Pump unloading traditionally results in a significant pressure spike in the tank line, jeopardising the tank line components. The following depicts a typical pump unloading circuit - with the associated pressure spike resulting from hard switching:
Sun Hydraulics offers a 'Soft Shift' option for its economical solenoid operated directional valves. The soft shift option extends the shift times on these spool valves, which can greatly reduce the hydraulic shock generated when a pump is electrically unloaded.
Most 2-position, 2-way screw-in cartridge pilot solenoid valves use a poppet style construction to satisfy low leakage requirements. Sun Hydraulics has adopted a different approach that uses a precision spool/sleeve design. Available in both 2-position, 2 and 3-way pilot solenoid cartridges, this approach produces leakage characteristics equivalent to poppet style designs.
Since control volumes in pilot circuits are typically small, the lower gain characteristics of spool valves produce a softer unload. To further extend the operating rate, Sun offers a 'Soft Shift' option that adds an orifice in the valve's armature to gain greater control of fluid displacement. Combining the benefits of a spool valve with the 'Soft Shift' option extends shift times, which can reduce the hydraulic shock generated when unloading main-stage elements. Sun's 'Soft Shift' option is offered on all of its spool-type solenoid valves.
An example is Sun's DLDA-S, which is a direct-acting, solenoid-operated, 2-position, 2-way cartridge, balanced spool valve with a soft shift feature. The soft shift feature greatly reduces system shock due to valve actuation. The valve is available in either a normally open or normally closed configuration:
Sun's small pilot solenoid valves are used to unload larger main-stage elements remotely, or by directly integrating the pilot valve into the main-stage element. In this latter approach, unique to Sun, 12 different pilot valves (proportional, solenoid, hydraulic and pneumatic) can be integrated into a variety of main-stage elements.
For more information contact Axiom Hydraulics, +27 (0) 11 334 3068, www.sunhydraulics.com
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