OS&Y vs NRS Gate Valve: What Is the Difference?

Both OS&Y and NRS are resilient-seated gate valves used to isolate fire mains and water networks. The difference is in how the stem moves, and that changes where each valve can be installed and how its position is shown.

OS&Y gate valve (Outside Screw and Yoke)

• The threaded stem sits outside the valve body, held by a yoke.
• When the handwheel opens the valve, the stem rises. A long visible stem means open; a short stem means closed.
• The stem threads are outside the water, so they are easy to inspect and lubricate.
• Needs vertical clearance above the valve for the rising stem.
• Can be fitted with a supervisory switch that reports to the fire alarm panel if the valve starts to close.
• Typical use: fire pump rooms, risers, sprinkler control stations.

NRS gate valve (Non-Rising Stem)

• The stem turns but does not rise; the gate travels up and down inside the body.
• Compact height, suitable for underground or space-limited locations.
• Its position cannot be seen from the valve itself, so in fire service it is used with a wall indicator post or vertical (post) indicator that shows OPEN or SHUT.
• Typical use: buried fire mains and yard valves, water supply networks.

Quick comparison

Which one should you choose?

Use OS&Y valves above ground where the valve must show its position directly, such as pump rooms and risers. Use NRS valves underground or where height is limited, together with an indicator post. In both cases, choose UL/FM approved models that match the design standard in the project specification, such as AWWA C515.

MECH OS&Y and NRS valves in Saudi Arabia

Fu-Mech supplies MECH UL/FM OS&Y gate valves, NRS gate valves, indicator posts and supervisory switches from stock in Riyadh. Contact us for sizes and prices.