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. KVis a property of the valve. Each land or orifice in the valve has a KVvalue, 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.

Handbook serves electrohydraulic system designers



The fourth edition of the Designers’ Handbook for Electrohydraulic Servo and Proportional Systems contains more useful information than the third edition, which has become the defacto Bible for electrohydraulics technology. Learn:

• how to calculate and control pressure losses in plumbing, subplates, and manifolds,
• how to analyze and control a variety of mechanical loads, including conveyors and belts and triangulated loads,
• valve dynamic properties and how to include them in your system,  
• electronics, especially transducers and signal conditioning, and
• mobile equipment electrical systems, including batteries and charging systems.

The textbook contains 786 pages and sells for $159. To order, visit our Bookstore. Print the PDF order form, fill it out, and mail, fax, or e-mail it to us.

Special offer for H&P readers: BOGO

Buy the Designers’ Handbook for Electrohydraulic Servo and Proportional Systems and get a copy of Basic Electronics for Hydraulic Motion Control for free. It contains extensive coverage of electronic feedback and control, with emphasis on hydraulics technology. This hardbound text is a must for anyone considering certification as a fluid power engineer.