Pump Operating Pressure

Atlantic Feedwater Systems specializes in economical boiler feedwater systems that use Simplex, Duplex, and Triplex centrifugal pumps

Simplex systems use one pump, Duplex use two pumps for one boiler feedwater system, and Triplex systems have two boilers with three pumps (one pump is standby). Centrifugal pumps make customary boiler feed pump oversizing unnecessary due to their extremely low wear characteristics.

Standard Centrifugal Pumps:

• Higher efficiency than turbine type pumps.
• Less maintenance.
• Less wear and tear on the centrifugal pumps than on turbine type pumps.
• Single stage for low-pressure steam systems.
• Multistage for high-pressure steam systems.

The Boiler Feed Pumps are available in standard sizes for easy selection. The feed pumps are cataloged for specific discharge pressures. The discharge pressure listed in the literature is the operating pressure of the boiler. The pump chosen includes additional head to overcome the pipe losses between the feed pump and the boiler. All sizing assumes “On-Off” feedwater control.

If you would like to size the pump, or the discharge pressure is different than the catalog sizing, calculate the discharge pressure this way:

1. Add for pressure drop in the piping

If On-Off pump control is used, add for the pipe loss between the boiler and pump, as well as for the drop across the feedwater stop and check valves. Common practice allows about 20 psig for these pressure drops.

If Modulating Feedwater Control is used, an additional pressure drop is required by the feedwater valve. Most feedwater valves are sized in the range to produce between 10 psig and 30 psig pressure drop at full flow. Most people use 25 or 30 psig pressure across the valve for sizing purposes. This is in addtion to the piping valve losses.

2. Convert the discharge pressure to Total Dynamic Head in feet (TDH)

Pump discharge pressure is rated in feet of head. To convert from psig to feet of head, multiply the calculated pressure by 2.31 to get Total Dynamic Head in feet (TDH).

If the water is near the boilng point, you may wish to correct for the specific gravity of the water. At 212º F water divide the TDH by 0.96 to get the head to use to find the pump discharge pressure