Diagnosing problems with airless piston pump pressure valves.
Here is a way to test your piston airless spray pump to ensure the inlet valve and outlet valves, including the relief valve are functioning correctly.
This test is much easier to do and see the results with a large longer stroking airless piston pump compared to a small short stroke fast cycling piston airless sprayer.
A small airless spray tip that slows the output of the airless piston pump will make this test easier to read.