Gate valve on-off part is gate; gate moving direction is perpendicular to flow direction; gate valve can be used only for full open and full close, but not for regulating and throttling; gate valve has two sealing surfaces, normally these two sealing surfaces form the wedge type, the wedge angle is different according to the valve parameters. The wedge can be machined into one whole disc, called as solid gate; the wedge can be machined into flexible gate, in order to making up the sealing surface angle error during the machining process.
When closing the gate valve, the gate valve sealing surface can achieve sealing only depending on the medium pressure. In other words, making the gate valve sealing surface bear down onto the seat on the other side depending on the medium pressure, this sealing is called self-sealing. But most of gate valves adopt forced sealing. When gate valve closing, make gate bear down onto the seat forcibly depending on the outside force, making sure on the gate valve sealing.
The gate valve gate moves in a straight line along with the stem, this type of gate valve is called as rising stem gate valve. There are ladder-shaped threads on the stem normally, through the nut on the top of the valve and guides on the body, making the rotational motion into linear motion. In this case, it makes operating torque into operating thrust.
When opening the gate valve, the gate valve flow port is full when gate lifting height is just the gate valve nominal diameter. But during the gate valve operation, this position cannot be seen. In actual operation, it depends on the top point of the stem which is just the position that cannot move the gate valve gate as the gate valve full port position. In order to prevent of locking phenomenon because of temperature variation, it’s better turn back 1/2-1 circle after lifting onto the top of stem, being the full port position. So, the gate valve full port position is according to the gate valve position. Some gate valve nut are set onto the gate, the hand wheel turning drives the stem turning to lifting the gate, this type of gate valve is called non-rising stem gate valve.
Gate valve has the following advantages
Gate valve has small flow resistance, and gate valve sealing surfaces suffer small flow crushing and erosion.
Gate valve open or close is easy.
Gate valve flow direction is not limited, and gate valve does not turbulent flow or reduce pressure.
Gate valve structure is simple, gate valve face to face dimension is short, gate valve machining technique is good, and gate valve applicable scope is wide.
Gate valve has the following advantages
Gate valve sealing surfaces are easy to cause erosion and friction, and gate valve is difficult to repair.
Gate valve is high normally, and gate valve on-off needs bigger space and longer time.
Gate valve structure is too complicated.
Gate valve types
Gate valve can be divided into wedge type gate valve and parallel type gate valve according to gate valve sealing surfaces; wedge type gate valve can be divided into single wedge gate valve, double wedge gate valve and flexible wedge gate valve; parallel type gate valve can be divided into single parallel gate valve and double parallel gate valve. Gate valve can be divided into rising stem gate valve and non-rising stem gate valve according to threads position.
Notices for gate valve installation and repair
Gate valve hand wheel, lever or actuator cannot be used for lifting the gate valve, or gate valve hand wheel, lever or actuator is prohibited to be damaged.
Double disc gate valve should be mounted vertically (the gate valve stem is vertical, and the gate valve hand wheel is on the top of the gate valve)
Gate valve with by-pass valve should open the by-pass valve before opening the gate
valve, in order to balance the gate valve inlet & outlet differential pressure, and reduce the gate valve open strength.
Gate valve with actuator should be mounted according to product manual.
If gate valve is normally closed, should lubricate the gate valve once a month.