Parker Valves: The Makers Of Hydraulic History
Parker valves are among the most respected, high-quality valves on the market. The company’s massive range of servo valves, which include simple solenoid valves and heavy-duty hydraulic valves, are vitally important to a wide range of motion control technologies and systems, particularly in the mobile, industrial and automotive industries.
The degree of Parker’s market domination is actually such that, should you encounter any machine that moves or calls for motion control, you would do well to assume that Parker valves play a vital part in some element of its functionality.
The term ‘servo’ comes from the original French term, ‘Le Servomoteur’, or ‘the slavemotor’, a term coined by J. J. L. Farcot to describe the workings of engines utilizing hydraulic or steam systems for ship steering. The term, however, can only be correctly applied to devices where feedback to the device assists in some way in controlling the positioning of the device. Generally, servos are used for position control – but the means by which they accomplish this are varied, including via the use of electric motors or a combination of electronics, hydraulics, pneumatics and magnetics (such as by the incorporation of solenoids or solenoid valves).
The guiding principle of Parker valves, and indeed, of servo valves in general, is that of negative feedback. By this principle, the control input or ‘intended’ position is by some method compared with the actual position of the mechanical system (as determined by feedback measured by some form of transducer, be that a sensor or an actuator). An example of this is cruise control systems in cars, which maintain the speed of a car, whether it be travelling uphill or down. Such systems first calculate groundspeed on the basis of driveshaft rotations, and using that as a guideline, vary the throttle position as required by use of solenoid valves. Thus the primary function of Parker valves and servos is error-correction in moving mechanisms.
Hydraulic valves, (which, these days, are usually more accurately describable as electro-hydraulic valves) are servo valves capable of continuously controlling hydraulic outputs as a function of some electrical input. Through the use of valves to control the quantity of a fluid released, they can control the force output of a device – and, because of the relative incompressibility of fluids, are preferable to pneumatic systems in a variety of situations. Indeed, the ability of such systems to speedily output high forces greatly outstrips most pneumatic systems, thus making hydraulics more appropriate for very heavy industry as well as situations in which high speeds on both concentric and eccentric manoeuvres are required. This often requires engineers of Parker valves and other hydraulic components to reinforce their creations to withstand greater force-feedback than pneumatic machines require – but, for the heavy work these machines can perform, the extra work is considered well worth it.
The incompressibility of hydraulic working fluids also reduces so-called ‘spring action’. The physical nature of fluids ensures that, the instant that hydraulic fluid-flow stops, the slightest motion of the load releases the pressure exerted on the machine, meaning that there’s no need to ‘bleed off’ pressurized fluid as there is in pneumatics.
