Closed centre valves can be used with fixed displacement pumps whereby excess flow is bypassed from the pump output under the action of a spring loaded valve that senses the pressure drop between the pump and the load pressure. This cre­ates a pump pressure that is about 20 bar above that of the load that provides the efficiency benefits from bleed off control. This also provides pressure compensa­tion and thus avoids the load sensitivity obtained from central bypass valves.

For use in circuits where several actuators are to be controlled valves are available in which load sensing can be incorporated to operate the bypass valve using a pilot signal from the highest load pressure.

Such a circuit is shown in Figure 1 in which individual pressure compensa­tors are included to maintain constant flow through the valve that is supplying the actuator that is at the lowest pressure. The highest load pressure is sensed by the check valves and passed to the bypass-regulating valve, the opening of which is such as to deliver the flow required by both valves.

Such a circuit is shown in Figure 1 in which individual pressure compensa­tors are included to maintain constant flow through the valve that is supplying the actuator that is at the lowest pressure. The highest load pressure is sensed by the check valves and passed to the bypass-regulating valve, the opening of which is such as to deliver the flow required by both valves.

Figure 1. Pressure Compensated Bypass Valve with Load Sensing  

The valve can be used to supply several actuators and, providing the pump flow is adequate, the flow to any selected service will not vary with changes in the required outlet pressure, i.e. it is not load sensitive. When the load sensing pilot pressure exceeds the setting of the relief valve it will open and the resulting flow will depress the pilot pressure on the bypass valve causing it to open so that the system flow is reduced and, hence the pressure.