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Superior Relief Valve Options

Supplier: Custom Fluidpower
10 July, 2007

Fundamental to all hydraulic systems is the requirement of a relief valve, and in many systems there may be more than one to provide pressure control.

Sun Hydraulics provides a range of options superior to those of other manufacturers and includes valves with many special features.

Often we can overlook the use of a more suitable valve as we become conditioned to the use of the old but ever reliable RPEC and RDDA models.

Both these pilot operated and direct acting cartridges will, in a large majority of applications be more than suitable however, in many applications we may have issues that require a little more consideration to ensure a reliable system for our customers.

Beyond these standard products Sun manufactures some very specific relief valves and some units that allow flexibility. It is also important to remember that these cartridges suit standard Sun cavities.

Here is a few of the many available options.

Fast Acting ( Rapid Response )     

These pilot operated valves relief cartridges are used to protect system components against damage from pressure spikes and surges caused by rapid shifting of hydraulic control valves. The typical response time is 2 milliseconds. These valves are not designed for continuous duty operation.  Models include RPEE, RPGE…etc.

Soft Start (Soft Shift )                     

This model of pilot operated valve will also protect system components and is ideally used in areas of sudden load changes. Applications involving quick reversal of actuators including hydrostatic drives are well suited. The ramp profile of the controlled pressure rise can also be included in system designs. Models include RPET, RPGT…etc.


This type of relief valve is used to unload a hydraulic circuit completely once the set pressure has been reached. Once the cartridge opens it will remain open at 5 to 15 bar , depending on model, until flow through the valve has reduced to zero. At this point the cartridge will re-seat. The valve is effectively a circuit breaker.
Recent applications utilizing this valve include bore pump drives where the small engine driving the hydraulic pump is left unattended for days.
The valves were included to offset any problems when the borehole pump stalled in operation allowing the pump to run unloaded until engine fuel ran out. Models include RQIB , RQKB …etc.

Additionally to these type of relief valves are air controlled,ventable,pilot capacity and electro-proportional to name a few. Sun also now have a number of multi-function cartridges with both the relief function and check valve included in the one assembly.

When starting the design process or assisting our customers with a relief valve solution it is worth remembering just how much Sun has to offer in this very basic function that is applied to all hydraulic systems.

Fluid Compatibility.                   
Recently there have some inquiries concerning fluid compatibility with Sun cartridges.
Sun document this in saying that the fluid should be checked against the many o-ring manufacturer handbooks.
As standard Sun produce cartridges with both Nitrile seals and Viton (Fluorocarbon) seals. Viton is typically used in high temperature applications.
If the seal manufacturer supports the use of either material with the proposed fluid then there is no problem.

In some applications it may be necessary to change the cartridge seals to suit the fluid. This is also satisfactory however it should be noted that many cartridges include seals which may not be visible or accessible. Sun does not support the disassembly of their products.

In these instances it may be necessary to have Sun produce the cartridges with the correct seals factory fitted.

Click here for the complete publications http://www.parker.com/O-rings

Custom Fluidpower is the exclusive Australian Distributor of Sun Hydraulics.  For more information phone 1300 781 178 or visit www.custom.com.au or www.sunhydraulics.com.