Electric Actuated WC6 WCB High Pressure Solid Wedge Gate Valve
What is a Gate Valve ?
A Gate valve is a linear motion on-off or shut-off valve. The gate-valve comprises of a disc or wedge having two seating surfaces that come in contact with the valve seats to form a seal for stopping the flow. The pressure differential between the upstream flow direction and downstream side of wedge causes the wedge or disc to force against the downstream seat creating more effective sealing on the downstream side of the wedge. Gate valve is not used to regulate flow as erosion of disc and seat may cause leakage. A gate valve in partially open or closed position is also susceptible to vibration.
Where quick and frequent operation is essential use of quarter turn valves such as ball valves and plug valves must be considered.
Classification of Gate Valves based on Disk or Wedge Design
Gate valves can be broadly classified based on the disk design. Gate valves are available with variety of disks.
Wedge Type Disks
- Solid Wedge
- Flexible Wedge
- Split Wedge
Advantages of Gate Valves
Some of the advantages of Gate Valves are as follows:
- Gate valves have good shut-off characteristics as the contact between the disk and seat ring extends over the entire circumference.
- The pressure drop across a gate valve is minimal as the disk offers no resistance to flow when the valve is in fully open position.
- Gate valves are bi-directional valves and can provide shut-off in either flow directions.
Disadvantages of Gate Valves
- Some of the disadvantages of Gate Valves are as follows:
- Stem travel in gate valve requires multiple turns of the handwheel or gear operator and hence longer time duration to open or shut the valve.
- As the gate or wedge must travel across the entire cross-section of the valve bore, the overall height of gate valve is larger compared to a ball valve which is a quarter turn valve and does not require vertical movement of the stem.
- Gate valves are provided with renewable seats which are usually difficult to change out in-situ.
- The valve flow characteristics of gate valve can cause high velocity of flow to occur for longer duration while the opening or closing the valve due to slow movement of wedge or gate. High velocities can cause erosion of seat and the disc thereby reducing the design life of the valve. This condition is also referred to as “wire drawing” effect.
- Gate valves are susceptible to the solid wedge or disc getting stuck between the seats due to differential contraction between the valve seats and the wedge during shutdown of high temperature piping system. The piping system needs to be reheated for the disc to travel smoothly again. This makes the gate valve unsuitable for use in piping systems subject to high fluctuations in temperature. However, this problem can be overcome by using gate valve with flexible wedges.
- Solid wedge gate valves are sensitive to thermal expansion loads or bending moments which can cause the wedge or disc to lock between the valve seats or result in improper seating of wedge between the seats and leakage across the valve seats.
- Gate valves being metal seated do not provide bubble-tight shut-off and should not be used in applications where small leakage across the seats are not permissible.