Machinery Lubrication magazine published by Noria Corporation
Issue link: https://www.e-digitaleditions.com/i/1275515
12 | July - August 2020 | www . machinerylubrication.com We have seen a lot of conf usion about pres- sure reducing valves and regulators in fluid power systems. is confusion is largely due to the nomenclature and partly because the schematic symbols are not always as intuitive as they could be. e valves themselves are actually fairly simple. In a pneu- matic system, the valve is called a regulator. In a hydraulic system, it is called a pressure reducing valve. Notice that the symbols are quite similar, because their function is the same, only with a different medium. In Figure 1, the two symbols are shown side-by-side. As in most fluid power pressure controls, the regulator and the pressure reducing valve are characterized by a single square with a single arrow drawn inside. We can see that the only difference between the two is that, in the pressure reducing valve, the arrowhead is filled in, whereas in the regulator there is only the outline of an arrowhead. is is to illustrate that the regulator is designed to control pressure in a gas medium while the pressure reducing valve is intended to operate with a liquid. Bot h of t he se va lve s a re normally open, which is indicated by the arrow touching both the inlet and the outlet ports. On the bottom of the symbol is a jagged line repre- senting a spring. If the spring is adjustable, a diagonal arrow will be drawn across it. A good way to think of the valve when tracing flow on a schematic is to consider the spring pushing the arrow up and holding the valve open. But, in order to reduce the pressure, the valve must close off to some degree. Notice the downstream pilot line. System pressure is measured downstream of the valve and applied to the top of the arrow, pushing it down and partly closing the valve. When the two forces equalize, i.e. spring tension on the bottom and air or hydraulic pressure on the top, a balance is achieved and the pressure is reduced. e air valve is called a regu- lator, but even though the name suggests that it can either increase or decrease the pressure, like the pressure reducing valve, it can only decrease the inlet pressure. In a pneumatic system, the regulator is the primary pressure control. The compressor will determine the maximum pressure and the regulator reduces the pressure to a level that is safe and usable, opening and closing as necessary to keep the pressure stable. While there may also be secondary regulators to lower the pressure further for use in branch circuits as shown in Figure 2, there will always be a primary regulator to stabilize and set the main system pressure. In a hydraulic system, pressure reducing valves are used to lower the system pressure for use in circuits that require less pressure than the maximum system pressure. This extends the life of the lower pressure circuits and conserves energy. Distinguishing Regulators and Reducing Valves HYDRAULICS Jack Weeks | GPM Hydraulic Consulting " The regulator is designed to control pressure in a gas medium while the pressure reducing valve is intended to operate with a liquid. "