Stop-Check Valve
A globe body where the disc is free to lift under forward flow but can be screwed down to isolate. Two functions, one pressure boundary, one flange pair.
- Size NPS 2-16 (DN 50-400)
- Pressure class Class 900 - 2500
- Design temperature up to 620 °C / 1148 °F
- Body material A182 F22, F91, F92; A105 for lower temperature
- End connection BW to ASME B16.25, flanged RF or RTJ
Overview
Also called a screw-down non-return valve. The stem is not attached to the disc: opening the stem lets the disc lift under forward flow and reseat under reverse flow, while screwing the stem fully down forces the disc onto the seat and gives positive isolation. Classic application is the boiler outlet on installations where several boilers feed one header - each boiler needs non-return protection and the ability to be isolated for maintenance.
Target systems
- Boiler main steam outlet to a common header
- Multi-boiler and multi-HRSG installations
- Auxiliary steam headers with several sources
- Deaerator and heater steam supply from more than one source
- Use as a throttling valve. The disc is not stem-guided over its whole travel and will chatter at partial lift.
- Reverse-direction installation. Flow direction is fixed.
- Service where the non-return function must be verified independently - a stop-check does not give position feedback on the disc.
- Horizontal installation without confirming the disc guide arrangement; the standard configuration assumes a specific orientation.
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 2-16 (DN 50-400) | standard |
| Pressure class | Class 900 - 2500 | standard |
| Design temperature | up to 620 °C / 1148 °F Y-globe stop check construction. The limit is set by the body grade and the B16.34 table. | typical |
| Medium | Superheated and saturated steam | standard |
| Body material | A182 F22, F91, F92; A105 for lower temperature | standard |
| Disc | Piston or plug type, free-floating on the stem | standard |
| Trim | F6NM / 422SS, Stellite 6 hardfaced | standard |
| Bonnet | Self-energizing pressure seal | standard |
| End connection | BW to ASME B16.25, flanged RF or RTJ | standard |
| Orientation | Per approved GA drawing | per project |
Design
Free-floating disc with screw-down override
The stem contacts the disc but is not connected to it. Backed off, the disc behaves as a lift check. Screwed down, it becomes a positively seated globe valve. The transition is what makes this valve useful and also what makes it unsuitable for throttling.
Guided disc travel
The disc is guided over its lift so it does not cock in the bore under fluctuating flow. Guide clearance is recorded at assembly, because it is the parameter that determines whether the valve chatters in service.
Pressure seal bonnet
Same self-energizing arrangement as the rest of the range. On a boiler outlet valve, which sees the full startup and shutdown cycle of its boiler, the absence of a bolted joint to relax is a direct reliability benefit.
Stem sized for the closing case
The stem has to force the disc closed against full forward flow if the valve is shut while the boiler is on line. That, not the open condition, sets the stem and operator sizing.
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 | Disc (plug type) | A105 + Stellite 6 | F11 / F22 + Stellite 6 | F91 + Stellite 6 |
| 4 | Disc nut / stem coupling | A182 F6a | A182 F6a | A182 F6NM |
| 5 | Stem | A182 F6a | A182 F6a Cl.2 | A182 F6NM / 422SS |
| 6 | Bonnet | A105 / A105N | A182 F11, F22 | A182 F91, F92 |
| 7 | Pressure seal ring | Flexible graphite + SS liner | Flexible graphite + SS liner | Flexible graphite + Inconel liner |
| 8 | Thrust ring (segmental) | A105 | A182 F11 / F22 | A182 F91 |
| 9 | Retainer segments | A105 | A182 F11 / F22 | A182 F91 |
| 10 | Gland | A105 | A182 F11 / F22 | A182 F91 |
| 11 | Stem packing | Flexible graphite | Flexible graphite | Flexible graphite, low-leakage set |
| 12 | Yoke / yoke bushing | WCB / Ni-Al bronze | WCB / Ni-Al bronze | WCB / Ni-Al bronze |
| 13 | Back seat | 13Cr overlay | 13Cr overlay | Stellite overlay |
| 14 | Handwheel | Ductile iron / carbon steel | Ductile iron / carbon steel | Ductile iron / carbon steel |
| 15 | 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. |
| 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. |
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
- Disc lift and free-fall check through the full travel
- Guide clearance record at assembly
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
Is a stop-check the same as a globe valve with a check function bolted on?
No. The disc is deliberately not connected to the stem, which is a different internal arrangement from a globe valve. You cannot convert one to the other in the field, and a globe valve with the disc nut removed is a failed valve, not a stop-check.
Can I use one instead of a separate gate valve and check valve?
That is exactly the intent - one body, one pair of welds, one item to maintain. The trade-off is that you lose full-bore flow and you cannot independently verify the check function. On a boiler outlet the trade is usually worth it; on a main line where you need full-bore isolation it is not.
What orientation should it be installed in?
It depends on the disc arrangement supplied. Do not assume - the orientation is on the GA drawing, and it needs to be confirmed at the approval stage rather than discovered during installation.