Wrapping up the operating envelope

Different scenarios

Suppose we had to design the system with the load and speed values while the cylinder was retracting. The exact same formulas could be used. However, the cylinder ratio would be inverted, to 3÷4, and the calculated area would be the annular, rod-end area. In the interest of space, that situation will not be evaluated here.

Many more situations and scenarios can be investigated by manipulating the VCCM equation but will not be explored here. For example, we may desire a sub-optimal design strategy that produces lower pressure drop at the design point, or that uses a non-symmetrical (valve ratio does not equal one).

Some interesting performance enhancements can come from non-symmetrical valve ratios. One very important one is that large over-running loads can be accommodated without cavitation and without any sacrifice in control or efficiency.

My intent has been to introduce the power and flexibility of having valve coefficients for our valves instead of the conventional industry practice of publishing the rated flow. K_Vis a property of the valve. Each land or orifice in the valve has a K_Vvalue, even when the valve is sitting on the shelf. Rated flow, on the other hand, is something that the valve exhibits only when it is operated at precisely the flow rating pressure of the valve.

In the real world, this essentially never happens. Contributing to confusion are the two different standard flow rating pressures — one for servovalves and one for proportional valves. When we know the valve coefficient, we can calculate the flow under any conditions, not just at rated pressure.

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