Boiler feedwater pumps · deaerator-to-boiler duty above boiler pressure, motor or steam-turbine drive, continuous running in modulating systems, NPSH available versus required, minimum flow and internal recirculation, fluid power and efficiency
A feedwater (boiler feed) pump takes treated, deaerated water and pumps it into a boiler or steam generator against boiler pressure; because the water is hot and close to saturation, suction conditions matter as much as discharge head. Ask three things first: what flow and discharge pressure the boiler needs across its load range, what net positive suction head the deaerator and suction piping provide, and how the pump is driven and protected at low flow.
Feedwater pumps for industrial and utility steam boilers and steam generators: horizontal and vertical multistage centrifugal pumps and reciprocating (plunger) feed pumps, motor- or turbine-driven. Condensate pumps, circulating pumps, deaerators and boilers themselves (separate product pages) are outside this page except where compared.
01
The US Department of Energy's steam system sourcebook describes the cycle: condensate and makeup water go to the deaerator, which strips oxygen and non-condensable gases, and the boiler feed pumps raise the feedwater pressure above boiler pressure and inject it into the boiler. Feedwater pumps transfer water from the deaerator to the boiler, are driven by electric motors or steam turbines, and in a modulating feedwater system run constantly, rather than cycling on and off as in relatively small boilers; a modulating feedwater flow control valve responds to the water level transmitters. [1]
DOE's pumping sourcebook gives fluid power as head × flow × specific gravity / 3,960 (in horsepower, with head in feet and flow in US gpm); the motor power needed is higher because of pump and motor inefficiencies. [2]
Editorial calculation: a feed pump delivering 100 gpm against 500 ft of head with water of specific gravity 0.96 needs 100 × 500 × 0.96 / 3,960 ≈ 12.1 hp of fluid power; at 60% pump efficiency that is about 20.2 hp at the shaft. Flow, head, specific gravity and efficiency are assumed examples; derive head from boiler pressure plus valve, economiser and piping losses at maximum steam load.
For steam plant on US-flag vessels, the Coast Guard's marine engineering rules set redundancy and pressure ratings around the feed pump (46 CFR 56.50-30 and 56.50-10). Steam vessels, and motor vessels with steam-driven generators, need at least two separate means of supplying boiler feedwater. In a group feed system, a vessel with a feed pump attached to the main propulsion unit also needs one independently driven feed pump able to supply the operating boilers at normal capacity plus a second independent pump rated at 75% of normal capacity; two independent pumps each rated at full normal capacity, used only for feed, remove the need for a third. In a unit feed system each boiler has its own independently driven main feed pump plus an auxiliary pump of the same capacity, one auxiliary serving no more than two boilers, with pump discharge controlled automatically by boiler water level and manual control as well. Feed discharge piping up to the stop valves is designed for the feed pump relief valve setting or, with no relief valve, the pump's shutoff head; piping from the boiler through the stop and stop-check valves must exceed the boiler's maximum allowable working pressure by 25% or 225 psig, whichever is less. Feed pumps for water-tube boilers may have freshwater connections only, and each boiler feed pump needs a discharge pressure gauge. [4]
Editorial calculation: for a boiler with a 600 psig maximum allowable working pressure, 25% more is 750 psig and 600 + 225 is 825 psig, so the boiler-side feed piping design pressure must exceed 750 psig; at 1,000 psig the figures are 1,250 and 1,225 psig, so 1,225 psig governs. The pump's shutoff head therefore matters for the discharge piping rating, so ask the supplier for shutoff head and relief valve setting with the curve. [4]
Give the supplier the boiler type and maximum working pressure, required flow at minimum, normal and maximum load, discharge head including control valve and economiser losses, feedwater temperature and quality, deaerator pressure and height (NPSH available), drive (motor, steam turbine, variable speed), control method (modulating or on/off), minimum-flow recirculation arrangement, pump type (multistage centrifugal or reciprocating), materials and seals, standards, and number of pumps (duty/standby).
02
DOE's pumping sourcebook explains that NPSH available (NPSHA) is a function of the system and flow, while NPSH required (NPSHR) is a function of the pump and flow and appears on pump curves. The Hydraulic Institute determines NPSHR, now termed NPSH3, where the pump's total head, or the first-stage head of a multistage pump, drops by 3% because of cavitation; pumps need a much higher margin away from the best efficiency point, and DOE's sourcebook says "a common rule in system design is to ensure that NPSHA is 25% higher than NPSHR for all expected flow rates". Internal recirculation at low flow forms damaging vortices, so manufacturers list minimum flow rates that operators should respect. [2]
Editorial calculation: if the pump curve shows NPSHR of 10 ft at the highest expected flow, the suction system should provide at least 1.25 × 10 = 12.5 ft of NPSHA there. The NPSHR value is an assumed example; check the margin at every flow the pump will see, including run-out.
03
Suppliers linked to this page list boiler feed pumps; each card links to the page reviewed.
Listings include DG-type multistage boiler feed pumps alongside other centrifugal and vacuum pumps, and reciprocating boiler feed pumps among plunger and high-pressure pumps. Ask each for the pump curve with NPSHR, minimum flow, materials and drive options.
04
Grundfos's installation and operating instructions for its CR, CRI and CRN vertical multistage centrifugal pumps give the inlet check a feed pump buyer can ask any supplier to reproduce: H = pb × 10.2 − NPSH − Hf − Hv − Hs, where pb is barometric pressure in bar (system pressure in closed systems), NPSH is read at the highest flow the pump will deliver, Hf is inlet pipe friction loss, Hv is vapour pressure at the liquid temperature, and Hs is a safety margin of at least 0.5 metres head. A negative H means an inlet pressure of at least H metres head is required. Grundfos's worked example for a CR 15 at 15 m³/h and +60 °C gives H = 1 × 10.2 − 1.1 − 3.0 − 2.1 − 0.5 = 3.5 metres head. [3]
The same manual states that CR, CRI and CRN pumps are not suitable for liquids above 120 °C for long periods, and that pumping above +120 °C may cause periodical noise and reduced pump life; the shaft seals with EPDM (HQQE, HBQE) are rated to 120 °C. It warns against running below the minimum flow rate, given as a percentage of rated flow that depends on liquid temperature, because of the risk of overheating, and says the pump must not run against a closed outlet valve. [3]
Starts per hour are limited by motor size, from 250 for motors up to 2.2 kW to 50 for 5.5–11 kW and 40 for 18.5–22 kW, which matters for on/off level control. The pumps are pressure-tested at 1.5 times the stated maximum pressure. Ask the supplier for the minimum-flow curve, NPSH curve and start limit of the model offered at your feedwater temperature. [3]
05
This is a functional reference built from the sources cited; it is not one maker's specification.
| Element | Role | Fix in the order |
|---|---|---|
| Deaerator | Removes oxygen; feeds pump suction. [1] | Pressure and elevation. |
| Feed pump | Raises pressure above boiler pressure. [1] | Type, stages, curve. |
| Drive | Electric motor or steam turbine. [1] | Drive and speed control. |
| Feedwater control valve | Modulates with boiler water level. [1] | Valve and pressure drop. |
| Minimum-flow protection | Avoids internal recirculation damage. [2] | Minimum flow and bypass. |
06
A feed pump quotation needs values for your boiler. The table explains each field, gives published values where a reviewed source states them, and says what to obtain from the supplier.
| Field | What it means and published values | Ask the supplier for |
|---|---|---|
| Discharge pressure | Above boiler pressure. [1] | Head at each flow. |
| Flow range | Modulating systems run constantly. [1] | Minimum, normal, maximum. |
| NPSH | NPSH3 at 3% head drop; NPSHA ≥ 1.25 × NPSHR rule. [2] | NPSHR curve. |
| Minimum flow | Maker-listed to avoid recirculation. [2] | Value and bypass design. |
| Power | Fluid power = HQ·s.g./3,960 hp. [2] | Efficiency and motor size. |
| Drive | Motor or steam turbine. [1] | Drive type. |
07
Paste it into your enquiry below or into an email to a maker, then replace every bracket.
Boiler: [type; pressure; steam load range] Duty: [flow min/normal/max; head] Suction: [deaerator pressure; elevation; NPSHA] Water: [temperature; treatment] Drive: [motor/turbine; VFD] Protection: [minimum flow; bypass] Scope: [pumps; duty/standby; materials; seals]
These companies list boiler feed pumps.
Lists DG-type boiler feed pumps with centrifugal and vacuum pumps.
Product scope checked 2026-10-11
Lists boiler feed pumps among reciprocating and high-pressure pumps.
Product scope checked 2026-10-11
Explore company information and manufacturing capabilities, then discuss the scope of your project with a relevant supplier.
DOE describes it as raising feedwater pressure above boiler pressure and transferring water from the deaerator into the boiler. [1]
DOE says "a common rule in system design is to ensure that NPSHA is 25% higher than NPSHR for all expected flow rates". [2]
At low flow, internal recirculation forms damaging vortices; makers list minimum flows to avoid it. [2]
Grundfos's CR, CRI, CRN instructions use a safety margin of at least 0.5 metres head in its minimum inlet pressure calculation, with NPSH read at the highest flow the pump will deliver. [3]
46 CFR 56.50-30 requires at least two separate means of supplying feedwater; in a unit feed system each boiler has its own main feed pump plus an auxiliary pump of the same capacity. [4]
Sources checked 2026-10-11. Both sources are US Department of Energy sourcebooks for industry (cited from Internet Archive copies of energy.gov files); the pumping sourcebook was developed with the Hydraulic Institute. The US Coast Guard's 46 CFR 56.50-30 sets feed pump redundancy and feed piping pressure for vessels.
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