Gate Valves

Materials Used

Types

Uses

Applications

The gate valve is considered to be the most popular style of valve in the world of flow control. It is a type of valve having a gate that moves perpendicular to flow of the service and hence the name. A gate valve is usually used as a shut-off valve. In the up position, the valve is open. In the down position, the valve is closed.

It is also known by other names like knife valve or slide valve or stop or block valve as its primary purpose is to stop the flow. This valve has become an important piece of fluid control equipment for more than 150 years. In fact, this was the first valve patent issued in the United States. The gate valve has become a one-stop solution for fluid control call with relatively little basic design change

Types of gate valves:
There are two types of gate valves depending on the disc design. They are:

• Parallel gate valve: This uses a flat disc gate between two parallel seat—up upstream and downstream. Parallel gate valve is widely used the pipeline industry. Unlike the wedge gate valve, the parallel gate valve needs some assistance to seal properly which is usually done in the form of a spring loaded or mechanically activated spreading action between the two disc halves. These types of valve design can fit into angularly or asymmetric misaligned valve seats.

A diagrammatic representation of different types of pipe valves.

• Wedge-shaped gate valve:
  This type of valve is of three types:
  
  1. Solid wedge: The solid wedge is the oldest form of gate valve and a drawback to this design is that it does not have any flexibility. There is the chance of solid disc getting jammed in the seats if there is any valve body/seat distortion due to extreme temperature fluctuations.
  2. Flexible wedge: With the addition of a groove or slot around its periphery, the flexible wedge gate valve can adapt to temperature changes and adverse piping stresses without binding. This design is little easier to manufacture and is the most common type seen on commodity gate valves used in industrial applications.
  3. Split wedge: This is of a two-piece design having mating surfaces on the back side of each disc half. This allow the downward stem thrust to be uniformly transferred to the disc faces and onto the seats. This provides protection against jamming due to thermal expansion.

Designs of gate valves:
There are five popular body/bonnet joint designs in gate valves. They are:

• Screwed: This is the most simple design available and it is used for inexpensive valves.
• Union: This design allows for easier disassembly for repair and maintenance.
• Bolted-bonnet: The most popular design and used in large number of gate valves. This requires a gasket to seal the joint between the body and bonnet.
• Welded-bonnet: This is a popular design where disassembly is not required. They are lighter in weight than their bolted-bonnet counterparts.
• Pressure-seal: The higher the body cavity pressure, the greater the force on the gasket in a pressure -seal valve. They are used extensively for high-pressure high-temperature applications.

Industrial applications:
Gate valves play an important role in virtually every:

• chemical plant
• refinery
• pipeline industry
• salt working pipelines
• power industry and any other
• industrial facility in the world