STRUCTURE, FUNCTION, & MAINTENANCE STANDARD SELF PRESSURE REDUCING VALVE 2. When in neutral or load pressure P2 is low (When boom is lowered and arm is in IN position and they are moving down under own weight) Note: When load pressure A2 is lower than self-pressure reduc- ing valve output pressure PR. Valve (7) receives the force of spring (8) and PR pres- sure (which is 0 MPa {0 kg/cmІ} when the engine is stopped) in the direction to close the circuit between ports P2 and A2.
If the hydraulic oil flows in port P2, the φ dx P2 pressure becomes equal to the total of the force of spring (8) and the value of area of d x PR pressure, then the area of the pass between ports P2 and A2 is so adjusted that the P2 pressure will be kept constant above the PR pressure. If the PR pressure rises above the set level, puppet (11) opens and the hydraulic oil flows from the PR port through orifice "a" in spool (14) and open part of pup- pet (11) to seal drain port TS. Accordingly, differential pressure is generated between before and after orifice "a" in spool (14) and then spool (14) moves to close the pass between port P2 and PR.
The P2 pressure is controlled constant (at the set pressure) by the area of the oil pass at this time and supplied as the PR pressure. (See Fig. 2.) 3. When load pressure P2 is high If load pressure A2 rises and the pump discharge increases because of operation of the work equipment, the φ dx P2 pressure rises higher than the total of the force of spring (8) and the value of d x PR pressure, and then valve (7) moves to the right stroke end. As a result, the area of the pass between ports P2 and A2 increases and the pass resistance lowers and the loss of the engine power is reduced.
If the PR pressure rises above the set pressure, puppet (11) opens and the hydraulic oil flows from the PR port through orifice "a" in spool (14) and open part of puppet (11) to seal drain port TS. Accordingly, differential pressure is generated between before and after orifice "a" in spool (14) and then spool (14) moves to close the pass between port P2 and PR. The P2 pressure is controlled constant (at the set pressure) by the area of the oil pass at this time and supplied as the PR pressure. (See Fig. 3.) 10-84 PC210/240-7K