Diagnosing problems with valves in hydraulic diaphragm airless paint sprayers.

Hydraulic diaphragm airless paint spray machines are usually fairly basic simple machines with not much to go wrong. Unlike piston airless paint sprayers the valve action in diaphragm airless sprayers is much more passive and susceptible to problems that may not ordinarily affect piston pump.

A piston airless paint spray may effectively continue to operate using only one of the two valves commonly found in piston airless paint sprayers and enable the operator to complete a job.

On the other hand a hydraulic diaphragm airless paint spray machine will rarely operate effectively unless both inlet valve and outlet valve are operating correctly.

A quick way to check the outlet valve on a hydraulic diaphragm airless spray machine, assuming the machine will prime and pressurise, is to prime the machine with water or paint and then pressurise at a low pressure approximately 500 psi or lower. Stop the motor and watch the pressure gauge, if the valve is sealing the pressure should remain in the machine as indicated on the pressure gauge when the motor was stopped.

If the pressure drops away quickly and the bypass or relief valve is not leaking, then there is a problem with the outlet valve in your diaphragm airless paint spray machine.

Checking the inlet valve on a diaphragm airless paint pump usually requires removal of the valve from the machine. With the inlet valve removed visually check the inlet valve poppet and the seat for any cracks, chips, wear, pressure tracking or for any foreign objects preventing the inlet valve from opening and closing correctly.

With the inlet valve removed it is usually best to remove the outlet valve and also check for wear, cracks, chips, broken components or foreign objects preventing the outlet valve from operating correctly.

Many airless spray service technicians will place their mouth over the airless spray inlet valve in reverse and attempt to blow back through the valve with the valve closed. If the valve can be blown through in reverse there is a leak which must be rectified.

Occasionally with hydraulic diaphragm airless paint sprayers even though both inlet and outlet valves do not appear to have any faults fitting of a new valve may allow the machine to once again function as expected.

Occasional unexplained faults such as this may even extend to pressure control valve or even hydraulic components in hydraulic diaphragm airless paint sprayers where to all appearances parts and components appear okay, yet replacement with another part eliminates the problem.

This may be due to the fact that the pumping action of hydraulic diaphragm airless paint sprayers is nowhere near as positive as the pumping action of a piston airless paint sprayer.

A bypass relief valve or prime spray valve as it may be referred to should always be either open or closed. In the closed position there should be no fluid returning through the bypass hose. If material continues to flow from a bypass valve in a hydraulic diaphragm airless paint spray machine with the relief valve closed the valve should be replaced.