A solenoid controlled relief valve (also called a solenoid operated relief valve) combines a pilot-operated relief valve with a solenoid directional valve. This allows remote electrical unloading of system pressure or selection between different pressure settings without extra external piping. It is a practical solution for protecting hydraulic circuits while improving energy efficiency and control flexibility.

What Is a Solenoid Controlled Relief Valve?

These valves integrate a conventional pilot-operated relief valve with a solenoid-operated directional valve mounted directly on the relief body and connected to the vent port.

Under normal conditions the valve limits maximum system pressure by dumping excess flow to tank when the set point is reached. The solenoid adds remote electrical control. Energising or de-energising it can vent the pilot stage (unloading the pump at low pressure), restore the relief setting, or switch between multiple pressure levels when remote pilot valves are connected.

This design removes the need for separate tubing between the relief and directional valves, reduces potential leak points, and supports both simple unloading circuits and more complex multi-pressure systems.

Why These Valves Matter in Industrial Hydraulics

Solenoid controlled relief valves deliver several practical advantages:

1. Remote unloading of fixed-displacement pumps, cutting heat generation and energy use during idle periods
2. Compact integration that simplifies manifold and power-unit layouts
3. Ability to select one, two or three pressure settings plus vent using single or double solenoids
4. Faster response for starting/stopping motors or controlled deceleration of actuators
5. Easy integration with PLCs, pressure switches and automated machine controls
6. Reliable over-pressure protection for pumps, cylinders, motors and lines

They are commonly used in hydraulic power units, presses, machine tools, material-handling equipment and industrial automation systems where both safety and efficient operation are required.

How a Solenoid Controlled Relief Valve Works

The valve uses a two-stage design. System pressure is sensed at the inlet. A small pilot flow controls the main stage (balanced piston or poppet). When inlet pressure reaches the spring-adjusted setting, the pilot opens, unbalancing the main stage so it lifts and routes flow to tank.

The solenoid directional valve sits on the vent port. When the solenoid vents the pilot chamber to tank, the main stage opens at very low pressure and the pump unloads. When the solenoid blocks the vent, the relief function returns to its set pressure. Different spool configurations determine whether the valve is normally vented, normally relieving, or capable of dual/triple pressure selection.

Back pressure on the tank line adds directly to the relief setting, so tank-line design must be considered. Some versions include a vent restrictor to soften the transition and reduce hydraulic shock.

Common Configurations and Options

Typical industrial versions (including those from major brands stocked by hydraulic specialists) offer:

1. Single-solenoid normally vented (energise to relieve) or normally relieving (energise to vent)
2. Double-solenoid options for dual or three-pressure selection
3. Sub-plate or threaded mounting
4. Flow ratings commonly from 100 L/min to several hundred L/min depending on size
5. Maximum pressures often in the 210–350 bar range
6. AC or DC coils with various connector styles
7. Optional high-venting or vent-restrictor versions for faster or smoother response

Cartridge-style versions are also available for compact manifold systems.

Step-by-Step Selection and Application Guide

1. Determine the maximum system pressure and required relief setting. Choose a valve whose adjustable range covers the working pressure with suitable margin.
2. Calculate the peak flow that must be relieved so pressure rise at full flow stays acceptable.
3. Decide the control logic needed: simple unload/load, dual pressure, or multi-pressure selection. Match the solenoid configuration accordingly.
4. Confirm electrical requirements (voltage, connector type, duty cycle) and environmental conditions.
5. Select the mounting style (sub-plate, threaded or cartridge) that suits the manifold or power-unit design.
6. Account for tank-line back pressure and, if needed, specify a vent-restrictor model.
7. Install with clean fluid, proper filtration and correct torque. Set the pressure at operating temperature and verify solenoid response.
8. Integrate the solenoid signal with the machine control so unloading occurs during idle periods and pressure is restored only when work is required.

Practical Application Tips

1. Use a normally open (vented) version with fixed-displacement pumps so the pump unloads whenever the machine is not performing work. Energise the solenoid only when actuators need pressure.
2. In hi-lo pump circuits the valve can unload the high-volume pump once system pressure reaches the low-pressure threshold.
3. For soft starting of large motors or controlled deceleration of loads, a normally closed version switched by a limit switch or timer can create a useful pressure ramp.
4. Keep the tank line short and adequately sized. Excessive back pressure raises the effective relief setting and can cause instability.

Frequently Asked Questions

What is the difference between a solenoid controlled relief valve and a standard relief valve?

A standard relief valve is purely mechanical and continuously set. A solenoid controlled version adds remote electrical unloading or multi-pressure selection without extra piping.

Can it unload a fixed-displacement pump?

Yes. This is one of the most common uses. Venting the pilot stage returns pump flow to tank at low pressure, reducing heat and power consumption.

Do these valves need special fluid cleanliness?

They perform best with clean fluid. Contamination can affect the pilot orifice and solenoid spool. Maintain proper filtration.

How fast do they respond?

Response is typically measured in tens of milliseconds. A slight delay is normal and usually only noticeable on very fast cycles.

Are different brands interchangeable?

Mounting interfaces, cavities and performance data vary. Always verify compatibility before substitution.

Conclusion

A well-chosen solenoid controlled relief valve (or solenoid operated relief valve) provides both reliable over-pressure protection and convenient electrical control of unloading or multi-pressure operation. By integrating the directional solenoid directly on the relief body, system designers eliminate extra piping, improve reliability and enable more efficient fixed-pump circuits.

When specifying these valves, match flow capacity, pressure range, solenoid configuration and mounting style to the actual duty cycle. Proper selection and installation deliver safer operation, lower energy use and longer component life in industrial hydraulic systems.

Author Bio

Fluid Force Technical Team

Fluid Force supplies industrial hydraulic components including manifold blocks, power units and branded valves and accessories. The team supports customers with practical selection guidance and reliable solutions for hydraulic system design and maintenance.