Komatsu WB97R-5 S. When angle a of the swash plate increases, the difference between volumes E and F increases too, and this makes delivery Q increase accordingly. Angle a of the swash plate is varied by the servo piston (11).
Komatsu WB97R-5 S Service Manual. 2 - The servo-piston (11) moves in a reciprocating linear motion caused by pressure signals from the PC and LS valves. The linear motion is transmitted to the swash plate (7). The swash plate is supported by the pump body (8) through the ball (9), and this is the reason why the swash plate (7) moves in a semicircular alternate motion.
The LS valve controls the pump delivery according to the stroke of the control valve lever, i.e., in function of the delivery demands made by the actuators.
Komatsu Service Mnual. The LS valve detects the actuator’s delivery needs by means of the differential pressure DPLS existing between pressure PPLS (control valve input pressure) and pressure PLS (control valve output pressure). The sensing of this differential pressure permits control of the main pump delivery Q. (PPLS, PLS and DPLS are, respectively, the pump pressure, the Load Sensing pressure, and the difference in pressure between these two values).
Komatsu Workshop Manual. In other words, the LS valve detects the pressure difference DPLS generated by the passage of the oil flow through the surface freed by the control valve spool, and controls the pump delivery Q so as to keep the pressure drop constant. It can therefore be assumed that the pump delivery is proportional to the demands made known by the control valve.
Pump pressure PPLS (pump pressure at control valve input) and pressure PLS (Load Sensing pressure) are introduced into the LS valve. The relation between differential pressure DPLS and pump delivery varies as shown in the diagram on the right.
The PC valve performs an approximate power check, and ensures that the hydraulic horse-power absorbed by the pump does not exceed the horse power delivered by the endothermal engine. This is achieved by limiting the pump delivery Q in function of the delivery pressure PPLS, even if the LS valve requests an increase in delivery Q due to the larger section freed by the control valve spool, in the presence of high pressure pump delivery.
In other words, when during operation the delivery Q increases and the delivery pressure PPLS also increases simultaneously, the PC valve reduces the pump delivery Q. When the delivery pressure PPLS decreases, the PC valve increases the pump flow. As pressure PC increases, the relation between pressure PA and delivery Q is changed in accordance with the force applied by pressure PC.
In other words, when the force applied by pressure PC is added to the force applied by the pump's delivery pressure against the spool (5), the relation between pump delivery pressure and delivery is switched from "1" to "2" in accordance with increment "X".