Basic Details of Gate Valve & It's Types.

 BASIC OF GATE VALVE & TYPES 

A valve that opens by lifting a barrier  out of the path of the fluid.
Gate valves require very little space along the pipe axis and hardly restrict the flow of fluid when the gate is fully opened.

Index:- 

1. Definition of Gate Valve.
2. Details of body Design & part of Gate Valve .
3. Working Principle of Gate Valve.
4. Types of Gate Valve.
5. Types of gate valve based on body and  bonnet connection.
6. Application of Gate Valve .
7. Advantages of Gate Valve.
8. Disadvantages of Gate Valve.

Definition Of Gate Valve .

• A gate valve is a valve with a sliding plate that controls the flow of fluid in a pipe or channel. Gate valves are usually operated using a handwheel which turns a screw to lift or lower the gate.  

• 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.

• Gate valves are either in a fully open or fully closed position.

• When the gate valve is fully open condition the disk of a gate valve is completely removed from the flow.  

• Gate valves don't be used for regulation or throttling of flow.

• The Gate valve is a linear actuating  valve used as flow isolator in a fluid pipeline.

• Gate valves use linear type of stem motion for opening and closing of a valve. 

• These valves use parallel or wedge shaped discs as closure members that provide tight sealing.

• The disc can moved up fully into the upper portion of the body and results no hindrance to the fluid flow cross section area. 

•  This makes the valve full open with very less pressure drop.

Details of body Design & part of Gate Valve .

• A gate valve consists of a valve body, seat and disc, a spindle, gland, and a wheel for operating the valve. The seat and the gate together perform the function of shutting off the flow of fluid.

      These are common parts of valve 

• wedge

• Yoke sleeve

• Gland Eye bolt

• Gland Flange.

• ductile iron valve body

• seating area

• stem (spindle)

• spindle bearing

• bonnet

• packing.

• The body is the largest element of the gate valve. 

• The bonnet is the cover for the opening in the body and is the pressure valve’s second most important boundary. Bonnets, like valve bodies, come in a variety of styles and models.

Working Principle of Gate Valve.

• Gate valves are normally operated by a handwheel, a valve T-key (wrench) or an actuator. 

• Gate valve works by lifting or pressing a rectangular or circular gate which connected by a gate stem by out of the path of the fluid by rotating the handle wheel clockwise and anticlockwise.

• When the gate valve wheel with the handle is turned, the gate or wedge moves up and down inside tha gate valve .

• When you turn the handle wheel clockwise, steam and get move downward across the fluid flow.

•  The gate is squeezed between two seats.

• There is no fluid leakage whe.n the valve is completely closed.

• The wheel is attached to a valve stem and transfers rotational energy to it. During the gate valve opening, the rotation of the handwheel turns the threads of the gate stem into the gate and vice versa for closing. 

Types of Gate Valve.

Gate valve classified on  three basis

1. Type of body bonnet joint connection

2 . Type of Gate valve disk.

3. Types of stem movement during operation.

1. Gate valve classified based on the  Body bonnet joint connection .

 A. Screwed Bonnet
B. Bolted-Bonnet
C. Welded-Bonnet
D. Pressure-Seal Bonnet

2. Gate valve classified based on the Valve Disk.

A. Solid taper wedge

B. Flexible wedge

C. Parallel disk wedge 

3. Gate valve classified based on the stem Movement during operation.

A. Non Rising stem
B. Rising stem.

1. A-Screwed  Bonnet gate valve .

They are commonly used in small size valves and provide a long-lasting leak-proof seal.This is the most basic design available, and it is used for low-cost valves.

Screwed valve have simple design.

1. B - 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.

1. C. Welded-Bonnet.

For welded bonnet valves, the bonnet is threaded in and torqued to an engineered torque value and the body bonnet joint is strength-welded, offering double protection against leakage.

• They are lighter in weight than their bolted-bonnet counterparts.

1. D. Pressure-Seal Bonnet

• This type valve is used extensively for high-pressure high-temperature applications like Refinary and oil and gas mostly .

• The higher the body cavity pressure, the greater the force on the gasket in a pressure -seal valve.

2.A. Solid taper wedge.

• Solid wedge type gate valve  is the most common & widely used this type  disk because of its simplicity and strength and long lasting.
•  A  gate 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.

2.B. Flexible wedge.

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

2.C.Parallel disk wedge .

• The Parallel Slide Gate Valves are mainly used in the field chemical, petroleum, natural gas designed to provide isolation and transmission of flow in a piping system or a component when closed, sometimes can be installed in the pump outlet for regulating or control of flow.

• The split/paraller wedge is suitable for handling noncondensing gasses and liquids at normal and high temperatures.

3.A. Non Rising stem

Non Rising stem Type Gate valve

• Non-Rising Stem means outside stem, also referred to as the rotary stem gate valve or blind stem wedge gate valve.
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3.B. Rising stem.

• Rising-stem valves are those valve designs that are operated by pushing or pulling the valve stem.

•  The valve stems do not rotate, thus the valve stems are threaded and matched to a stem nut that converts the rotational output motion of the motor actuator to linear movement of the valve stem.

Application of Gate Valve .

• Suitable for Oil, Gas, Air, Heavy liquids, Steam, Non-condensing gases, Abrasive and Corrosive liquids

• Sizes available range from standard cast configurations as small as 2″ to special fabricated valves exceeding 100″. All size of valve available .

• Standard cast configurations have ASME 125/150 bolting patterns and are rated at 150#.
• Socket or butt welding end gate valves with are commonly used in air, fuel gas, feed water, steam, lube oil, and other systems. 
• Threaded-end gate valves are suitable for use in air, gaseous, and liquid systems.
• Some special gate valve is used in slurry and powder product also such as knife gate valve

Advantages of Gate Valve.

• Gate valve provides good Pressure drop.

• Most of the gate valve are bi-directional

• They are suitable for high pressure and temperature application and required less maintenance.

• High capacity

• Tight shutoff

• Low cost

• Little resistance to flow

Disadvantages of Gate Valve.

• Gate valve cannot be used to control the flow.

• A gate valve is slow in operation. 

• Taking time in during opening and closing.

• When partially open it creates vibration and noise and Hammer effect.

• Maintenance is difficult.

• Large amounts of space are required for assembly, startup, and maintenance.

•   Gate valves leakages occur in systems where the high-temperature changes irregularly due to the load in the pipe and End of the pipe .

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