Sizing of Series 125 Valves - Booster Pump Control

1. Decide whether a globe or angle valve will best fit your installation. Keep in mind that it is always best to install any control valve “bonnet up,” particularly in sizes 8” and larger.
   
2. Begin with a line sized valve, i.e, the same size as the pump discharge.
   
   Calculate the pressure drop from the formula,
   
   where:
   • DP = pressure drop, psi
   • sg = specific gravity of line fluid (water = 1.0)
   • Q = rated flow of pump, gpm
   • Cv = Valve coefficient from Table 2.
   
   
3. The pressure drop calculated is that for a wide-open apply and would be true for the dual-chambered 125-27 valve regardless of flow rate. On the other hand, the single-chambered valve may not be wide open. Refer to the “wide open at” column of Table 2. If the flow rate is less than this figure, the pressure drop of the single-chambered valve can be 2-3 psi higher than the value calculated in Step 2. If the flow rate is higher than the figure given, the single-chambered valve will be wide open and will have a pressure drop equal to the dual-chambered valve.
   
4. Check to see that the flow velocity does not exceed 20 ft/sec. If it does, or if the pressure drop is excessive, consider using the next size larger valve.
   
5. Finally, if the 125-27 valve is selected, make note of the diaphragm chamber discharge. This quantity of water will be discharged to atmosphere each time the valve opens or closes. Provision should be made to drain or otherwise dispose of this water.

Sizing of Series 126 Valves - Deep Well Pump Control

1. Decide whether a globe or angle valve will best fit your installation. Keep in mind that it is always best to install any control valve “bonnet up,” particularly in sizes 8” and larger.
   
2. Carefully examine your pump curve. Make note of the flow rate at which the pump discharge pressure is reduced to a point just below system static pressure.
   
   Calculate the required valve CV from the formula:
   
   where:
   • Q = flow rate as determined in Step 2, gpm
   • PS = system static pressure, psi
   • sg = specific gravity of line fluid (water = 1.0)
   
   
   
   
3. Using either the globe or angle valve column of Table 2, pick the smallest size valve that has a CV at least equal to that calculated in Step 3.
   
4. Using the flow rate determined in Step 2, make sure the velocity does not exceed 30 ft/sec.
   
5. Finally, make note of the diaphragm chamber discharge. This quantity of water will be discharged to atmosphere each time the valve opens or closes. Provision should be made to drain or otherwise dispose of this water.