A gate valve is also known as a Sluice valve, one of the most common valves for water supply systems. It controls the flow of media by lifting the gate up and down and is operated by rotating the stem Clockwise to close or clockwise to open direction. The gate inside the body of the gate valve is known as a wedge. When the wedge is lifted up it is in open condition and when it is lowered it is in closed condition.
Introduction to Gate valve
Gate valves should be used as shutoff valves for the flow of liquids instead of flow regulation. They are designed to operate in fully open or fully close conditions; when the valve is fully open there is very little scope of pressure drop and when it is fully closed a good sealing against pressure is observed.
Gate valves are available in various options based on materials, size, gate & bonnet designs, and pressure & temperature ratings.
Amazing Facts about Gate valve
The world’s largest Gate valve is installed in Texas which is 40 feet tall and weighs over 100 tons. It is the biggest Gate valve ever installed for the water pipeline system with 241 kilometers of pipeline having a dia of 102 inches. As such 5 gate valves are required for the IPL project with actuators mounted on it. The IPL project cost is $2B.
Technical specifications of the valves were approved by some USA’s top consulting firms like AECOM, CDM Smith, Black & Veatch, and Freese & Nichols.
Former US president Trump approved this project-integrated pipeline project (IPL) to meet the rising demands of water in long term. The water supply is sourced & managed by Tarrant regional water district (TRWD) & Dallas water utilities (DWU). The installed valve will have a lifespan of 100 yrs as said by the valve manufacturer.
Parts of Gate valve
Parts of the gate valve are as follows:
- Handwheel
- Yoke
- Stem
- Gland
- Gland packing (seal)
- Bonnet
- Backseat
- Body of the valve
- Wedge / Disc
- Seat ring
Gate valve working principal
The gate valve is designed primarily for on-off services where a fully open or fully closed direction is required. It has a common working principle in which the gate is connected by a stem or handle and it opens or closes by rotating the handle 360 degrees.
The handwheel is moved on the threaded part in an upward or downward direction in order to fully open or fully close the valve.
When the flow of fluid inside the gate valve is flowing at a high velocity, it is not recommended to put the gate valve semi-open as this will cause noise & vibration. Hence they should not be used for controlling or regulating the flow as it will cause leakage issues.
Gate valve can also be automated either with an electric or pneumatic actuator to control the flow on the other hand the manual gate valve is cost-effective since they have infrequent usage.
Types of Gate valve
Gate valve is of various types. Choosing the right type of Gate valve can save high replacement costs. Types of Gate valves are classified in three ways:
Based on the type of Disc
- Solid wedge gate valve
- Flexible wedge
- Split wedge or parallel disc valve
Based on the Body bonnet design
- Screwed bonnet design
- Bolted bonnet design
- Welded bonnet design
- Pressure-seal bonnet design
Based on the Stem movement
- Rising stem or OS & Y type (Outside stem & yolk)
- Non-rising stem type type
1. BASED ON THE TYPE OF DISC
If we talk about the gate valve based on the type of disc then again they are further classified as solid wedge gate valve, Flexible wedge gate valve, Split or Parallel disk wedge gate valve
Solid wedge gate valve:
A solid wedge gate valve is one of the most popular and widely used. Because of its simplicity and strength, it can be installed in any direction.
It is suitable for all kinds of fluids and moderate pressure conditions but it should not be used for high-pressure conditions. The high-pressure conditions can cause leakage of the valve.
In some cases, due to thermal expansion, the gate valve seat does not open and gets jammed this phenomenon is known as thermal binding.
Thermal locking or thermal binding is caused when a wedge of the gate valve is stuck between the seats due to the expansion of the metal.
Flexible wedge gate valve
A flexible wedge gate valve is a one-piece solid disc that consists of a small cut on the disk which fits the seat. Due to this cut between seat and disk we get leakage-free alignment. The cut varies in size shape and depth.
A narrow cut gives less flexibility but retains the strength whereas a wider cut gives more flexibility but compromises the strength.
This type of design improves the seat alignment and offers better leak protection.
It also prevents thermal blinding which may arise due to thermal expansion in the valve seat it allows the gate to flex in that situation.
It is used in steam applications.
The main disadvantage of the flexible gate valve is that it tends to collect at the bottom of the disk which may result in corrosion and ultimately weaken the disk over a period of time.
Split or Parallel disk wedge gate valve
A split wedge gate valve or parallel disk gate valve comprises two solid pieces and they are held together with the help of a special mechanism.
Instead of usual compression, the parallel slide gate valve closes with a sliding action which prevents sealing surfaces.
This mechanism offers better tightness to the disc on the seat ring and also a longer life to the disc and sealing surface.
When the closing action occurs it provides a cleaning function with intimate contact on the seats.
This action eliminates any impurities on the disc & seats and the sealing contact area is free from foreign particles or undesirable particles.
It also helps to reduce stress on the seat bearing which offers an excellent life span to it.
Actuator size can be small than the wedge type if you plan to fit one on it. There is very little scope of wear & tear to the trim because it requires low torque for the operation.
The split wedge gate valve is suitable for non-condensing gases and liquids both at normal and high temperatures.
2. BASED ON THE TYPE OF BONNET DESIGN
The below image shows the type of gate valve based on bonnet design.
Screwed bonnet
The design of this type of valve is screwed type. One of the most common & widely used low-cost valves. They are mostly used in small-sized valves & offer leakproof seals with a longer life span.
Bolted bonnet
In bolted bonnet arrangement the bonnet & valve body is bolted together with the help of bolts around it.
For better sealing & support a gasket is sandwiched between the bonnet & a valve body. It is one of the most common designs and is widely used as the majority of Gate valves type available.
The valve is also suitable for high-pressure applications in a larger size.
Welded bonnet
Welded bonnet gate valves are used where disassembly is not required. In other words, this type of design cannot be disassembled as it is welded. They are lightweight as compared to bolted bonnet valves.
Pressure seal Gate valve
As the name itself, this valve is designed for high pressure & high-temperature applications (more than 15 MPa).
The pressure seal bonnet design eliminates body & bonnet flanges thus reducing weight and simpler exterior design.
This type of pressure seal mechanism uses line pressure to create better sealing which ensures sealing integrity at high pressures.
It offers a very tight shutoff and is particularly used in steam, oil, gas, nuclear plants, etc.
They are available in ASME classes 600, 900, 1500 & 2500.
Standard connections offered are Buttweld as per ASME B16.25, and Flange end as per ASME 16.5 other connections are also available such as clamp upon request.
3. BASED ON TYPES OF STEM MOVEMENT
Rising stem or OS&Y type (Outside stem and york)
In the rising stem gate valve, the threaded stem of the valve is mounted with the gate part.
When it is fully open the stem moves upward in the direction from the handwheel level allowing the flow of fluid media.
When the stem is moved downwards in parallel to its handwheel then the valve is closed at this position and flow is stopped inside the valve.
The rising stem gate valve is also known as the OS&Y valve. OS&Y full form is outside stem & York.
Non-rising stem gate valve
Non-rising stem gate valve means the threaded stem of the valve does not move up and down while operating the valve. Such types of valves are well suited for those applications where installation space is limited.
Non-rising stem gate valves are well suitable for both above the ground and underground installations. This valve is also known as the insider screw valve.
