# How to model a Combination Pressure Reducing Valve (PRV) and Pressure Sustaining Valve (PSV)

 Product(s): WaterGEMS, WaterCAD Version(s): CONNECT Edition, V8i Area: Modeling

# Problem

How to model a Combination Pressure Reducing Valve (PRV) and Pressure Sustaining Valve (PSV)?

How do a model a PSV and PRV in series which controls both the upstream and downstream pressure?

# Solution

### Application and Benefits

• To maintain a minimum upstream and maximum downstream pressure or hydraulic grade.
• This valve may be helpful when there is an upstream water source and a pump at a high elevation that distributes to a network at a lower elevation.
• When an upstream pump shuts off, this valve would prevent the upstream network from emptying.
• PRVs and PSVs can be modeled to use either hydraulic grade or pressure settings.

### Example of this Valve

Cla-Val Model 692-01 Combination Pressure Reducing and Pressure Sustaining Valve

### How to model

This can be modeled with a PSV and PRV in series with the correct orientation and HGL settings. Since this can be very difficult to solve hydraulically, you may need to select the "2.00.12" version of the solver in the "Engine Compatibility" calculation option, and introduce a "leak pipe" to help with the hydraulics as described in this article: Ill-conditioning User Notification for valves in a hydraulic model

Note that the PSV and PRV elements do not attempt to "set" the pressure to the exact values that you enter but rather the PSV maintains the upstream pressure to be equal to or greater than the setting and the PRV maintains the downstream pressure to be less than or equal to the setting. It may be possible in some cases for multiple solutions to exist for a combination PSV/PRV. Meaning, one valve or the other could be partially closed (throttling to induce the necessary headloss) to meet the same constraints. It is also possible in some cases for both settings to be physically impossible to maintain at the same time, so care must be taken to configure the arrangement properly.

Note that in some cases it may not be physically

### Example of how to model

The following example model can be opened in the CONNECT Edition or V8i SELECTseries 6 of either WaterGEMS, WaterCAD, or HAMMER.

combination PRV PSV example.zip

### Video

The above video is simulating a pump shut down.

Stage 1: As the upstream hydraulic grade decreases to 20ft (PSV's minimum hydraulic grade setting), the PRV gradually opens to maintain a downstream hydraulic grade of 10 ft (PRV's maximum hydraulic grade setting).