Size Vacuum Boiler Feed
Pump Flow Rate
Each pump on a boiler feed unit is sized based on the total load of boilers fed by the specific pump feeds at one time. For boiler feed pumps running ON/OFF, the pumps are controlled by a boiler level controller.
Boiler Feed Pump Receiver Size
The receiver size on boiler feed units is typically based on the total system load of all boilers fed by the boiler feed unit with 20 minutes GROSS storage. The size of boiler feed receivers are expressed in gross gallons. Make sure the inlet height is lower or equal to exisiting height on gravity return systems—water does not run uphill!3
Vacuum Air Producer Sizing
Vacuum Air Producer Size is determined from TOTAL system load given for Boiler Feed Pump Receiver Size. If system is new, load is calculated based on 0.5 cubic feet of air removed per minute (CFM) for each 1000 square feet EDR. If an older system, load is based on 0.7 CFM per 1000 sq. ft. EDR to compensate for leaks. 4
Pump Discharge Pressure
Assumes proper discharge pipe size of a velocity of 10 ft/sec or less. Pump discharge pressure MUST BE ABLE to overcome the boiler safety relief valve setting plus 3% of valve setting AND meet all state and local codes. Discharge pressure of pumps based on the larger amount. This amount is either the Safety Relief Valve setting on boiler + 3% OR Boiler Operating Pressure + Valve Pressure Drops + Safety Margin.
If boiler and boiler feed unit are on the same floor, enter a value of "0" (zero) for feet of head. If boiler is located on a floor above the boiler feed unit, enter vertical height (in feet) from the pump discharge of the boiler feed pump up to the inlet piping on the boiler.
If the pressure differential between the boiler operating pressure and the setting of the safety relief valve on the boiler is greater than 20 psig, consider replacing the safety valve with one rated closer to the boiler operating pressure. Otherwise the motor horsepower of the boiler feed pumps will need to be oversized to provide a discharge pressure sufficient to overcome the rating of the safety relief valve on the boiler. The higher motor HP typically would require a more expensive pump and increases ongoing operating costs.
- Each pump on a boiler feed unit is sized based on the total load of boilers fed by the specific pump feeds at one time.
- For boiler feed pumps running ON/OFF, the pumps are controlled by a boiler level controller.
- The receiver size on boiler feed units is typically based on the total system load of all boilers fed by the boiler feed unit with 20 minutes GROSS storage. The size of boiler feed receivers are expressed in gross gallons. Make sure the inlet height is lower or equal to exisiting height on gravity return systems—water does not run uphill!
- If new system, load is calculated based on .5 cubic feet of air removed per minute (CFM) for each 1000 square feet EDR. If older system, based on .7 CFM per 1000 sq. ft. EDR to compensate for leaks in the system.
- If boiler and boiler feed unit are on the same floor, enter a value of "0" for feet of head. If boiler is located on a floor above the boiler feed unit, enter vertical height (in feet) from the pump discharge of the boiler feed pump up to the inlet piping on the boiler.
- Assumes pressure drop through modulating valve of 10 psig or less.
- Assumes pressure drop through stack economizer of 20 psig or less.
- Assumes proper discharge pipe size of a velocity of 10 ft/sec or less.
- Pump discharge pressure MUST BE ABLE to overcome the boiler safety relief valve setting plus three percent of valve setting AND meet all state and local codes.
- If the pressure differential between the boiler operating pressure and the setting of the safety relief valve on the boiler is greater than 20 psig, consider replacing the safety valve with one rated closer to the boiler operating pressure. Otherwise the motor horsepower of the boiler feed pumps will need to be oversized to provide a discharge pressure sufficient to overcome the rating of the safety relief valve on the boiler. The higher motor HP typically would require a more expensive pump and increases ongoing operating costs.
- Pump flow rate is < 0.5 gallons/min (gpm). Contacting your Shipco® representative is advised.
- Pump flow rate is > 500 gallons/min (gpm). Contacting your Shipco® representative is advised.