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Modeling a 3-Way Valve

by Engineered Software, Inc.

PIPE-FLO does not have a native 3-way control valve. However, the functionality of a 3-way control valve can be modeled using either of two ways. Both consist of using two Flow Control Valves in conjunction.

To model a 3-way valve in PIPE-FLO, a combination of two Flow Control Valves (FCVs) must be used, but you have layout and placement options. The example below will demonstrate them. 

 Figure 1 shows a section of piping where a 3-way control valve will be used.

 

The total flow into the section is 400 cfm and we want the flow to split 75% / 25% between the AHU branch and the bypass branch. There are two options for accomplishing this. 

The first option is shown in Figure 2.

The flow rate is set in each branch (75% of the total flow through the AHU branch and 25% of the total flow through the bypass branch). Note that the total flow into the section will be equal to the sum of the set FCVs (300 cfm + 100 cfm = 400 cfm). 

 

The second option is shown in Figure 3.


The total flow rate into the section is set with an FCV set to 400 cfm.  The flow is then split between the AHU and bypass branches by specifying the flow rate with an FCV in one of the branches (in this example, 300 cfm in the AHU branch).  The flow rate through the bypass line will then be equal to 100 cfm (400 cfm – 300 cfm = 100 cfm).

NOTE:  If the results calculated for the FCV in the AHU branch turn out to be "Invalid," i.e. there is pressure gain across the valve instead of an pressure drop, then you should remove the FCV from that branch and instead install the FCV in the bypass branch at 100 cfm. See Knowledge Base, "Finding the Most Hydraulically Remote Loop."

 

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