A pressure reducing valve controls and regulates the pressure downstream of the valve. 


  1. Open the Set Control Data dialog as described in the previous section.


  1. Click the pressure reducing valve (PRV) radio button.


  1. Type the name of the pressure reducing valve in the Control Name field.


  1. Type the required reduced pressure in the Set Pressure field.


  1. Enter the allowable differential pressure range for the valve operation if appropriate.


  1. Click OK to add the pressure reducing valve to the pipe.


NOTE: The pressure reducing valve (PRV) introduces an additional pressure loss in the pipe to control the downstream pressure at the end of the pipe to the value specified by the user. The additional pressure loss across the control valve is reported in the results tables.


A PRV can operate under three different conditions: (1) regulating, (2) fully closed, and (3) fully open. How the valve operates depends on the defined set pressure value for the valve. The fully open and fully closed positions represent the extreme operations of the valve. Each of the valve positions is described below: 


(1) Regulating         The valve maintains the downstream pressure to the set value by introducing a pressure loss across the valve, thus throttling the flow rate through the PRV.


(2) Fully Closed This mode of operation occurs if the valve’s set pressure is less than the pressure downstream of the valve for the case where the valve is closed. When this occurs in an actual pipe system, the flow through the PRV reverses and the PRV acts as a check valve, closing the pipe. In PipeFlow Expert, this method of operation is detected and reported but the system is not then solved for this scenario. The user must decide if this method of operation is what they intended and if so then they can close the pipe and continue to solve the system. 


(3) Fully Open          This mode of operation occurs if the valve’s set pressure is greater than the pressure upstream of the valve for the case where the valve is fully open. When this occurs in an actual pipe system, the PRV maintains a fully open position and it has no effect on the flow conditions (except to add a frictional loss through the valve). In PipeFlow Expert, this method of operation is detected and reported. But the system is not solved because the differential pressure across the valve would have to be negative, i.e. the valve would be acting like a pump rather than a pressure control. 



Pipe Flow Expert will only solve a system when the PRV is operating in Regulating mode.


AVOIDING PRV OPERATION PROBLEMS: In general, PRV operation problems can be avoided by finding the valve's pressure regulating range and specifying the valve’s set pressure to a value within this range such that the mode of operation is ‘Regulating’. First, solve the system without the PRV control and note the pressure at the node downstream of the pipe which previously contained the PRV. This is the maximum pressure the PRV can be set to (i.e. it is equivalent to finding the valve’s inlet pressure for the case where the valve is fully open). Secondly, solve the system after closing the pipe that contains the PRV and note the pressure at the node downstream of the closed pipe. This is the minimum pressure the PRV can be set to (i.e. it is equivalent to finding the pressure downstream of the valve for the case where the valve is fully closed).