变量柱塞泵的压力油经泵体、泵壳变量壳体中的通油孔通过单向阀进入变量壳体的下腔，当拉杆向下运动时，推动伺服活塞向下移动，伺服阀的上阀口打开，变量壳体下腔的压力油经变量活塞中的通油孔进入变量壳体上腔，由于上腔面积大于下腔，液压力推动活塞向下运动，带动销轴使变量头绕钢球中心旋转，改变变量头的倾斜角（增大），柱塞泵的流量随之增大。反之拉杆向上运动，变量头的倾斜角向相反方向变化，泵的流量也随之变化。当倾斜角度变至零以后，则变量头向负偏角方向变化，液流产生换向，泵的进出油口变换。
The pressure oil of the variable displacement piston pump enters the lower chamber of the variable displacement housing through the through-hole of the pump body and the pump housing through the one-way valve. When the pull rod moves downward, the servo piston is pushed downward, and the upper valve port of the servo valve is opened. The pressure oil from the lower chamber of the variable piston enters the upper chamber of the variable housing through the oil hole in the variable piston. Because the area of the upper chamber is larger than that of the lower chamber, the hydraulic pressure pushes the piston The downward movement drives the pin shaft to rotate the variable head around the center of the steel ball, and changes the tilt angle of the variable head (increase), and the flow rate of the plunger pump increases accordingly. On the contrary, when the pull rod moves upward, the tilt angle of the variable head changes in the opposite direction, and the flow rate of the pump also changes. When the tilt angle changes to zero, the variable head changes to the direction of negative deflection angle, the liquid flow changes direction, and the inlet and outlet of the pump change.