1. Classification and Characteristics of Chemical Conveying Media
1.1 Strong Corrosive Acidic Media
Including concentrated sulfuric acid, hydrochloric acid, nitric acid, mixed acid, etching solution and pickling waste liquid. Such media have strong oxidation and penetration corrosion, which can rapidly damage ordinary metal and plastic materials. They require high-grade anti-corrosion lining and all-PTFE wetted structure.
1.2 Alkaline Chemical Media
Caustic soda, potassium hydroxide, alkaline cleaning liquid and saponification liquid. Alkali liquid is easy to crystallize at low temperature and causes embrittlement and aging of partial rubber materials.
1.3 Organic Solvent Media
Ethanol, acetone, ethyl acetate, toluene, xylene and chemical diluents. Organic solvents have strong solubility, which easily causes swelling, softening and permanent deformation of ordinary rubber seals.
1.4 Crystallizable Salt Media
Sulfate, phosphate, chloride salt solution and electroplating bath liquid. Salt chemical liquid precipitates crystals after cooling, which is the main cause of valve ball jamming and pipeline blockage in chemical workshops.
1.5 High-Viscosity Chemical Fluids
Chemical resin, glue, paint, latex and high-concentration slurry. High-viscosity media increase fluid resistance and require large-flow wide-channel pump structure.
1.6 Solid-Liquid Mixed Slurry
Catalyst powder, chemical sediment, slag waste liquid and industrial sludge. Hard particles produce continuous scouring and piercing wear on diaphragms and valve seats.
2. Structural Composition and Working Principle
2.1 Three Core Structural Modules
2.1.1 Pneumatic Power Assembly
Composed of air distribution valve, sliding spool, air chamber, silencer and air inlet connector. Driven by compressed air, this part provides reciprocating power for the pump. Since it does not contact chemical liquid, the main failures are moisture rusting and low-temperature icing caused by humid workshop environment.
2.1.2 Chemical Wetted Assembly
Including pump cavity, one-way valve ball, valve seat, diaphragm and sealing gaskets. All wetted parts directly contact hazardous chemicals, which determine the corrosion resistance and service life of the whole pump. It is the core vulnerable area of chemical diaphragm pumps.
2.1.3 Connecting and Fixing Assembly
Including central drive shaft, flange connector, clamp and damping base. Long-term chemical vibration easily causes bolt loosening and medium leakage.
2.2 Basic Working Principle
Compressed air pushes the double-sided diaphragms to perform alternating reciprocating movement. The volume change inside the cavity forms negative pressure to suck chemical medium and positive pressure to complete liquid discharge. The one-way valve group controls unidirectional flow to avoid medium backflow. Without mechanical shaft contacting liquid and dynamic sealing structure, the pump realizes zero leakage delivery of toxic and corrosive chemicals. It supports explosion-proof operation, dry running and adjustable flow, fully adapting to complex chemical reaction processes.
3. Material Classification and Chemical Selection Criteria
3.1 Pump Housing Material Selection
3.1.1 PP/PVDF Plastic Housing
Applicable for weak acid, waste water and low-corrosion salt solution. Low cost and light weight; not resistant to high temperature and strong organic solvents.
3.1.2 304/316L Stainless Steel Housing
Suitable for fine chemical industry, alcohol solvent, neutral liquid and medical raw liquid. Smooth inner wall meets sanitary standards; strictly prohibited for chloride-containing brine and strong acid.
3.1.3 PTFE/FEP Teflon Lined Housing
Used for concentrated strong acid, mixed acid and strong oxidizing liquid. It has the highest chemical inertness and can resist almost all corrosive chemicals; limited by soft texture and temperature resistance.
3.2 Diaphragm and Seal Material Matching
Sealing Material
Applicable Chemical Medium
Inapplicable Medium
EPDM
Weak acid, inorganic salt, water-based liquid
Organic solvent, strong alkali
NBR
Oil chemical, hydrocarbon solvent
Strong acid, ketone liquid
FKM/Viton
Ketone, ester, benzene organic solvent
High-temperature strong alkali
PTFE
Strong acid, strong alkali, all corrosive liquid
Molten alkali metal
4. Unique Advantages and Working Condition Limitations in Chemical Industry
4.1 Core Application Advantages
Zero leakage safety performance: No mechanical dynamic seal to prevent toxic and harmful chemical liquid leakage and chemical gas diffusion.
Intrinsic explosion-proof: Air-driven structure without electric spark, suitable for flammable and explosive solvents such as ethanol and toluene.
Dry running permission: No burning risk under idle running, adapting to intermittent feeding of chemical reaction kettles.
Strong self-priming capacity: No need for liquid filling, suitable for underground chemical storage tank liquid extraction.
Wide viscosity adaptability: Normally convey thin solvent and high-viscosity resin slurry.
Adjustable flow and pressure: Stepless air pressure adjustment to meet chemical titration, circulation and transfer requirements.
4.2 Inherent Chemical Working Condition Defects
Chemical corrosion causes material aging and component damage;
Salt solution crystallization blocks valve passages;
Organic solvent dissolves and swells rubber accessories;
Volatile chemical liquid generates vapor to form air blockage;
Hard particles continuously scour and pierce diaphragms.
5. Eight Typical Chemical Exclusive Faults and Troubleshooting
Fault 1: Intermittent operation and jamming shutdown
Main Causes
High humidity in chemical workshop leads to water accumulation in air source; volatile chemical gas enters pneumatic cavity; salt crystals adhere to valve balls to block reset movement.
Solutions
Install air dryer and oil-water separator; regularly clean silencer and air passage; disassemble liquid end to remove crystalline deposits.
Fault 2: Difficult liquid suction and air blockage of volatile solvent
Main Causes
Low-boiling organic solvents vaporize easily, forming air bags inside the pump cavity to destroy negative pressure; air leakage of chemical corrosion pipeline joints aggravates air blockage.
Solutions
Install exhaust valve and anti-vacuum pipeline; replace corrosion-resistant sealed hoses; reduce suction height and shorten inhalation pipeline.
Fault 3: Rubber diaphragm swelling and deformation by organic solvent
Main Causes
Improper selection of ordinary rubber materials; ketone, ester and benzene solvents erode rubber molecular structure to cause permanent swelling.
Solutions
Replace with FKM fluororubber or PTFE composite diaphragm; prohibit universal use of ordinary rubber in solvent working conditions.
Fault 4: Crystallization locking and failure to restart after shutdown
Main Causes
Inorganic salt chemical liquid precipitates crystals after cooling; residual medium solidifies between valve ball and valve seat without flushing.
Solutions
Flush pump cavity with clean water or neutralizing liquid immediately after shutdown; install heat preservation pipeline for salt solution; disassemble and clean valve group regularly.
Fault 5: Pump body corrosion, perforation and material peeling
Main Causes
Serious wrong material selection: stainless steel conveys chloride salt; plastic pump contacts strong acid; lining delamination caused by temperature difference expansion.
Solutions
Reclassify chemical medium and replace matched pump type; polish and passivate corroded stainless steel surface; directly eliminate severely delaminated lining pump.
Fault 6: Diaphragm damage and liquid leakage in slurry transportation
Main Causes
Suspended solid particles repeatedly impact and scratch the diaphragm; sharp catalyst residue pierces thin diaphragm.
Solutions
Add chemical anti-corrosion filter at the inlet; upgrade thickened anti-wear diaphragm; reduce air pressure to lower particle impact force.
Fault 7: Flange corrosion and toxic medium seepage
Main Causes
Chemical liquid erodes sealing gaskets; long-term vibration loosens flange bolts; uneven locking force causes sealing gaps.
Solutions
Replace corrosion-resistant PTFE gaskets; fasten bolts diagonally; regularly inspect hazardous chemical interfaces.
Fault 8: Insufficient discharge pressure under high back pressure
Main Causes
Overlong chemical pipeline, excessive elbows and closed reaction kettle valves increase back pressure; unreasonable air pressure setting leads to insufficient power.
Solutions
Simplify pipeline layout and reduce flow resistance; appropriately increase air pressure within the rated range; install buffer tank to stabilize back pressure.
6. Service Life Law of Chemical Pump Wearing Parts
Rubber Sealing Accessories: 1~3 months in organic solvent; 3~6 months in salt crystallization liquid; the fastest aging and vulnerable parts.
Diaphragm: 6~12 months for clean chemical liquid; only 2~4 months for particle-containing slurry.
Valve Ball and Valve Seat: 8~12 months; easy to wear and deform under long-term particle impact.
Pneumatic Components: 1.5~2 years; susceptible to moisture rust in humid chemical workshops.
Pump Housing: 2~5 years; directly scrapped once corroded and delaminated.
7. Common Misoperations in Chemical Industry
Universal use of one pump for acid, alkali and solvent without material replacement;
No filter installed for slag-containing chemical liquid;
Long-term retention of residual chemicals inside the pump without flushing;
Excessively high air pressure pursuing large flow to accelerate component fatigue;
Uninsulated transportation of crystallizable liquid in low-temperature workshop;
Improper grounding leading to static accumulation of flammable solvent.
8. Chemical Safety Operation and Hierarchical Maintenance Specifications
8.1 Daily Safety Maintenance
Discharge accumulated water of air filter; neutralize and flush residual chemicals inside the pump; check flange leakage and static grounding condition.
8.2 Weekly Disassembly Maintenance
Disassemble valve group to clean crystal sediment and adhesive chemical dirt; inspect sealing ring swelling and surface corrosion.
8.3 Monthly Deep Inspection
Detect diaphragm pinholes and fatigue cracks; fasten all connecting bolts; replace aging vulnerable parts in advance.
8.4 Seasonal Anti-risk Maintenance
Insulate crystallizable liquid pipelines in winter to prevent freezing blockage; enhance ventilation and cooling for volatile solvents in summer to avoid air blockage.
8.5 Long-term Shutdown Preservation
Completely neutralize and clean corrosive liquid; dry internal moisture and seal the inlet and outlet; store separately in anti-corrosion and explosion-proof cabinet.
9. Working Condition Optimization and Upgrade Solutions
Volatile solvent working condition: Add exhaust valve and pressure relief pipeline to eliminate air blockage.
Crystallized salt medium: Equip electric tracing band and automatic flushing system.
Strong corrosive hazardous chemical: Adopt integral all-PTFE anti-corrosion pump.
Organic solvent batch production: Upgrade all FKM fluororubber sealing combination.
High-viscosity resin liquid: Optimize large-diameter flow channel and reduce running air pressure.
Toxic leakage-proof working condition: Use sealed flange and anti-corrosion metal hose to prevent liquid splashing.