluctuations or under highly variable load conditions. Mechanical seals often rely on the presence of a seal fluid for adequate lubrication and cooling. Insufficient seal fluid flow or excessively high temperature can cause the seal fluid to evaporate or vaporize, reducing sealing effectiveness. Furthermore, impurities or contaminants in the seal fluid can enter the seal chamber, impairing lubrication between the seal faces, accelerating wear, and causing leakage. The material selection and design of the mechanical seal are directly related to its performance. If the seal material has insufficient corrosion resistance, it may corrode when exposed to the pump fluid, leading to decreased sealing performance. Similarly, poor design can cause uneven force distribution on the seal faces or issues related to thermal expansion, resulting in seal failure. Therefore, appropriate material selection and sound design are crucial factors for ensuring the stability of the mechanical seal during normal operation.

(4) Cooling Water Quality.​ The role of cooling water is to ensure temperature control for the mechanical seal, preventing seal failure due to high temperatures. If the cooling water quality does not meet standards, it can lead to mechanical seal leakage. If the cooling water contains impurities, solid particles, oil contamination, or other pollutants, it can negatively impact the working environment of the mechanical seal. These impurities may enter the seal chamber, causing wear on the stationary and rotating rings, reducing the smoothness of the seal faces, and thus inducing leakage. Simultaneously, the presence of pollutants can obstruct the flow of cooling water, preventing it from effectively carrying away the heat generated at the seal faces, further exacerbating wear and temperature rise. The chemical composition of the cooling water can also affect the materials of the mechanical seal. Cooling water containing high concentrations of corrosive agents can accelerate the corrosion of seal materials, reducing their service life. If the materials used in the mechanical seal are not corrosion-resistant, prolonged exposure to such cooling water can lead to cracks, pitting, or spalling on the seal faces, ultimately causing leakage. The temperature of the cooling water is crucial for the performance of the mechanical seal. If the cooling water temperature is too high, it may cause softening or aging of the seal materials, reducing their elasticity and sealing effectiveness. As temperature increases, the seal components may not maintain the designed tight contact, leading to leakage.

Anhui Shengshi Datang Pump Industry is committed to providing customers with the best technology and services, always putting customers at the core.

  Introduction to Pneumatic Diaphragm Pumps

A pneumatic diaphragm pump uses compressed air as its driving power source. It typically consists of components such as an air inlet, air distribution valve, balls, ball seats, diaphragms, connecting rods, central bracket, pump inlet, and exhaust outlet. Once it receives a control command, the pump starts operating by utilizing air pressure and its special internal structure to transfer materials. It has low requirements for the properties of the conveyed medium and can handle a wide range of substances, including solid–liquid mixtures, corrosive acid and alkali liquids, volatile, flammable, and toxic fluids, as well as viscous materials. It offers high working efficiency and simple operation. However, due to aging parts or improper use, diaphragm pump failures may occur during operation.

A. Materials

Pneumatic diaphragm pumps are commonly made from four materials: aluminum alloy, engineering plastics, cast alloy, and stainless steel. Depending on the medium being handled, the pump materials can be adjusted accordingly to meet the diverse needs of users. Owing to its adaptability to different environments, the pump can handle materials that conventional pumps cannot, earning it wide recognition among users.

B. Working Principle

The diaphragm pump operates by using a power source to drive the piston, which in turn moves hydraulic oil back and forth to push the diaphragm, thereby achieving suction and discharge of liquids. When the piston moves backward, the change in air pressure causes the diaphragm to deform and concave outward, increasing the chamber volume and decreasing pressure. When the chamber pressure drops below the inlet pressure, the inlet valve opens, allowing fluid to flow into the diaphragm chamber. Once the piston reaches its limit, the chamber volume is at its maximum and the pressure is at its minimum. After the inlet valve closes, the suction process is complete, and liquid filling is achieved.

As the piston moves forward, the diaphragm gradually bulges outward, decreasing the chamber volume and increasing internal pressure. When the pressure in the chamber exceeds the resistance of the outlet valve, the liquid is expelled. Once the piston reaches the external limit, the outlet valve closes under gravity and spring force, completing the discharge process. The diaphragm pump then proceeds to the next suction and discharge cycle. Through continuous reciprocation, the diaphragm pump effectively transfers the liquid.

C. Characteristics

1. Low heat generation: Powered by compressed air, the exhaust process involves air expansion, which absorbs heat, reducing the operating temperature. Since no harmful gases are emitted, the air properties remain unchanged.

2. No spark generation: As it does not rely on electricity, static charges are safely discharged to the ground, preventing spark formation.

3. Can handle solid particles: Due to its positive displacement working principle, there is no backflow or clogging.

4. No impact on material properties: The pump merely transfers fluids and does not alter their structure, making it suitable for handling chemically unstable substances.

5. Controllable flow rate: By adding a throttling valve at the outlet, the flow rate can be easily adjusted.

6. Self-priming capability.

7. Safe dry running: The pump can operate without load without damage.

8. Submersible operation: It can work underwater if needed.

9. Wide range of transferable liquids: From water-like fluids to highly viscous substances.

10. Simple system and easy operation: No cables or fuses are required.

11. Compact and portable: Lightweight and easy to move.

12. Maintenance-free operation: No lubrication needed, eliminating leakage and environmental pollution.

13. Stable performance: Efficiency does not decline due to wear.

  Common Failures and Causes

Although pneumatic diaphragm pumps are compact and occupy little space, their internal structure is complex, with many interconnected components. Failure of any single part can lead to operational problems. Unusual noise, fluid leakage, or control valve malfunctions are typical warning signs. Timely maintenance is essential. Component wear and aging caused by friction are also major sources of malfunction.

A. Pump Not Operating

1. Symptoms: When starting, the pump either does not respond or stops running shortly after starting.

2. Causes:

a. Circuit issues such as disconnection or short circuit prevent proper operation.

b. Severe component damage — for example, worn ball valves or damaged air valves — leads to loss of pressure and system shutdown.

B. Blocked Inlet or Outlet Pipeline

1. Symptoms: Reduced working pressure, weak suction, and slow fluid transfer.

2. Causes:

a. High-viscosity materials adhere to the inner pipe walls, reducing diameter and smoothness, increasing resistance.

b. Use of multiple materials without thorough cleaning causes chemical reactions between residues, affecting normal operation.

C. Severe Ball Seat Wear

Continuous friction wears down the surface of the ball seat, creating gaps between the ball and seat. This may cause air leakage and reduced pump output.

D. Severe Ball Valve Wear

1. Symptoms: Irregular ball shape, visible surface pitting, or heavy corrosion reducing ball diameter.

2. Causes:

a. Manufacturing inconsistencies cause mismatch between the ball and seat.

b. Long-term operation under friction and corrosive environments accelerates valve damage.

E. Irregular Pump Operation

1. Symptoms: The pump fails to complete normal suction and discharge cycles even after adjustment.

2. Causes:

a. Worn or damaged ball valve.

b. Aged or broken diaphragm.

c. Incorrect system settings.

F. Insufficient Air Supply Pressure or Poor Air Quality

Insufficient air pressure leads to reduced gas volume entering the air chamber, resulting in inadequate force to drive the connecting rod reciprocation. Increasing air pressure typically resolves this issue. Additionally, poor air quality can hinder the movement of the linkage rod and reduce motor speed, weakening pump output.