I have discussed the pressure control valve previously in my series on hydraulic schematics, but those descriptions were primarily focused on the symbology explanation and how the circuit symbol is drawn. I’m going to do a blog series on pressure valves, because covering all pressure valves in one go would make this missive longer than any of my full length articles.
A pressure control valve does exactly what its name implies; it controls pressure, which is the force density component of hydraulic energy. Flow is the other major piece of hydraulic energy, and is the time component of the equation, but it’s important to know they’re related more than just being two factors of a larger unit.
Controlling pressure doesn’t just control the amount of force or torque a cylinder or motor can create, but pressure also controls speed in two ways. Because higher force equates to faster acceleration, a hydraulic system with more pressure will have shorter cycle times, especially if the machine uses various actuators stopping and starting many times per minute. Because Acceleration equals Force divided by Mass, the more force (pressure) you apply to the same mass, the faster it will accelerate. Acceleration is often overlooked in hydraulics, and with rapidly cycling actuators, it can eat up a lot of work time.
The other way in which more pressure increases speed is because higher pressure can give you higher pressure drop, or more pressure potential, if you will. If there are any components, such as valves, tubes, hoses, etc, which limit flow enough to create significant backpressure, you could be in a situation where higher pressure means higher flow. Without getting into unneeded complexity related to servo systems or constant pressure pumps, just understand that higher upstream pressure across any restriction means you will have higher flow.
The most straightforward result from an increase in pressure, however, is generally an increase in force. So most often when we speak of pressure control, we’re referring to the control of force, be it the control of force from pilot pressure working upon main-stage valve spool, or the torque output of a wheel drive motor. In the upcoming blog series, I’ll discuss the various common pressure control valves and their applications. Don’t wear out the edge of your seat in the meantime.