Feedwater Valve
Isolation and non-return on the feedwater circuit - the highest-pressure water service in the plant, with cavitation and flashing as the dominant wear mechanisms.
- Size NPS 2-20 (DN 50-500)
- Pressure class Class 1500, 2500
- Design temperature 150-300 °C typical
- Body material A105N, A182 F11, F22; WB36 where specified
- End connection BW to ASME B16.25, flanged RF or RTJ
Overview
Feedwater service runs at the highest pressure in the plant - the pump has to overcome drum pressure plus static head plus losses - but at moderate temperature. The failure mechanisms are different from steam: cavitation and flashing damage rather than creep. Valve selection focuses on avoiding partial-open operation and getting the check valve dynamics right on parallel pumps.
Target systems
- Boiler feed pump discharge and suction isolation
- Feedwater heater inlet, outlet and bypass
- Economiser inlet
- Pump minimum-flow recirculation
- Feedwater startup and control station isolation
- Minimum-flow recirculation control. That duty needs a purpose-built recirculation valve with staged pressure letdown - a gate valve throttled at 5 % will destroy itself.
- Service where the NPSH margin has not been checked. A valve cannot fix a cavitating pump, and cavitation damage in the valve body will be misattributed to the valve.
- Two-phase flow across the seat without a flashing-service trim assessment.
Technical data
Every value is marked standard for the catalogue range, typical where it depends on material or configuration, or per project where it can only be confirmed against your specification.
| Parameter | Value | Basis |
|---|---|---|
| Size | NPS 2-20 (DN 50-500) | standard |
| Pressure class | Class 1500, 2500 Feedwater pressure is often higher than main steam pressure - check the pump curve, not the drum. | standard |
| Design temperature | 150-300 °C typical | typical |
| Medium | Deaerated feedwater, condensate | standard |
| Body material | A105N, A182 F11, F22; WB36 where specified | standard |
| Valve type | Pressure seal gate for isolation, swing or piston lift check for non-return | standard |
| Trim | 13Cr / F6a, Stellite 6 hardfaced | standard |
| End connection | BW to ASME B16.25, flanged RF or RTJ | standard |
| Operation | Handwheel, bevel gear, electric actuator | standard |
| Cavitation assessment | On request, against your duty point | per project |
Design
WB36 where the specification calls for it
WB36 (15NiCuMoNb5) is common in European-designed feedwater systems for its strength at moderate temperature. It is not interchangeable with A105 or F22 and has its own welding and heat treatment requirements. If your specification names it, we treat it as a hard requirement rather than proposing a substitute.
Check valve dynamics on parallel pumps
The critical case is one pump tripping while the others run. A swing check that closes too slowly lets reverse flow spin the tripped pump backwards. We supply disc mass and geometry data so your surge analysis can confirm the closure time, and will recommend a piston lift or a damped design where the numbers call for it.
Hardfaced seating against cavitation damage
Stellite 6 overlay resists the impingement damage that follows any flashing across the seat. It slows the damage; it does not make the valve immune. The real fix is not throttling with an isolation valve, and we say so.
Full-bore gate for minimum loss
On the pump discharge, pressure drop across the isolation valve is parasitic pumping power for the life of the plant. Full-bore gate construction with a matched bore to the pipe keeps that loss to the minimum available.
Standard material specifications
Part numbering follows the general arrangement drawing. Three columns cover the common temperature bands; the actual configuration for your order is confirmed on the datasheet.
| No. | Part name | Carbon steel | Low alloy | Creep grade |
|---|---|---|---|---|
| 1 | Body | A105 / A105N | A182 F11, F22 | A182 F91, F92 |
| 2 | Seat ring | 13Cr + Stellite 6 | 13Cr + Stellite 6 | F91 + Stellite 6 |
| 3 | Wedge (flexible) | A105 + Stellite 6 | F11 / F22 + Stellite 6 | F91 + Stellite 6 |
| 4 | Stem | A182 F6a | A182 F6a Cl.2 | A182 F6NM / 422SS |
| 5 | Bonnet | A105 / A105N | A182 F11, F22 | A182 F91, F92 |
| 6 | Pressure seal ring | Flexible graphite + SS liner | Flexible graphite + SS liner | Flexible graphite + Inconel liner |
| 7 | Thrust ring (segmental) | A105 | A182 F11 / F22 | A182 F91 |
| 8 | Retainer segments | A105 | A182 F11 / F22 | A182 F91 |
| 9 | Gland | A105 | A182 F11 / F22 | A182 F91 |
| 10 | Gland flange | A105 | A105 | A182 F91 |
| 11 | Stem packing | Flexible graphite | Flexible graphite | Flexible graphite, low-leakage set |
| 12 | Gland eyebolt / pin | A193 B7 / A194 2H | A193 B16 | A193 B16 |
| 13 | Yoke | A105 / WCB | A105 / WCB | A105 / WCB |
| 14 | Yoke bushing | Ni-Al bronze | Ni-Al bronze | Ni-Al bronze |
| 15 | Back seat | 13Cr overlay | 13Cr overlay | Stellite overlay |
| 16 | Handwheel | Ductile iron / carbon steel | Ductile iron / carbon steel | Ductile iron / carbon steel |
| 17 | Nameplate | AISI 304 | AISI 304 | AISI 304 |
Standards
What each standard actually governs on this valve. A standard listed without a scope is decoration.
| Standard | Applies to |
|---|---|
| ASME B16.34 | Pressure-temperature ratings, materials, wall thickness, testing and marking. This is the base rating standard for the valve - it is what fixes the allowable pressure at your design temperature. |
| ASME B16.10 | Face-to-face and end-to-end dimensions. Relevant when the valve replaces an existing one or has to drop into a fixed spool. |
| ASME B16.25 | Butt welding end preparation, including bore and bevel geometry for the matching pipe schedule. |
| ASME B16.5 | Flanged end dimensions and ratings, when the valve is supplied with RF or RTJ flanges rather than weld ends. |
| API 598 | Inspection and pressure testing - which tests are mandatory, test durations and allowable leakage. We state the shell and seat test scheme on the ITP. |
| MSS SP-61 | Alternative pressure testing scheme for steel valves, used where the project specification calls for it instead of API 598. |
| MSS SP-25 | Marking of the body and the nameplate - size, class, material heat, figure number and flow direction where applicable. |
Dimensions
Face-to-face per ASME B16.10 where tabulated. Weights are indicative and vary with class, material and operator - confirm against the approved GA drawing.
| Size | DN | Face-to-face | Weight (typical) |
|---|---|---|---|
| NPS 2 | DN 50 | 368 mm | ~55 kg |
| NPS 3 | DN 80 | 470 mm | ~105 kg |
| NPS 4 | DN 100 | 546 mm | ~180 kg |
| NPS 6 | DN 150 | 705 mm | ~390 kg |
| NPS 8 | DN 200 | 832 mm | ~700 kg |
| NPS 10 | DN 250 | 991 mm | ~1150 kg |
| NPS 12 | DN 300 | 1130 mm | ~1750 kg |
| NPS 16 | DN 400 | 1410 mm | ~3200 kg |
Inspection
- Hydrostatic shell test to API 598 / MSS SP-61
- Hydrostatic or pneumatic seat test, leakage rate per specification
- Back seat test (gate and globe, where a back seat is supplied)
- PMI on all pressure-containing parts and welded overlays
- NDE per specification - RT, UT, MT or PT as applicable
- Hardness survey after post-weld heat treatment
- Dimensional inspection against approved GA drawing
- Material certification EN 10204 3.1 (3.2 on request)
- Visual and functional check, full stroke on the manual operator
The actual scope, and which points are hold or witness, is set on the Inspection and Test Plan agreed before manufacture.
Documents supplied
- Product datasheet
- General arrangement (GA) drawing
- Inspection & Test Plan (ITP)
- Material test certificate (MTC) EN 10204 3.1
- Hydrostatic and seat test report
- PMI report
- NDE reports as applicable
- Heat treatment charts
- Dimensional report
- Packing list and preservation record
What each document proves, and which ones suppliers most often cannot produce
Manufacturing evidence
These positions are reserved for photographs of actual DERVOS VALVE production. They are shown as placeholders rather than filled with stock or rendered images - see the note on the company page about what this site will and will not claim.
Frequently asked questions
Why is my feedwater valve a higher class than my main steam valve?
Because the feed pump has to develop more pressure than the drum runs at. Feedwater at Class 2500 alongside main steam at Class 1500 is normal, not an error in the piping class. Size the valve from the pump discharge condition.
Can I use a gate valve for minimum-flow recirculation?
No. Recirculation runs continuously at high differential pressure with flashing across the restriction. That needs a multi-stage recirculation valve. Using an isolation gate valve there will destroy the seat within months and is one of the more common specification mistakes we see.
What material for feedwater at 250 °C?
A105N or F11 covers most of it; F22 where the specification wants extra margin; WB36 where the design is European in origin. Temperature is not the constraint here - pressure class and the client specification usually are.