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Sizing Balancing Orifices

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In the system below, the flow rate required in each distribution line is 300 gpm. In order to reduce the system cost and complexity, the same control valve is installed in all three distribution lines. For the design flow rate, the particular valve we will be using has a controlling range of 5 to 25 psi. Balancing orifices may be needed in one or more of the lines if the pressure drop required across the valve is outside of the specified operating range.

We can calculate the system and note the pressure drops across the control valves.

Distribution Line	FCV	dP (psi)
1	CV-1	45.43
2	CV-2	29.33
3	CV-3	20.03

Note that the pressure drops in distribution lines 1 and 2 are outside of the control valve operating range of 5 to 25 psi. For these two lines, balancing orifices will be installed to provide an additional fixed pressure drop. This will reduce the pressure drops required across the control valves.

Each orifice will be sized so that the maximum pressure drop across the control valve will be 20 psi:

Distribution Line	Orifice dP (psi)
1	(45.43 - 20) = 25.43
2	(29.33 - 20) = 9.33

Below is the dialog box for sizing an orifice.

Now let's look at the system with the balancing orifices installed.

Notice that with the balancing orifices, the pressure drops across CV-1 and CV-2 are approximately 20 psi.