Dervos valve · Product specification
Pressure Seal Globe Valve
Self-energizing bonnet globe valve for tight shut-off and controlled throttling in high-pressure steam, drain and vent service.
- Size
- NPS 2-16 (DN 50-400)
- Pressure class
- Class 900 - 4500
- Body material
- A105, A182 F11, F22, F91, F92
- End connection
- BW to ASME B16.25, SW, flanged RF or RTJ
- Operation
- Handwheel, bevel gear, electric or pneumatic actuator
Catalogue ranges for initial selection. Final rating and configuration are confirmed against your project specification.
Have an MTO or datasheet? Send it with size, class, material, quantity and required delivery.
01 / Selection data
Technical specifications
Use these ranges to shortlist the valve. Values marked “confirm per order” depend on the selected size, material or project standard.
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| Parameter | Specification | Basis |
|---|---|---|
| Size | NPS 2-16 (DN 50-400)Above NPS 16 a globe valve is rarely the right choice; confirm the application first. | Catalogue range |
| Pressure class | Class 900 - 4500 | Catalogue range |
| Design temperature | up to 650 °C / 1200 °FSet by body material and the B16.34 rating table. | Configuration dependent |
| Medium | Superheated steam, saturated steam, condensate, feedwater | Catalogue range |
| Body material | A105, A182 F11, F22, F91, F92 | Catalogue range |
| Disc type | Plug type, standard; ball or needle type on request | Catalogue range |
| Trim material | 13Cr / F6a, hardfaced with Stellite 6 | Catalogue range |
| Flow direction | Under the seat, marked on the bodyOver-the-seat is available where the specification requires it - state this at enquiry. | Catalogue range |
| End connection | BW to ASME B16.25, SW, flanged RF or RTJ | Catalogue range |
| Operation | Handwheel, bevel gear, electric or pneumatic actuator | Catalogue range |
| Face-to-face | ASME B16.10 | Catalogue range |
| Leakage class | Per API 598 or project specification | Confirm per order |
02 / Engineering
Valve design & materials
Plug-type disc and hardfaced seat
The disc has an extended plug profile that enters the seat bore before contact, so the last part of the stroke is guided. Both surfaces carry Stellite 6 overlay. This is what allows limited throttling without wire-drawing the seat, though sustained throttling at small openings is still a control valve duty.
Under-the-seat flow
Standard flow direction puts line pressure under the closed disc, which leaves the bonnet cavity and packing at low pressure when the valve is shut. It also means the stem must be pushed closed against pressure - a factor when sizing an actuator.
Pressure seal bonnet
Same self-energizing arrangement as the gate valve: bonnet inserted from inside, tapered graphite ring, segmental retainer. No bolted joint to relax during thermal cycling.
Swivelling disc-to-stem connection
The disc is retained on the stem so it can rotate slightly and align itself to the seat. It does not turn with the stem, so the seating faces are not scrubbed on every close.
Forged body with machined internal web
The internal partition that creates the S-shaped flow path is machined into the forging rather than formed by a core, which removes a common location for casting defects in this valve type.
Reference material configurations
Material combinations are examples for selection; the final bill of materials is agreed for each order.
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| Part | Carbon steel | Alloy steel | F91 / F92 |
|---|---|---|---|
| Body | A105 / A105N | A182 F11, F22 | A182 F91, F92 |
| Seat ring | 13Cr + Stellite 6 | 13Cr + Stellite 6 | F91 + Stellite 6 |
| Disc (plug type) | A105 + Stellite 6 | F11 / F22 + Stellite 6 | F91 + Stellite 6 |
| Disc nut / stem coupling | A182 F6a | A182 F6a | A182 F6NM |
| Stem | A182 F6a | A182 F6a Cl.2 | A182 F6NM / 422SS |
| Bonnet | A105 / A105N | A182 F11, F22 | A182 F91, F92 |
| Pressure seal ring | Flexible graphite + SS liner | Flexible graphite + SS liner | Flexible graphite + Inconel liner |
| Thrust ring (segmental) | A105 | A182 F11 / F22 | A182 F91 |
| Retainer segments | A105 | A182 F11 / F22 | A182 F91 |
| Gland | A105 | A182 F11 / F22 | A182 F91 |
| Stem packing | Flexible graphite | Flexible graphite | Flexible graphite, low-leakage set |
| Yoke / yoke bushing | WCB / Ni-Al bronze | WCB / Ni-Al bronze | WCB / Ni-Al bronze |
| Back seat | 13Cr overlay | 13Cr overlay | Stellite overlay |
| Handwheel | Ductile iron / carbon steel | Ductile iron / carbon steel | Ductile iron / carbon steel |
| Nameplate | AISI 304 | AISI 304 | AISI 304 |
03 / Reference dimensions
Dimensions & approximate weight
Typical reference values only. Request the approved GA drawing and confirmed weight for your selected class and configuration.
Swipe or scroll sideways to view the full table.
| NPS | DN | Face to face / end to end | Approx. weight |
|---|---|---|---|
| NPS 2 | DN 50 | 368 mm | ~60 kg |
| NPS 3 | DN 80 | 470 mm | ~115 kg |
| NPS 4 | DN 100 | 546 mm | ~195 kg |
| NPS 6 | DN 150 | 705 mm | ~420 kg |
| NPS 8 | DN 200 | 832 mm | ~760 kg |
| NPS 10 | DN 250 | 991 mm | ~1240 kg |
| NPS 12 | DN 300 | 1130 mm | ~1900 kg |
Service fit
Where this valve is used
Typical applications
- Boiler drain, vent and startup lines
- Feedwater heater level control isolation
- Turbine drains and gland steam
- Soot blower and auxiliary steam isolation
- HP bypass and warm-up lines
Selection limits to check
- Full-bore requirements or line pigging - the S-shaped body restricts the bore.
- Applications that cannot tolerate the pressure drop across the seat, which is significantly higher than a gate valve of the same size.
- Reverse flow installation. Flow direction is fixed and marked on the body; installing backwards can lift the disc off the stem.
- Modulating control duty requiring a defined Cv characteristic - that is a control valve, not a hand-operated globe valve.
Quality assurance
Inspection & delivery documents
The inspection and test plan defines the agreed scope, hold points and witness points for your order.
Inspection scope
- 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
Document package
- 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
Reference framework
Applicable standards
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.
Face-to-face and end-to-end dimensions. Relevant when the valve replaces an existing one or has to drop into a fixed spool.
Butt welding end preparation, including bore and bevel geometry for the matching pipe schedule.
Flanged end dimensions and ratings, when the valve is supplied with RF or RTJ flanges rather than weld ends.
Inspection and pressure testing - which tests are mandatory, test durations and allowable leakage. We state the shell and seat test scheme on the ITP.
Alternative pressure testing scheme for steel valves, used where the project specification calls for it instead of API 598.
Marking of the body and the nameplate - size, class, material heat, figure number and flow direction where applicable.
Buying questions
Frequently asked questions
Can I throttle with this valve?
For intermittent duty such as warm-up or draining, yes - that is what the plug-type disc and hardfaced seat are for. For continuous modulation you should use a control valve with a defined trim characteristic. A globe valve held at 10 % open in wet steam will erode the seat regardless of the overlay.
Why does flow direction matter so much?
The disc is retained on the stem, not welded to it. Under-the-seat flow keeps the disc pressed onto the stem nut when closed. Installed backwards, the flow can lift the disc, cause chatter, and in the worst case detach it. Flow direction is cast or marked on the body and it is not optional.
What is the pressure drop compared with a gate valve?
Substantially higher - the flow turns twice and passes a restricted seat bore. If the hydraulic calculation for the line was done assuming a gate valve, changing to a globe valve is not a free substitution. Confirm with your process engineer before switching.
Do you supply globe valves with actuators?
Yes, with electric or pneumatic actuators sized against the differential pressure and the required stroke time. We need the design differential, not just the design pressure, to size the actuator correctly - closing against full line pressure under the seat is the governing case.