This article was updated on November 10 with the solution to this challenge.
By Robert J. Sheaf, Contributing Editor
The advantage of using load-sense pumps is that they greatly reduce the pressure drop across flow control devices resulting in less heat buildup. The attached circuit is a good example of a simple cylinder circuit that incorporates a load-sense pump with a proportional valve.
The cylinder would push and pull fixtures in and out of a machine each cycle. Some fixtures required higher pressures to overcome breakaway friction. The hydraulics functioned well for months and then would only build pressure on the extend function but then only build 300 psi on the retract function. They switched the “A” and “B” connections at the valve but experienced the same low pressure on the retract function.
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If the external signal to the load sense control is vented to tank, the pump will compensate at the low load sense pressure of 300 psi. The ball inside the shuttle had been driven and jammed in the incoming signal side of the shuttle going to the rod side. They replaced the shuttle and installed small orifices in both lines going into the shuttle to soften the shifting speed of the ball in the shuttle.
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