OPERATION AND TESTING OF A PILOT OPERATED …

1 "A""B""C""A""B""C""A""B""C""A""B""C""A"" B""C"FIG. POWERSCHEMATIC SYMBOLFILENAME: AND TESTING OF A PILOT OPERATED CHECK VALVEA PILOT OPERATED ( PILOT TO OPEN ) CHECK VALVE WORKS LIKE A NORMAL CHECK VALVE, ALLOWING FREE FLOW IN ONE DIRECTION, WHILE STOPPING FLOW IN THE OPPOSITE DIRECTION. IN ADDITION THERE IS A PILOT PISTON THAT UNSEATS THE CHECK BALL AND ALLOWS FLOW IN THE OPPOSITE DIRECTION. THE FOLLOWING ARE STEPS WILL COMPLETELY TEST MOST PILOT OPERATED CHECK VALVES. THE FIGURES BELOW ARE NOT INTENDED TO SHOW THE CONSTRUCTION OF THE VALVE YOU ARE TESTING BUT THE BASIC OPERATING CHARACTERISTICS.

2 YOU MUST IDENTIFY WHICH PORTS ON YOUR VALVE CORRESPOND TO THE VALVE BELOW. "A" TO "B" IS FREE FLOW, "B" TO "A" IS BLOCKED FLOW, AND "C" IS THE PILOT OR "UNLOCK" PORT. FIGURE 1 SHOWS THE VALVE WITH NO FLOW AND THE CHECK BALL HELD ON IT'S SEAT BY A SPRING. FIGURE 2 SHOWS THE BALL LIFTED OFF IT'S SEAT BY FLOW ALLOWING FREE FLOW FROM "A" TO "B". FIGURE 3 SHOWS REVERSE FLOW BLOCKED BY THE BALL SEATED. IN FIGURE 4, PRESSURE IS APPLIED TO THE PILOT PISTON, LIFTING THE CHECK BALL FROM IT'S SEAT ALLOWING REVERSE THE VALVE1. APPLY PRESSURE TO "C" WITH "A" AND "B" OPEN.

3 THIS WILL TEST FOR LEAKAGE PAST THE PILOT PISTON SEAL. SOME VALVES HAVE NO PILOT PISTON SEAL AND SLIGHT LEAKAGE MAY FLOW IN "A". WITH "C" AND "B" OPEN. FREE FLOW SHOULD COME OUT "B" ( FIGURE 2 ). PRESSURE TO "B" WITH "C" AND "A" OPEN ( FIGURE 3 ). NO OIL SHOULD LEAK OUT "C" OR "A". OIL LEAKAGE MAY INDICATE A BAD SEAT OR PRESSURE STILL APPLIED TO "B", APPLY PILOT PRESSURE TO "C". "A" SHOULD STILL BE OPEN ( FIGURE 4 ). WHEN SUFFICIENT PILOT PRESSURE IS ACHIEVED, THE BALL WILL BE PUSHED OFF IT'S SEAT AND FLOW WILL COME OUT "A". NOW REMOVE PILOT PRESSURE AND THE BALL SHOULD RESEAT AND FLOW SHOULD STOP.

4 DO THIS SEVERAL TIMES TO ENSURE THE VALVE CAN REPEATEDLY UNSEAT AND RESEAT TEST. THIS TEST IS SET UP EXACTLY LIKE STEP 4. APPLY THE VALVES RATED PRESSURE ( OR THE CIRCUIT OPERATING PRESSURE IF KNOWN) TO"B" [EXAMPLE: 2000 PSI]. SLOWLY INCREASE PILOT PRESSURE UNTIL THE VALVE UNSEATS AND FLOW COMES OUT "A". IF PILOT UNLOCK PRESSURE IS 1/3rd OF "B" THE RATIO IS 3:1, 1/4th IS 4:1 AND SO ON.