Why we need the Innovation SHP?
Automatic recirculation check valves (ARC) type SSV are having a physical limit up to a differential pressure of approx. 180 bar. But the industrial developments of the last 10-15 years rises the pressure level more and more over this limit.
The internals inside the bypass branch have to reduce the pump pressure down to suction pressure. In valve type SSV this pressure reduction is divided into several steps of throttles. In the design of the bypass of the ARC type SSV the most important part is the so called “bypass valve head”. Its purpose is the control of the bypass flow and the complete closing of the bypass as well. As consequence this part is affected from heavy wear by cavitation after a long life span, when the pump works within its minimum flow-range.
Another problem is the high actuating force in the rotary valve at a high differential pressure. With the current type SSV you have to consider a fairly high switching point of the bypass is relatively high switching hysteresis as consequence. That means the closing point of the bypass is relatively high above the required min. flow.
Finally, the potential of higher spring force is limited, because it would lead to a higher pressure loss in main flow direction.
Research and development:
The most important development is a hydraulically controlled multistage throttle concept which allows a nearly cavitation-free work in the whole operating range of the pump resp. in the whole range of bypass flow rates. Nevertheless, the pump min. flow control is modulating, that means, just the necessary amount of fluid for pump protection is provided.
Additionally it avoids the critical “minimal opening” of the bypass which can cause heavy wear even in a multistage throttle, by closing the bypass from a certain point on.
And the switching hysteresis is minimized, too, because the bypass flow control device is hydraulically balanced and hydraulically actuated, so there is no friction to overcome and the actuating force comes out of the medium itself.