ABSTRACT
Both the second and third conditions can be due to contamination that hinders movement by scarring of the main poppet/pilot piston or their bores.
When using a pilot-to-open check valve the ratios of the pilot piston area to the cylinder areas associated with the pilot operated check valve must be correctly proportioned. The ratio between the pilot piston area and the main poppet in the valve must be greater than the ratio between the cylinder piston area and its annulus area in the rod end. A good condition would be for the cylinder piston annulus area to be 2:1 with the check valve area. The establishment of the proper check valve area ratio is the responsibility of the valve designer. The maintenance person needs to understand this area relationship when called upon to troubleshoot the circuit. Once the problem is isolated to be the pilot operated check valve the repair or replacement action must be taken.
