What is a Gate Valve

Gate Valve

A gate valve has a flat closure element that slides into the flow stream to stop the fluid. They are one of the most commonly used valves, and are primarily used to permit or prevent the flow of liquids.

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.

Materials used:

  • Gun Metal
  • Cast Steel
  • Stainless Steel
  • Cast Iron
  • Alloy Steel
  • Brass
  • Bronze
  • Aluminum
  • Zirconium etc.

Buying tips:

  • Material
  • End connection
  • End usage
  • Sizes
  • Pressure grade
  • Standard
  • Corrosion or abrasion resistant
  • Durability

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.
Uses of gate valves:
Gate valves are useful in applications involving slurries. This is because their “gates” can move right through the slurry. Other than that, they are used in applications that involve viscous liquids like:

  • heavy oils
  • varnish
  • light grease
  • steam
  • oil
  • gas
  • natural gas
  • honey
  • molasses
  • cream non-flammable viscous liquids
  • high pressure, high temperature steam applications

Repair & Maintenance of Gate Valves:

Certain care should be taken for proper functioning of gate valves such as follows:

  • Since gate valves are used in harsh environments, these valves need to be repaired. This decision as to whether to repair or replace a gate valve usually depends on comparing the replacement cost to the repair cost. When the repair cost is more than than 50-65% of the cost of a new valve, it is better to replace the valve, unless the delivery is unacceptable.
  • For better performance, it is a good practice to use the gate valve three or four times a year.

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

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