OS&Y vs NRS Gate Valves: Fire Protection and Process Service
Technical guide · Supreme Valves India · Updated 2026-10-28
Direct answer: OS&Y (outside screw and yoke) gates show a rising stem so position is visible; stem threads stay outside the packing. NRS (non-rising stem) gates keep threads inside the bonnet — better for tight headroom and underground service. Fire-water and most process API 600 RFQs ask for OS&Y; NRS appears with post indicators and buried valves.
OS&Y appears ~90 times as a feature flag in our RFQ archive — it is not optional wording on most gate line lists.
Mechanical difference
| Feature | OS&Y | NRS |
|---|---|---|
| Stem motion | Rises as valve opens | Stem does not rise; handwheel may turn in place |
| Thread location | Outside, above packing | Inside, exposed to media/packing area |
| Position indication | Visual stem height | Needs indicator or post indicator |
| Headroom | Needs clearance for rising stem | Lower profile |
Fire protection
Sprinkler and hydrant control valves are often resilient-wedge OS&Y, UL Listed / FM Approved, flanged or grooved. Supervisory (tamper) switches may be required on the supervisory assembly. NRS fire valves are used with post-indicator flanges where the valve is buried or remote. Verify the exact listing covers the end type and size — a flanged listing does not cover grooved automatically.
Process and steam
API 600 WCB gates on process RFQs almost always say OS&Y bolted bonnet. Forged API 602 Class 800 gates are likewise OS&Y. NRS is uncommon on hydrocarbon process isolation unless a special installation constraint exists.
RFQ checklist
- OS&Y or NRS (and post indicator if NRS fire service)
- Resilient wedge (fire) vs metal wedge (process)
- Ends: flanged PN16 / Class 150, or grooved
- UL/FM file references if fire-water mandatory
For process tags see WCB Class 150 gate RFQ; for fire constructions see fire protection valves.
Frequently asked questions
Why do fire-water specs prefer OS&Y gates?
The rising stem shows open/closed position from a distance, which matters for fire-pump rooms and sprinkler control. Many UL/FM listed resilient-wedge gates are OS&Y constructions for that reason.
What is NRS used for?
Non-rising stem gates keep stem threads inside the valve — useful where vertical clearance is limited (underground, pits) or where a post indicator is used instead of a visible stem.
Are process API 600 gates usually OS&Y?
Yes. Most API 600 OS&Y bolted-bonnet gates for process isolation use a rising stem with the screw outside the packing, so threads are not in contact with the process fluid.