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
Boiler & Steam Systems
The small valves around a boiler are specified last and cause the most trouble. Wet steam, flashing and frequent operation are the common thread.
Typical conditions
| Parameter | Value | Basis |
|---|---|---|
| Drum pressure | 4-20 MPa depending on unit type | typical |
| Drain and vent service | Saturated and wet steam, flashing across the seat | standard |
| Blowdown | High solids content, severe flashing | standard |
| Operating frequency | Daily to continuous on some drains | per project |
Drains and vents: throttling-tolerant seating required
A boiler drain is opened against full drum pressure into atmosphere or a flash tank. The flow flashes across the seat and carries whatever is in the water with it. Hardfaced globe valves handle this; anything with a soft seat or a plain 13Cr seat will not last a season.
- Globe construction with a plug-type disc and Stellite 6 overlay
- Under-the-seat flow so the packing is unpressurised when closed
- Two valves in series on high-pressure drains, one for isolation and one for throttling
Blowdown: solids plus flashing
Continuous blowdown carries dissolved solids; intermittent bottom blowdown carries sludge. Both flash across the restriction. The correct arrangement is an isolation valve upstream that stays fully open or fully closed, and a purpose-designed blowdown valve doing the letting-down.
Startup vents and warm-up lines
These operate hard for a short period on every start and then sit idle. The failure mode is not wear but seizure - a valve that has not moved for weeks being asked to operate reliably during startup. Back seats, correct packing and a defined exercise routine matter more than seat hardness here.
Soot blower and auxiliary steam isolation
Moderate conditions, high cycle count, and often overlooked in the specification. Standard forged construction covers it; the thing to get right is the operator, because these valves are frequently remote and infrequently accessible.
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
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
Pressure Seal Gate Valve
gate · pressure seal bonnet
- Body
- A105, A182 F11, F22, F91, F92
- Size
- NPS 2-24 (DN 50-600)
- Class
- Class 600 - 4500
- Temp
- up to 650 °C / 1200 °F
- End
- BW, SW, RTJ, RF
- Standard
- ASME B16.34
Frequently asked questions
Why two valves in series on a high-pressure drain?
So one valve does the throttling and takes the wear, while the other stays fully open or fully closed and provides reliable isolation. Trying to do both jobs with one valve means the isolation valve is also the eroded one, which is exactly the valve you do not want to depend on.
Can a gate valve be used on a drain line?
As the upstream isolation valve, yes, provided it is operated fully open or fully closed. As the throttling valve, no - a partly open wedge in flashing flow erodes quickly and unevenly.
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.