Tel.: +86 188 6774 7750
E-mail: afvalve@chinavalvesmfg.com
Tel.: +86 188 6774 7750
E-mail: afvalve@chinavalvesmfg.com
A gate valve is a type of valve that uses a flat, vertical “gate” or “wedge” that is lowered or raised to start or stop the flow of a fluid. It is one of the most common valves used in industrial piping systems.
Its primary function is for on/off control, meaning it is designed to be either fully open or fully closed. It is not suitable for throttling (controlling the flow rate).
Body: The main outer shell that houses the internal parts and connects to the pipeline.
Bonnet: The cover that is bolted or screwed onto the body, containing the stem packing and providing a seal.
Stem: A threaded rod that connects the handwheel to the gate. Rotating the stem moves the gate up or down.
Rising Stem (OS & Y): The stem rises out of the bonnet as the valve is opened. This design allows for easy visual confirmation of the valve’s status.
Non-Rising Stem (NRS): The stem threads into the gate and rotates in place. The handwheel rises and falls with the stem. Used where vertical space is limited.
Gate / Wedge: The disc that blocks the flow. Common types are solid, flexible, or split wedges.
Seat: The ring-shaped surface against which the gate seals when closed. Seats can be integral to the body or made from a separate, resilient material for a better seal.
Handwheel: The wheel operated by the user to open or close the valve.
The operation is very straightforward:
To Open: The handwheel is turned counter-clockwise. This rotates the stem, which lifts the gate vertically out of the path of the fluid, allowing for full, unrestricted flow.
To Close: The handwheel is turned clockwise. This forces the gate down until it firmly seats against the two seat rings, creating a seal and blocking the flow completely.
Gate valves are classified based on the type of stem and the design of the gate/wedge.
Rising Stem (OS & Y – Outside Stem & Yoke):
Visual Indicator: You can tell if the valve is open or closed from a distance by the position of the stem.
Common Use: Preferred in most industrial applications, especially where status indication is important.
Non-Rising Stem (NRS):
Compact: Requires less vertical space as the stem does not rise.
Common Use: Ideal for underground installations or locations with limited headroom, like ships or submarines.
Solid Wedge:
The most common and robust type.
Simple, strong design.
Prone to thermal binding if the valve body and wedge expand at different rates under high temperature.
Best for: Turbulent flow, high-pressure systems, and most common fluids.
Flexible Wedge:
The wedge has a cut around its perimeter, giving it flexibility.
This flexibility helps it seal better and compensates for minor misalignments or changes in seat angle due to temperature or pipe stress.
Best for: Steam systems, systems with large temperature fluctuations.
Split Wedge (or Parallel Disk):
The gate consists of two separate pieces that seat against parallel seat faces.
The mechanism forces the disks outward against the seats when closing.
Less prone to thermal binding and is self-aligning.
Best for: Handling non-condensing gases and liquids, including corrosive fluids.
| Advantages | Disadvantages |
|---|---|
| Low Flow Resistance: When fully open, the gate is completely out of the flow path, resulting in very low pressure drop. | Not for Throttling: Using a gate valve to regulate flow can cause vibration and chatter, eroding the seating surfaces and ruining the valve. |
| Excellent Shut-Off: Provides a tight, leak-proof seal when fully closed. | Slow to Operate: Opening and closing requires many turns of the handwheel, which is slow. |
| Bi-Directional Flow: Can be installed in either flow direction. | Prone to Seat & Gate Damage: If foreign particles are in the fluid, they can groove or damage the sealing surfaces. |
| Suitable for High-Pressure Systems: Simple design handles high pressure well. | Occupies More Vertical Space: Especially the rising stem type. |
| Can be Used with a Variety of Fluids: Including water, oil, gas, steam, and corrosive fluids (with appropriate material choice). | Cavitation Risk: In partially open positions, the high-velocity flow can cause cavitation. |
Gate valves are ubiquitous in industries where a tight seal and full, unobstructed flow are required. Common applications include:
Water Supply and Wastewater Treatment Plants
Oil and Gas Pipelines (both upstream and downstream)
Power Plants (for boiler feedwater, steam lines, and turbine systems)
Chemical and Petrochemical Industries
Fire Protection Systems
Marine and Shipbuilding
This is a common point of confusion. The key difference is their purpose:
| Feature | Gate Valve | Globe Valve |
|---|---|---|
| Primary Function | On/Off Isolation | Flow Regulation (Throttling) |
| Flow Path | Straight-through; low pressure drop. | S-shaped; high pressure drop. |
| Operation Speed | Slow (many turns to open/close). | Faster (fewer turns). |
| Cost | Generally lower for large sizes. | Generally higher. |
In short: Use a gate valve to start or stop flow. Use a globe valve to control or adjust the flow rate.
