Non-Rising Stem Gate Valve (IS&Y)
Valve Components / Valve StemDefinition
A non-rising stem gate valve — also called an inside screw or IS&Y (Inside Screw and Yoke) valve — has a stem that rotates in place without moving vertically. The handwheel rises and falls with the gate, and the threaded portion of the stem sits inside the flow medium. This compact design needs no vertical clearance above the valve, making it the default choice for underground piping, tight equipment rooms, and installations where space is limited.
Working Principle
The stem thread engages directly with the gate (wedge). When the handwheel turns, the stem rotates in the packing and the gate travels up or down along the threaded stem. Because the stem does not move axially, there is no visual indication of valve position from the stem alone. An indicator arrow or pointer on the handwheel housing is the only way to read valve status externally. The threads are submerged in the process fluid, which exposes them to corrosion, erosion, and deposition.
Key Components
| Stem | Rotates in place; thread engages the wedge internally |
| Handwheel | Rises/falls with the gate; fixed to the stem top |
| Wedge (gate) | Threaded nut integral to wedge rides on stem threads |
| Packing | Seals the rotating stem at the bonnet |
| Body & Bonnet | Same as rising-stem gate valve designs |
| Position indicator | External pointer or arrow showing open/closed status |
Types & Variants
| Feature | Non-Rising Stem (IS&Y) | Rising Stem (OS&Y) |
|---|---|---|
| Stem movement | Rotates only; no axial travel | Rises and falls visibly |
| Thread location | Inside the fluid boundary | Outside the fluid boundary |
| Space requirement | Compact — no vertical clearance needed | Requires stem-rise clearance |
| Position indication | External pointer only | Stem height is the indicator |
| Thread condition | Exposed to process media | Clean, accessible, lubricated |
| Ideal application | Underground, confined spaces | Fire protection, inspection-required |
Materials
Body materials mirror rising-stem gate valves: A216 WCB for general carbon steel, A351 CF8M for stainless, bronze per MSS SP-80 for water service. The stem material is more critical here because threads face the fluid — 13Cr (Type 410) is standard for non-corrosive services, while 316SS is necessary for corrosive media. For water service, bronze stems are common. The thread engagement area on the wedge is typically bronze or brass as a low-friction nut material.
Applicable Standards
API 600 (steel gate valves) covers both rising and non-rising stem variants. API 602 applies to compact forged gate valves, many of which are non-rising stem. MSS SP-80 governs bronze non-rising stem gate valves for water service. Underground valves typically require indicator posts (MSS SP-86) or curb boxes for above-ground access to the handwheel.
Applications
Underground water mains rely on non-rising stem gate valves accessed through curb boxes — the compact design fits in vaults without needing vertical clearance. Small-diameter process piping in tight equipment rooms often uses IS&Y valves where a rising stem would clash with structural steel or adjacent piping. Residential and commercial plumbing uses bronze non-rising stem gate valves on main water shut-offs. Any installation where vertical space is at a premium and visual position indication is not mandated by code is a candidate for the IS&Y design.
Advantages
- Compact — no vertical clearance needed above the handwheel
- Lower cost than rising-stem design in small sizes (2" and below)
- Stem not exposed to impact, weather, or vandalism
- Suitable for underground burial with curb box access
- Simple design with fewer external moving parts
Disadvantages
- No v