In reviewing the different pilot operated functions, you will discover that no matter what the design or desired function, pilot operation always works on the principle of creating either balanced or unbalanced pressure conditions across the main control element.
More specifically, in relation to pilot operated pressure reliefs, you should know what is meant by the terms remote piloting, venting, and high vent option. You should also understand the three uses of the external pilot drain: for more stable pressure adjustments, for remote pressure control, and for load sensing.
The important points covered in our discussion of pressure reducing valves were: first, the relieving ability of a pressure reducing valve, and, second, the differences between pilot operated versions with either primary or secondary control. We also mentioned the inherent ability of the reducing valves to generate heat in the hydraulic system.
In addition to your knowledge of relief and reducing functions, you should also have a good understanding of the versatility offered by the multi-function family of direct and pilot operated valves. You should know the assembly variations and application requirements in using the valve in sequence, counterbalance, overcenter counterbalance, or unloading functions. In addition, you should realize the special requirements of accumulator circuits.
The hydraulic specialist, who understands pressure and how to control it, knows just about half of everything there is to know in his field. When he combines this knowledge with the principles of flow, the designer has the world of hydraulics at his fingertips. section 3 will deal with flow and its relation to speed in the hydraulic system.
Wednesday, September 19, 2007 1:34