Pressure-reducing valves (PRVs) maintain secondary, lower pressures in branches of hydraulic systems. (Upstream primary system pressure is still dependent on the system relief valve or alternative pressure-setting apparatus ) Pressure-reducing valves are usually open, 2-way valves that permit system stress fluid to flow through them until a set pressure is attained downstream. Then they change to throttle flow to the branch.
Pressure-reducing valves are actuated by forces exerted by stress. These forces set the desired operating pressure by producing a pressure drop across the valve's spring-biased principal spool. A pressure-reducing valve is not an on-off device: the place of its primary spool adjusts continuously to keep the desired pressure setting. Of all pressure-control valves, pressure-reducing valves would be the most sensitive to contamination-related malfunctions.
A pressure-reducing valve can malfunction in a variety of means. To troubleshoot a pressure-reducing valve, then refer to Figure 14 and install pressure gauges to examine inlet pressure at test port TP1 and socket pressure at test port TP2. Use these readings to test:
Decaying set stress (low pressure at port TP2). If pressure at the outlet port drops under the desired set pressure, then check the pilot head bolt and chair for excess wear that might allow increased drain flow. Excessive drain flow through this segment of this valve reduced the pressure required in the chamber above the main bolt to improve valve pressure fall and restrict operating pressure at the division circuit.
The valve won't hold reduced-pressure placing (high pressure studying at vent TP2). If preset pressure exceeds desirable values, check for a:
Plugged pilot drain line which would boost pressure in the room above the main spool, allowing primary system pressure fluid to flow into the division circuit.
Or the main spool is trapped in the open position because contaminants are wedged between the spool and its bore.
Or the major bolt or bore is scored, or possibly both are scored.
The valve cannot be adjusted to the desired low-pressure setting (high-pressure reading of interface TP2). If the valve Cannot Be corrected to some desired pressure setting following the adjustment knob has been turned to its closed or almost closed position, check for:
Spool or bore wear that would enable main system pressure fluid to flow to the branch circuit, or
A broken spring in the pilot mind, leading to inadequate spool-to-seat force from the hands head.
Fluctuating pressure or no pressure in output port (zero pressure reading at vent TP2). If there appears to be no fluid pressure in port TP2, check to determine if:
The principal spool is stuck closed, allowing no pressure liquid to flow into the branch. This condition can result from contaminants preventing the orifice in the passage connecting the two ends of the primary spool, bothering the hydraulic equilibrium between the pilot stresses in the lower and upper control chambers.
The principal spool is stuck closed because of contaminants or scoring of this spool, its own bore, either or perhaps both.