BS 5163 RISING STEM RESILIENT GATE VALVE PN16 STAINLESS STEEL GATE VALVE

What is Gate Valve?

A gate valve can be defined as a type of valve that used a gate or wedge type disk and the disk moves perpendicular to flow to start or stop the fluid flow in piping.

A gate valve is the most common type of valve used in any process plant. It is a linear motion valve used to start or stop fluid flow. In service, these valves are either in a fully open or fully closed position.

When the gate valve is fully open, the disk of a gate valve is completely removed from the flow. Therefore virtually no resistance to flow. Due to this very little pressure drops when fluid passes through a gate valve.

To achieve proper sealing, when the valve is fully closed, 360° surface contact is required between disk and seats.

Gate valves should not be used for regulation or throttling of flow because accurate control is not possible. The high velocity of the flow in the partially open valve may cause erosion of the disc and seating surfaces and also creates vibration and noise.

Gate Valve Parts

Here you can see the main parts of the gate valve. The disk of a gate valve is also known as a wedge. To learn about each of these parts read complete guide of valve parts.

Types of Gate Valves

There are three ways to classify the gate valve.

1. Types of Disk
   1. Solid taper wedge
   2. Flexible wedge
   3. Split wedge or Parallel disks Valve
2. Types of Body Bonnet Joint
   1. Screwed Bonnet
   2. Bolted-Bonnet
   3. Welded-Bonnet
   4. Pressure-Seal Bonnet
3. Types of Stem movement
   1. Rising Stem or OS & Y Type (Outside Stem and Screw Type)
   2. Non-rising Stem type

Solid Wedge Gate Valve

Solid wedge is the most common & widely used disk type because of its simplicity and strength. A valve with a solid wedge may be installed in any position, and it is suitable for almost all fluids. It can be used in turbulent flow also.

However, it does not compensate for changes in seat alignment due to pipe loads or thermal expansion. So, this type of disk design is most susceptible to leakage. Solid wedge is subjected to thermal locking if used in high-temperature service.

Thermal locking is a phenomenon in which wedge is stuck between the seats due to the expansion of the metal. Solid-wedge gate valves are generally used in moderate to lower pressure-temperature applications.

Flexible Wedge Gate Valve

The flexible wedge is a one-piece solid disk with a cut around the perimeter. These cuts vary in size, shape, and depth. A shallow, narrow cut on wedge perimeter gives less flexibility but retains strength. A cast-in recess or deeper and wider cut on wedge perimeter gives more flexibility but compromises the strength.

This design improves seat alignment and offers better leak tightness. It also improved performance in situations where thermal binding possible. Flexible wedges Gate valves are used in steam systems.

Thermal expansion of the steam line sometime causes distortion of valve bodies which may lead to thermal blinding. The flexible gate allows the gate to flex as the valve seat compresses due to thermal expansion of the steam pipeline and prevents thermal blinding.

The disadvantage of flexible gates is that line fluid tends to collect in the disk. These may result in corrosion and ultimately weaken the disk.

Split wedge or Parallel disks Gate Valve

Split wedge Disk consists of two solid pieces and holds together with the help of a special mechanism. You can see the same in images. In case, one-half of the disk is out of alignment; the disk is free to adjust itself to the seating surface. The split disk can be in a wedge shape or a parallel disk type.

Parallel disks are spring-loaded, so they are always in contact with seats and give bi-directional sealing. The split wedge is suitable for handling noncondensing gasses and liquids at normal and high temperatures.

Freedom of movement of the disk prevents thermal binding even though the valve may have been closed when a line is cold. This means when a line is get heated by fluid and expand it does not create thermal blinding.

Types of gate valve based on body, bonnet connection

1st is screwed bonnet: This is the simplest design available and it is used for inexpensive valves.

2nd is bolted-bonnet: This is the most popular design and used in a large number of gate valves. This requires a gasket to seal the joint between the body and bonnet.

3rd is Welded-Bonnet: This is a popular design where disassembly is not required. They are lighter in weight than their bolted-bonnet counterparts.

4th one is Pressure-Seal Bonnet: This type is used extensively for high-pressure high-temperature applications. The higher the body cavity pressure, the greater the force on the gasket in a pressure -seal valve.

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

Non-rising Stem Gate Valve or Insider Screw Valve