Extraction Steam Check Valve
check · pressure seal bonnet
- Body
- A105, A182 F11, F22
- Size
- NPS 6-48 (DN 150-1200)
- Class
- Class 150-900
- Temp
- 150-450 °C by extraction stage
- Standard
- ASME B16.34
Steam Turbine
Around the machine, the governing requirement is protection: stopping reverse steam, draining condensate before it reaches the blades, and isolating reliably for outages.
Typical conditions
| Parameter | Value | Basis |
|---|---|---|
| Inlet conditions | Main steam conditions at the stop valve | per project |
| Extraction stages | 3-8 typical on a utility machine | typical |
| Extraction pressure | 0.05-5 MPa depending on stage | typical |
| Protection response | Sub-second on large HP extractions | per project |
Extraction non-return is a protection function
On a trip, the inventory in each feedwater heater flashes and drives steam back toward the turbine. Reverse steam through the extraction nozzles can overspeed the rotor. The extraction check valve exists for that event alone, and its selection follows the turbine protection study - line volume, heater inventory, and the machine manufacturer requirements.
- Power-assisted closure on large HP and IP extractions
- Limit switches so the protection system knows the valve actually closed
- Partial-stroke test provision where the valve must be proven online
Turbine drains protect the blading
Condensate entering the steam path damages blades. Drain valves have to open reliably on startup, close tightly in normal running, and survive flashing flow in between. Hardfaced globe construction, and a defined exercise routine so a valve that sits idle for months still works when needed.
Gland steam and leak-off
Modest conditions, but the valves are numerous, often inaccessible, and rarely given attention in the specification. Standard forged construction; the thing worth specifying carefully is the operator and the accessibility.
What we need from you
The turbine protection requirements if you have them, the extraction line geometry, and the heater data. Without these, an extraction check valve is being selected on size and class alone - which is how a protection device ends up not protecting anything.
Materials commonly used here
Indicative only. The grade is set by the piping class and the ASME B16.34 rating at your design temperature - see the material matrix.
Recommended products
Pressure Seal Globe Valve
globe · pressure seal bonnet
- Body
- A105, A182 F11, F22, F91, F92
- Size
- NPS 2-16 (DN 50-400)
- Class
- Class 900 - 4500
- Temp
- up to 650 °C / 1200 °F
- End
- BW, SW, RTJ, RF
- Standard
- ASME B16.34
Main Steam Valve
Gate / globe / check · pressure seal bonnet
- Body
- A182 F22, F91, F92
- Size
- NPS 2-24 (DN 50-600)
- Class
- Class 1500 - 4500
- Temp
- 540 - 650 °C for USC main steam
- End
- BW
- Standard
- ASME B16.34
Stop-Check Valve
stop check · pressure seal bonnet
- Body
- A182 F22, F91, F92
- Size
- NPS 2-16 (DN 50-400)
- Class
- Class 900 - 2500
- Temp
- up to 620 °C / 1148 °F
- End
- BW, RTJ, RF
- Standard
- ASME B16.34
Frequently asked questions
Does the turbine OEM have to approve the extraction check valves?
On most projects, yes, or at least the protection scheme has to be consistent with their requirements. Send us their specification with the enquiry rather than after the order - it frequently changes the valve arrangement, not just the documentation.
Can extraction valves be tested with the unit running?
Partial-stroke, yes, if the provision is designed in. Full closure testing needs an outage. Ask for the provision at the enquiry stage; adding it later usually means a new valve.
Further reading
Discuss this application
Send the system conditions and we will come back with what we would supply, the rating basis, and any point where we would question the specification.