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Gate Valve

» Gate Valve

Gate Valve

Gate valve refers to a valve whose closing member (gate) moves in the vertical direction of the center line of the passage, mainly constructed by valve body, bonnet, stem gate, sealing packing, handwheel/gearbox and other components. Normally the two ends of the valve are connected to the pipeline with flange using studs and nuts.

 
Table of Content

1. Gate Valve Types

2. Configuration and Working Principle of Gate Valve

3. Gate Valve Performance

4. Main application range of gate valve

5. Installation and utilization of gate valve

6. Routine maintenance of gate valve

7. Gate valve repair

 
1. Gate Valve Types

A. There are two type of Gate Valve Based on Valve Stem designed
a. Rising stem Gate Valve

The valve’s stem nut is on the valve bonnet or bracket. It will rotate to lift (open the gate) and lowering (close the gate) of the valve stem. This type of design is widely used because the valve stem lead screw can be lubricated, and the degree of opening and closing of the gate is distinct.

rising stem gate valve

rising stem gate valve

b. Non rising stem gate valve

The stem nut is in the valve body and directly contact with the medium. The advantage of this design is that the height of the gate valve always remains the same, hence, small control unit can be installed. It is suitable for gate valves with large diameter or gate valves with limitation of space for control unit. The disadvantage of non rising stem gate valve is that the lead screw of the valve stem cannot be lubricated, and also the valve stem is directly contact with the pipeline medium which will cause erosion and damaged.

non rising stem gate valve

non rising stem gate valve

 B. There are two Gate Valve Types Based on gate configuration
a. Parallel Slide Gate Valve

Parallel slide gate valve can be divided into single gate and double gate. The sealing surface is parallel to the vertical centerline, where the gate valves with two sealing surfaces parallel to each other.

parallel slide gate valve

parallel slide gate valve

b. Wedge Gate Valve

Wedge gate valve can be divided into: single gate type, double gate type and flexible gate type. The sealing surface forms an angle with the vertical centerline, where the two sealing surfaces form a wedge shape.
 
2. Configuration and Working Principle of Gate Valve

A gate is used as open and close part of gate valve. Its movement direction is vertical to the fluid flow direction. The gate valve can only be used as shut off valve, and cannot be adjusted and throttled. There are two kinds of gate valve sealing: self-sealing and forced sealing. For Self sealing, the sealing can be established only by medium pressure, where the medium pressure is used to press the sealing surface of the gate to the valve seat on the other side to establish the sealing. Forced sealing means that when the gate valve is closed, it is necessary to force the gate plate toward the valve seat by external force to establish the sealing.

When the valve is opened, the height of the gate is equal to 1:1 of the valve diameter, the flow is unimpeded. But during operation, this position cannot be monitored. In actual application, the maximum opening of the valve stem is used as a reference, when the position is fully opened until the handwheel cannot be turned. Considering the handwheel maybe locked during temperature variation, it is advised to open to maximum position and turn back 1/2-1 turns, as a reference to the fully open position of the valve. Therefore, the position of the gate (ie, stroke) determine the fully open position of the valve.
 
3. Gate Valve Performance

1) Advantages of Gate Valve

It has low flow resistance. The wetted area of the valve body is straight-through, the medium flows in a straight line, hence the flow resistance is small.

  1. Effortless when opening and closing the gate valve. Whether it is open or closed, the movement direction of the gate is perpendicular to the flow direction of the medium
  2. The medium can flow in any direction on both sides, easy to install. The gate valve bore is symmetrical on both sides.
  3. The end to end dimension (the distance between the two connecting end faces of the shell) is short
  4. The gate valve shape is simple, the end to end dimension is short, the manufacturing process is good, and the application range is wide.
2). Disadvantages of Gate Valve
  1. Erosion and scratches are easily formed between the sealing surfaces, and maintenance is difficult.
  2. The external dimensions are large, a certain space is required for opening, and the opening and closing time is long
  3. Stem packing easily exposed.

 
4. Main application range of gate valve

  1. Oil and gas pipelines
  2. Pipeline and storage equipment for refined oil
  3. Oil and gas mining wellhead facilities
  4. Intercity gas transmission pipelines
  5. Tap water and sewage treatment project

 
5. Installation and utilization of gate valve

  1. Check the gate valve cavity and sealing surface before installation. No dirt or sand is allowed.
  2. The bolts of each connection point of the gate valve should be tightened evenly
  3. Packing shall be tighten, besides ensuring the tightness of the packing, the operationality of the gate shall be optimal for operation.
  4. Before installing the gate valve, the user must identify the gate valve type, connection size and the flow direction of the medium to ensure the gate valve is align to application requirements
  5. When installing the gate valve, the user must reserve the necessary space for the gate valve operation
  6. The wiring of the drive unit must be carried out according to the circuit diagram
  7. The gate valve must be maintained regularly, avoid any knock or hard contact to gate especially on sealing surface on gate and body.

 
6. Routine maintenance of gate valve

  1. The gate valve with a bypass valve should be opened before operating the gate valve (to balance the pressure difference between the inlet and outlet and reduce the operating force).
  2. The gate valve with actuator should be installed according to the provisions of the product instruction manual
  3. If the valve is used frequently, lubricate it at least once a month

 
7. Gate valve repair

1)Unable to operate
  1. Check if the pressure difference between both ends of the valve is too large
  2. Check whether the internal components of the gear box are damaged and the lubrication is good or not
  3. Check if the packing is compressed too tight
  4. Check if the packing is damaged or foreign material is inside the packing
  5. Check if the stem is deformed or distorted
2)Leaking at stem port
  1. Packing is not fully tightened, should tighten the bolting of gland flange until the leakage is stopped
  2. Foreign material is inside stem packing
  3. Stem packing is damaged, replace new packing
3)Seat Leakage
  1. For manual gate valve, close and open the gate valve again normally will fix the leaking problem
  2. Motorized gate valve positioning is not set to position
  3. The internal of gate valve either gate sealing surface or body seat sealing surface is damaged
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    NTGD Valve (China) Co. LTD
    North Avenue Zhuqu Town ,Weishi County, Kaifeng, Henan,P.R.China
    Email: sales@ntgdvalve.com
    Website:www.ntgdvalve.com

    NTGD Valve (UK) Co. LTD
    ADD.: 19,King Street, Gillingham, England ME7 1EO
    Email: sales@ntgd.co.uk