A Quick Guide To Understanding Gate Valve Types

Gate valves are one of the most common types of valves, using linear motion to control the flow of fluids. They are either in a fully open or fully closed position. They are suitable for all fluid services, such as air, gas, water supply, lubricating oil, steam, and hydrocarbons. Today, this article explains the common variations of gate valves.

Gate valve parts drawing

Gate valve symbol

Types of Disk

• Solid taper wedge gate valve

• Flexible wedge gate valve

• Split wedge or Parallel disks Valve gate valve

Types of Stem Movement

• Rising Stem or OS & Y Type (Outside Stem and Screw Type)

• Non-rising Stem type

Types of Body Bonnet Joint

• Screwed Bonnet

• Union Bonnet

• Bolted Bonnet

• Welded Bonnet

• Pressure-Seal Bonnet

Solid taper wedge gate valve design

It is the most commonly used in factories due to its simple structure, high strength, and flexibility for installation in any position. It is suitable for almost all liquids and is particularly effective for turbulent flow.

This is a typical gate valve, with an unobstructed flow path when fully opened. The gate is fixed to the valve stem, which is either threaded into the gate or connected by other mechanisms. When the valve is closed, the gate descends to block fluid flow, and when opened, it allows fluid to pass freely through the valve.

The disadvantage of this design is that the solid gate may get stuck in the valve seat.

Flexible wedge gate valve design

This is an integral solid disk with a cut around its perimeter, designed to improve the ability to correct angle errors or variations between the seats.

The cuts vary in size, shape, and depth. Shallow and narrow cuts on the wedge perimeter offer less flexibility but retain strength, while deeper and wider cuts provide greater flexibility but compromise strength.

Split wedge or Parallel disks Valve gate valve design

This consists of two disk structures positioned between the tapered seats inside the valve body and held together by a special mechanism.

The split disk can be in a split wedge or parallel disk form. Parallel disks are spring-loaded, ensuring constant contact with the seats and providing bi-directional sealing, while split wedges are suitable for handling non-condensing gases and liquids at normal or high temperatures.

OS & Y Gate Valve or Rising Stem (Outside Stem and Screw Type)

For a rising stem gate valve, when the handle is turned (opened), the stem rises above the valve’s handwheel, and when closed, it moves downward. This is because both the handle and stem are threaded, allowing them to interact. The yoke is a part of the rising stem valve and is mounted to the bonnet.

In the case of an outside screw design, only the smooth portion is exposed to the flow medium, and the stem rises above the handwheel. This type of valve is also known as an OS&Y valve, which stands for Outside Stem and York.

The stem’s movement provides a visual indication of the valve’s position.

Non-rising Stem Gate Valve or Insider Screw Valve

For a non-rising stem valve, there is no upward movement of the stem when the valve is opened. The stem is threaded into the disk.

As the handwheel on the stem rotates, the disk moves up or down along the threads, while the stem itself remains vertically stationary. This design is suitable for situations where space is limited and linear stem movement is not possible, and where the fluid medium does not cause erosion, corrosion, or wear to the stem material. This type of valve is also known as an inside screw valve.

Types of Body Bonnet Joint

Screwed Bonnet: The screwed connection structure is the simplest design, usually used for less expensive bronze valves that require minimal disassembly.

Union Bonnet: The union connection structure is also mainly used in bronze valves, but the union design facilitates easier repair and maintenance disassembly.

Bolted Bonnet: The bolted connection structure is the most common, with most industrial gate valves using this type. The connection between the body and bonnet in both screwed and union structures requires gasket sealing.

Pressure-Seal Bonnet: The pressure-seal connection structure relies on the medium pressure inside the valve body to seal the wedge-shaped malleable iron or ductile iron gasket between the body and bonnet. The higher the pressure inside the valve body cavity, the greater the force acting on the gasket. Pressure-seal valves are significantly lighter than bolted-bonnet designs.

Welded Bonnet: For compact steel valves sized 1/2 to 2 inches with pressure ratings between 800 and 2500 psi, welded bonnets are the most common. Similar to pressure-seal valves, welded designs are lighter than bolted-bonnet valves.

Advantages of Gate Valves

Gate valves are suitable for almost all fluid services.

They provide excellent sealing performance.

Gate valves offer bi-directional sealing, making them suitable for two-way flow and flexible installation.

They are robustly designed, making them ideal for high-pressure and high-temperature environments.

Disadvantages of Gate Valves

Gate valves open and close slowly.

They are prone to scratches and are primarily used in fully open or fully closed positions; partial opening may cause damage to the seat and gate.

Maintenance is challenging, requiring significant effort and time to repair or replace internal components.

In high-temperature applications, thermal expansion may cause the gate to bind with the seat.

These are the common variations of gate valves. TFW Valve is a professional valve manufacturer that offers a wide range of standard valves as well as custom designs to meet clients' specific requirements. For more information, please contact us.