Comparison of the C20 and C60 Pressure Regulating Valve Designs

Wanner™ is a manufacturer of sealless positive displacement pumps, most notably the Hydra-Cell^® Pro, encompassing a flow range from a fraction of a GPH to over 150 GPM at pressures from 30 to 5000 PSIG. Pressure regulating valves are a natural accessory for Hydra-Cell^® Pro Pumps to ensure the downstream pressure does not exceed the pump or system design pressure. In this article, we will compare and contrast the two different pressure regulating valves manufactured by Wanner Engineering: the C20 series and the C60 series.

 

Pressure Regulating Valve Design

Pressure regulating valves are used in conjunction with positive displacement pump systems to prevent the discharge pressure of the pump from exceeding the desired maximum discharge pressure. The pressure regulating valves manufactured by Wanner have three ports: an inlet, outlet and bypass. The inlet and outlet port are 180 degrees apart or “in-line” with each other while the bypass port is offset 90 degrees. The valve itself may be installed in a horizontal or vertical section of piping. The standard flow path is through the inlet and out the outlet with little to zero liquid flowing through the bypass port.

 

Within the valve body a plunger is pushed against a valve seat, forming a metal-to-metal seal and thus preventing liquid flowing through the bypass port. The plunger is pressed to the valve seat due to spring tension acting against the plunger. If the system pressure is high enough, the “spring” compresses and the plunger lifts off the seat, allowing liquid to exit through the bypass port.

 

The key difference with pressure regulating valves is that the plunger lifts off its seat only enough to bypass excess flow and maintain the maximum set pressure. Although the terms pressure “regulating” and “relief” valves are used interchangeably, a relief valve typically implies that it fully opens upon reaching the set pressure to enable complete liquid bypass.

 

Another design aspect related to Wanner’s pressure regulating valves is that all but one model uses stacked “spring discs” (a slightly concaved washer) to form spring tension and not actually a spring. This design provides steadier pressure adjustment and increased longevity. The pressure range can be changed by stacking the number of washers, stack order and thickness.

 

The C20 series PRV was Wanner’s initial PRV design and the C60 series is an improved design introduced a little over 20 years ago.

 

Both C20 and C60 PRVs provide an adjustable pressure range, immediate response to changes in pressure and a chatter-free bypass of flow.

 

The C20 series PRV uses o-ring style seals on the plunger to prevent leakage into the top section where the compressed washers are stacked (⓼,⓽). Over time these seals wear due to cycling frequency and abrasiveness of the liquid pumped with the resulting leakage weeping out the top of the valve.

 

Likewise, the plunger and valve seat will eventually wear and result in liquid leaking through the bypass port.

 

The plunger and valve seat are available in erosion resistant materials to extend their wear life. High pressure water systems might benefit from oversizing the pump flow rate by about 10% and thus the plunger is always slightly lifted off its seat, reducing the metal-to-metal contact (wear) and at the same time dampening the pressure spike associated with the plunger lifting off the seat. For abrasive liquids it is likely better to size the pump system to have no bypass during operation, leaving the PRV to react for upset conditions or the cyclical aspects of the application which cause changes in system pressure. An example might be a clogged spray nozzle which would result in higher pressure.

 

PRVs have an oversized valve body to minimize pressure drop and thus wear from abrasive liquids passing through the valve. Even so, when the liquid is very abrasive, it might be prudent to install the valve “off-line”. Installing the PRV off-line entails placing a tee fitting in the discharge pipe, plumbing the topside of the tee to the inlet of the PRV and plugging shut the PRV outlet. In this arrangement the liquid only flows through the valve when the system pressure exceeds the set pressure.

 

Wanner’s C60 PRVs operate on the same basis as the C20 series, the design difference is related to the plunger seal as well as overall increased simplicity (less components) to wear/replace.

 

Comparing the component illustrations for both PRV valve styles you can see that the basic designs are the same, with exception to the diaphragm style seal and plunger guide is integral to the plunger itself, reducing the number of components.

 

The diaphragm seal is definitely an improved sealing method, similar to the diaphragms used in Hydra-Cell Pro Pumps, the diaphragm has a built-in convolute which enables the diaphragm to rise and fall with the plunger. The convolute eliminates fatigue-type wear. Since the circumference of the diaphragm is sealed between the upper and lower portions of the PRV body (a static seal), the abrasiveness of the liquid does not cause wear that results in leakage. With the C20 series, hard particulate can get in-between the o-ring seal and plunger guide sleeve, damaging the o-ring.