What is A Gate Valve and How Does It Work? An-Overview

Gate valve is the most famous and common type of valve. This type of valve also knows as the sluice valve. A gate valve controls the flow of fluids by raising (opening) and lowering (closing) the disk or gate. Sluice or gate valve includes in the most common types of valves that use in different process plants. This is a linear motion valve that is used to stop or start the flow of fluids. These types of valves use for fully closed or fully opened services. Gate valves can’t be used for the regulation of fluids. Mostly, they use in the pipelines of different industries. So, the gate valve uses as a shut-off valve to close and open the fluid flow.

A Sluice valve is a general-purpose valve that operates based on the opening and closing of a disk. Since this valve disk is similar to a gate, the valve disk is perpendicular to the fluid flow path. A gate valve cannot use for fluid regulation applications as disk can damage if the disc is partially open. The high-velocity flow of the fluids in the partially open valves can create erosion on the surfaces of the disk and seat, and it also produces noise and vibration. This valve limits the pressure loss across the valve when the disc is fully open. In the fully opened or closed conditions, the disk damage chances become minimum.

gate valve

Gate valve uses when the liquid or gas flow needs to be straightened with the lowest limits. All gate valves can install in almost all directions because these have a bidirectional sealing function. If the sluice valve has a pressure relief function, it can be settled only in the arrow direction.

Gate valves come in various options like bonnet and gate designs, different materials, and sizes.

Working of Gate Valve:

A Sluice valve is a form of multi-turn valve that has a rising stem. This stem takes many turns to close or open the valve fully. It is generally used in the fully open or fully shut down condition; therefore, the flow regulation rate cannot be adjusted. Using these valves in the half-close situation can damage the disk. When we want to open the valve, we rotate to hand-wheel in the anti-clockwise direction, while when the valve needs to be closed, then rotate it clockwise. The disk acts as an opening element, which is attached to the end of the threaded rod. The disk attaches to the wedge-shaped seat of the valve body. This disk blocks flow through the valve.

As the valve completely opens, the valve disk moves up and opens; it allows fluid flow in all directions. When the gate valve is fully closed, the disk or gate fills the channel and completely stops flow through the valve. With hand-wheel valves, a steam mist on the hand-wheel denotes that either the valves are in the closed or opened situation. With the gear control valve, the top of the stem is not visible, and a separate indicator is provided if necessary.

Construction:

Gate valves are made of alloy steel, steel, bronze, cast carbon, Aluminum, bronze, and cast-iron, e.tc. It has flanged ends. The valve bonnet is made of cast iron. So be careful when checking it out. The gate valve has a disk, like a gate that attaches with a spindle that acts on the nut. The valve bonnet is selected based on the installation requirements and the valve position. The valve bonnet can be union, bolted, or screwed-in type.

The screw-in type bonnet provides a permanent pressure seal. Union bonnet uses in applications that require proper cleaning and inspection. A bolted bonnet uses high-pressure applications. The pressure-sealed bonnet is another type of valve bonnet that also uses for high-pressure purposes.

What are the Types of Gate Valve?

1) Rising and Non-rising stem gate valve:

The gate valve has a non-rising or rising stem. Large gate valves generally have a non-rising stem. As the handwheel is revolved, the valve stem is lifted off the bonnet by the handwheel. The disc position indicates by the disc, which also indicates whether the valve is close or opened. With small valves, the valve stem and wheel can lift at the same time. The stem of some gate valves does not rise. This is because the valve stems do not appear in the valve body. These gate valve types can be used when there is not sufficient space for the valve stem to protrude from the body.

2) Knife Valve:

These types of gate valve are the most common type of industrialized valves. The design of these valves minimizes contact between different valve components. So, knife valve design reduces wear and tear between its various parts. Knife valves have specific functions; for example, by preventing sliding contact among the valve gate and body, the medium discharges to form the interior of the valve, resulting in non-sliding movement. If the knife valve body bottom has solid particles, they can seal off through the bottom of the valve. These gate valve types are a one-way valve that has the function of cutting off the flowing fluid. If there is material in the knife valve seat area, it will drain and close. A knife valve can survive high rough sludge and temperatures. Knife valve uses for chemical, power, and mining operations.

3) Flexible Wedge Valve:

These valves have a solid disc with a cut around the boundary. This cut has a different depth, shape, and size. A narrow, flat cut around the wedge boundary reduces flexibility but maintains strength. Broader and deeper cuts around cast grooves or wedges provide greater flexibility but compromise strength.

This model enhances seat tightness and alignment. It also improves performance when thermal adhesion occurs. Flexible wedge valve uses in steam systems.

The thermal expansion of the steam line can deform the valve body and cause thermal blindness. The flexile gate permits the gate to bend when the valve seat is compressed by the thermal expansion of the steam tube, preventing thermal blindness.

The drawback of these gates is that fluids in the line will gather on the disc. This process can cause corrosion and eventually deteriorate the disc.

4) Wedge Gate Valve:

In these gate valve types, the valve shuts by pushing the wedge towards the equivalent taper in the valve body. A perfect seal is possible by combining the wedge shape of the valve body with the seat ring. As the valve fully opens, the back seat of the valve stem enters the bonnet bush. In the case of the actuator valve, the valve stem cannot sit entirely on the back seat to keep away damage. This valve opens completely below the travel limits and closes completely below the torque limits.

5) Parallel Slide Gate Valves:

For proper seating, it does not need wedging action. The valve is closed through two individual disks connected by a disk holder, and the springs move down in parallel to close the valve. As the valve body port seals, the valve stem plug prevents further movement. As the valve opens, the disk rises upward, and the valve stem sits back. These types of gate valve usually open and close entirely with limited movement.

6) Slab Gates:

These gate valves (also known as straight gate valves) are unitary gate valves containing bore size hole. When open, the holes coincide with the two rings of the seat. This orientation produces an even fluid flow with the least turbulence. This unique design minimizes the pressure loss of the system. The slab gate valve is best suited for transporting natural gas liquids (NGL) and crude oils. The valve seat remains clean. Though, the disk cavity can trap foreign objects. Therefore, the hole generally has a built-in plug and is used to expel accumulated debris for maintenance purposes.

Applications of Gate Valve:

  • These valves use in the pipeline industries.
  • It uses in the salt working pipeline.
  • It uses in chemical plants.
  • Gate valves use for the transportation of natural gas liquids (NGL) and crude oils.
  • It uses for corrosive liquids, steam, slurries, and gas.
  • These types of valves use in ships for steam circuit purposes.
  • Sluice or gate valve is used for high temperatures and pressure applications.
  • These valves use for almost all fluid’s applications like hydrocarbons, steams, feedwater, fuel gas and air, e.tc.

Advantages:

  • It has very low-pressure loss during operation.
  • Mostly, it can use as a bi-directional valve.
  • It is best appropriate for high temperatures and pressure applications.

Disadvantages:

  • It can’t close or open fast like a globe valve.
  • These valves require a large area for maintenance, operation, and installation.
  • It requires high torque because of the high-pressure variance across the seats.
  • These valves have a slow operation.
  • The sluice valve produces high noise and vibration when it opens partially.
  • These valves are not best for throttling.
  • Grinding and lapping repair of these valves is tough to achieve.

What is the difference between Gate and Globe Valves?

Globe Valve

Gate Valve

It uses to regulate, start or close the flow of the different fluids. It also uses to open or close the fluid flow but it can’t use for the regulation of fluids.
These valves can’t install in different directions. These valves can install in different directions.
A Globe valve has high cost than a gate valve. It has low cost than globe valves.
These valves have a high-pressure drop. These valves fairly have low-pressure loss as compared to globe valves.
They provide a good seal. They can’t provide a better seal than globe valves.
Globe valves have a fast operation than gate valves. Gates valves have a slow operation than the glob valves.
These valves have a shorter stroke. These valves have a longer stroke.

 

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