Rexroth logo

Why use pressure reducing valves?

Pressure reducing valves are critical for the safe, reliable and precise control of hydraulic equipment.

A pressure reducing relief valve is a safety valve that is used to control or limit the pressure in a system. Without using a correctly sized pressure reducing valve, the pressure might build up and create a process upset, instrument or equipment failure or fire.

This range of Bosch Rexroth pressure control valves addresses this by limiting the maximum amount of pressure in a hydraulic circuit. The relief valve is designed or set to open at a pre-determined set pressure to protect pressure vessels and other equipment from being subjected to pressures that exceed their design limits!

The difference between pressure reducing valves and pressure relief valves:

A pressure reducing valve will normally be closely fitted with a component that requires a pressure reduction. These valves are typically used in clamping and punching operations, where a clamping cylinder and punching cylinder both may be operated with same hydraulic pump.

  • Pressure reducing valves receive higher pressure at the inlet but it will deliver the pressure, according to pre-set requirements, on its outlet
  • Pressure reducing valves are normally set in an open position
  • Pressure reducing valves only feature one check valve to allow free flow in the reverse direction
  • Pressure reducing valves are be externally drained. They feature a separate drain line directly from valve to reservoir
  • Pressure reducing valves have one pilot line to sense the outlet pressure

A pressure relief valve will normally be fitted with the main hydraulic pump discharge line. Its main purpose is to monitor the hydraulic pressure in hydraulic pump discharge line, according to the requirement of pressure to operate the actuator.

  • Pressure relief valves are normally in a closed position and will only come in line once the pressure requirement increases and reaches the setting point of relief valve
  • Pressure relief valves have one pilot line to sense the inlet pressure
  • Pressure relief valves are internally drained as the outlet of relief valve will be connected with the reservoir

The difference between direct and pilot-operated valves:

Direct operation: direct-operated pressure reducing valves respond directly to variations in downstream pressure to provide the required flow and pressure to satisfy the system set point.

Port 2 opposes the balance force provided by the spring to determine the plug position. For direct-operated valves, port 2 is also considered the loading force. If port 2 increases, the spring is compressed and the plug moves upward towards the closed position to further restrict fluid flow. Any decrease in port 2 allows the spring to move the plug downward, opening the valve further and allowing more fluid to pass. The plug position in a direct-operated regulator responds immediately to any change in the port.

Pilot operation: pilot-operated pressure reducing valves consist of the same essential components of direct-operated units (plug and seat, diaphragm, spring) with the addition of a pilot which separates port 2 and the diaphragm loading force. By doing this, the loading force can be controlled in relation to changes in port 2. This enables the valve to be more responsive to condition changes.

This pilot operation requires an external sense line that is connected to the downstream piping. Measuring pressure further downstream allows for more accurate sensing of the true outlet pressure conditions. This pilot operation can simply and effectively be considered a second regulator, providing additional control to the main regulator, improving overall sensitivity and accuracy.

Contact Bosch Rexroth South Africa Group of Companies today on +27 11 975 9700 for more info or send us an enquiry and we will contact you!