GATE VALVE

A gate valve is generally used to completely shut off fluid flow or, in the fully open position, provide full flow in a pipeline. Thus it is used either in the fully closed or fully open positions. A gate valve consists of a valve body, seat and disc, a spindle, gland, and a wheel for operating the valve.

WORKING OF GATE VALVE:

PARTS OF GATE VALVE

1) Bonnet :

The bonnet of a gate valve contains the moving parts and is attached to the valve body. The bonnet can be removed from the body in order to allow for maintenance and replacing parts.

2) Trim :

The trim of a gate valve contains the functioning pieces of the valve: the stem, the gate, the disc or wedge, and the seat rings.

3) Stem :

The stem of a gate valve is either a rising stem or a non rising stem. The stem is responsible for the proper positioning of the disk. Nonrising stems will almost always have a pointer-type indicator mounted onto the upper end of the stem to indicate valve position. This configuration protects the threads from carrying dirt into the packing because the stem threads are held within the boundary of the valve packing. Rising stems rise out of the flow path when the valve is opened. They can either have a stem that rises through the handwheel or have a stem that is threaded to the bonnet.

4) Seat :

The gate valve is equipped with two seats that carry out and ensure the seal with the gate. Gate valve seats are either integrated with the valve body or in the form of a seat ring. Seat rings are threaded into position or pressed into position and sealed welded to the valve body in the seat ring construction. For greater temperature service, the latter type of construction is preferred. Integral seats are made of the same material as the valve body, whereas pressed-in or threaded-in seats allow for more variation.The seat of a gate valve is either integral with the valve body or in a seat ring type of configuration. The seat ring construction is either threaded on to the body or pressed into position and the seal welded to the valve body. Pressed and welded is recommended for higher temperature applications. Press-in or threaded-in seats permit variation in the seat material verses the material of the body of the valve.

5) Actuator :

Valve actuators open and close the valve in response to a signal or manual manipulation. Most gate valves have manual actuators, such as a handwheel, because they are commonly used in applications where the valve does not need to be opened or closed often or quickly. Since gate valves are not used in throttling applications, the actuator is responsible for fully opening and fully closing the valve.

PRINCIPLE:

The body, seat, gate, stem, bonnet, and actuator are the essential components of a gate valve. The primary mechanism of operation is straightforward. Common gate valves are activated by a threaded stem that connects the actuator, e.g., handwheel or motor, to the gate. The stem is rotated by turning an actuator, which moves the gate up or down via the threads. To fully open or close the valve, it takes more than one 360° rotation. The valve opens by lifting the gate out of the flow path. As the gate is lowered to its closed position, the bore is sealed, and the valve is fully closed.

ADVANTAGES :

Good shutoff features
The body construction is simple, and the production process is more efficient
The length of the structure is rather short
The torque needed to close and open the door is minimal
Gate valves are bidirectional and hence they can be utilized in two directions
Low resistance to flow;
Pressure loss through the valve is minimal

DIS-ADVANTAGES:

They cannot be opened or closed quickly
Gate valves aren’t designed to control the flow
Gate valves often have two sealing surfaces, which makes processing, grinding, and maintenance more challenging
The abrasion and friction of the sealing surface increase while opening and shutting. Furthermore, it is possible to develop abrasions when the temperature is high
In open conditions, they are sensitive to vibration

Gate valves can be divided into two main types:

1) Parallel gate valve

2) wedge-shaped.

Material for Valve Construction

In order to select the proper valve material there are several important criteria to be considered:

1) The composition of the media in contact with all wetted (exposed) parts
2) Service temperatures
3) Operating pressures
4) Effectiveness of coating on materials
5) Material availability and cost
6) Compatibility of materials with injected media.
7) How long the valve will be exposed to the media

There are organizations dedicated to developing and maintaining standards for valves and materials in particular environments. Gate valves are available in many different materials. Valves can be specified by the National Association for Corrosion Engineers (NACE) and the American Petroleum Institute (API) for their ability to handle strong and corrosive media.

1) Valve is designed as per API 600\API 602/ BS5352/ API 603/ API6D/ IS780
2) Valve pressure temperature rating : API B16.34
3) Flange dimension is as per : ASME B16.5, B16.47
4) Face to face dimension is as per : ASME B16.10
5) Butt / Scoket weld end : ANSI B16.25 and B16.11
6) Valve Inspection & testing in accordance with : API 598

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