# Pressure Reduction Ratio Valves

Pressure reduction ratio valves can also be modeled by using the "User Defined Generic" node . The following example shows such a design case. It is intended to model a ratio pressure reducing valve in a water flow system at "Point B". The flow system has an inlet boundary pressure of 5 bar g and the valve ratio is 4:1. Note, it is important to set the relevant flow and pressure units for the valve and set the K Term and B Term Type to "Inlet Pressure". The exponent n and m can be left as 0. Figure 1 shows the data-entry for the valve. Figure 1: Data Entry for Pressure Reduction Ratio Valve (bar a reference pressure). The data-entry shown in Figure 1 is based on "bar a" (absolute) reference pressure at the valve inlet. The valve was modeled in the system shown in Figure 2. Figure 2: Modelling Pressure Reduction Ratio Valve (bar a reference pressure). The pressure at the inlet of the ratio pressure reducing valve is calculated to be 5.98 bar a (absolute) and since the reduction ratio is 4:1, the outlet pressure must be 1.495 bar a (5.98 / 4 = 1.495 bar a). We can see in Figure 2 this is the condition which has been solved based on the data-entry shown in Figure 1. If the pressure reference for the valve was "bar g", the data entry would appear as shown in Figure 3. Figure 3: Data Entry for Pressure Reduction Ratio Valve (bar g reference pressure). When we solve the valve using the conditions described in Figure 3, the inlet pressure in bar g units is taken into account, i.e., 4.963 bar g. The resultant pressure at the outlet of the valve is therefore, 4.963 * 0.25 = 1.241 bar g. Figure 4: Modelling Pressure Reduction Ratio Valve (bar g reference pressure).