Visual judgment: check that the plunger surface is smooth without wear marks. The more surface marks, the more serious the wear;
Sliding test: clean the plunger coupling with diesel or kerosene to make the coupling 45 degrees from the horizontal, and then extract one-third or more of the plunger Half of it is loosened again, and the plunger slowly slides down with the help of gravity. If it is too fast, it means that the clearance is too large, and if it stops and gets stuck, it means that it is scratched locally.
Suction check: block the lower end with index finger, block the oil inlet and return holes with thumb and middle finger respectively, the plunger is at the maximum oil supply position, and pull out the column Half of the plug, if you feel strong suction or return to the original position immediately after loosening, it indicates that it is qualified.
Constant pressure inspection: check the time until the plunger pressure is relieved through a special trial platform under a certain pressure. A short time indicates poor sealing and a long time， It indicates that the sealing performance is good.