Air operated diaphragm pumps are robust, but performance issues can still occur due to wear, installation conditions, air supply problems or changes in the pumped fluid.
Use the chart below as a quick fault-finding reference. It lists common diaphragm pump problems, possible causes and suggested actions to help operators and maintenance teams identify the next step.
If your pump issue is not listed, or if you need help selecting spare parts or a replacement pump, please contact our team.
| Problem | Cause | Solution |
|---|---|---|
| Pump cycles at stall or fails to hold pressure at stall | Worn check valve balls, seats or O-rings | Replace valve balls, seats or O-rings |
| Pump will not cycle, or cycles once and stops | Air valve is stuck or dirty | Disassemble and clean air valve, use filtered air |
| Check to see if the valve ball is severely worn and/or wedged in seat or manifold | Replace ball and seat | |
| Check to see if the valve ball is wedged into seat, due to over pressurization | Install pressure relief valve | |
| Dispensing valve clogged | Relieve pressure and clear valve | |
| Pump operates erratically | Clogged suction line | Inspect; clear |
| Sticky or leaking balls | Clean or replace | |
| Diaphragm (or backup diaphragm) ruptured | Replace diaphragms | |
| Restricted exhaust | Remove restriction | |
| Pilot valves damaged or worn | Replace pilot valves | |
| Air valve damaged | Replace air valve | |
| Air valve gasket damaged | Replace air valve gasket | |
| Air supply erratic | Repair air supply | |
| Exhaust muffler icing | Use drier air supply | |
| Air bubbles in fluid | Suction line is loose | Tighten |
| Diaphragm (or backup) ruptured | Replace diaphragms | |
| Loose inlet manifold, damaged seal between manifold and seat, damaged O-rings | Tighten manifold bolts or replace seats or o-rings | |
| Loose diaphragm shaft bolt | Tighten or replace | |
| Damaged O-ring | Replace | |
| Diaphragm shaft bolt O-ring damaged | Replace O-ring | |
| Pump cavitation | Reduce pump speed or suction lift | |
| Fluid in exhaust air | Diaphragm ruptured | Replace |
| Loose fluid side diaphragm plate | Tighten or replace | |
| Pump air valve freezes (talk to us about non-freezing air valves/exhaust) | Excessive moisture in compressed air | Install a dryer or hot air generator for compressed air. Alternatively, a filter may be used to remove the water from the compressed air in some applications |
| Pump exhausts excessive air at stall | Worn air valve block, O-ring, plate, pilot block, U-cups, or pilot pin O-rings | Inspect; replace |
| Worn shaft seals | Replace | |
| Pump leaks air externally | Air valve cover or air valve cover screws are loose | Tighten screws |
| Air valve gasket or air cover gasket is damaged | Inspect; replace | |
| Air cover screws are loose | Tighten screws | |
| Pump leaks fluid externally from ball check valves | Loose manifolds, damaged seal between manifold and seat, damaged O-rings | Tighten manifold bolts or replace seats or O-rings |
| Pump cycles but will not prime | Pump is running too fast, causing cavitation before prime | Reduce air inlet pressure |
| Check valve ball severely worn or wedged in seat or manifold | Replace ball and seat | |
| Seat severely worn | Replace ball and seat | |
| Outlet or inlet clogged | Unclog | |
| Inlet or outlet valve closed | Open | |
| Inlet fittings or manifolds loose | Tighten | |
| Manifold O-rings damaged | Replace O-rings | |
| Premature diaphragm failure | Cavitation | Enlarge pipe diameter on suction side of pump or move closer to the product |
| Excessive flooded suction pressure | Move pump closer to the product; raise pump/place pump on top of tank to reduce inlet pressure | |
| Misapplication (chemical/physical incompatibility) | Consult chemical resistant guide for compatibility for the products, cleaners and temperature limitations | |
| Incorrect diaphragm plates or plates backwards | Check operation manual for correct part installation | |
| Start up with full pressure | Recommend to start up pump slowly | |
| Unbalanced cycling | Excessive suction lift | For dry lifts or self-priming from dry, filling the chambers with liquid will prime the pump in most cases |
| Undersized suction line | Meet or exceed pump connections | |
| Pumped fluid in air exhaust muffler | Disassemble pump chambers. Inspect for diaphragm rupture or loose diaphragm plate assembly | |
| Suction side air leakage or air in product | Visually inspect all suction-side gaskets and pipe connections | |
| Check valve obstructed | Disassemble the wet end of the pump and manually dislodge obstruction in the check valve pocket | |
| Check valve and/or seat is worn or needs adjusting | Inspect check valves and seats for wear and proper setting. Replace if necessary | |
| Entrained air or vapor lock in chamber(s) | Purge chambers through tapped chamber vent plugs |
Global Pumps supplies air operated diaphragm pumps, spare parts and technical support for industrial applications across Australia. If you are dealing with repeated pump faults, reduced flow, air leakage, priming issues or worn internal components, our team can help review the application and recommend the next step.
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Head Office
12 Selgar Avenue Tonsley
South Australia 5042
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