The opening and closing part of the gate valve is the disc, the direction of movement of the gate and is perpendicular to the direction of flow, the gate valve can only be fully open and fully closed, can not be used for adjusting and throttling.
Gate valve has two sealing surfaces, the most common mode of gate valve sealing surface formed two wedge, wedge angle with the valve stem, usually 5° for Wedge gate valve. The wedge disc can be made into a whole, called the rigid disc, also it can be made flexbile disc to improve their craft for small little deflection, to make up for the sealing surface angle deviation in the process, this The gate is called the flexible disc.
According to construct type of sealing surface configuration can be divided into wedge gate valve and parallel gate valve. The wedge gate valve can be divided into single disc, double-disc and flexible wedge gate valve; parallel-plate gate valve can be divided into single plate and double plate. According to the valve position of stem thread, it can be divided into rising stem gate valves and non-rising stem gate valve two types.
When valve closed, the sealing surface can only rely on media pressure to seal, that is only the medium pressure to the sealing surface of the ram pressure to the other side of the seat to ensure the sealing surface of the seal, which is self-sealing. Most of the valve is sealed by force, the valve is closed, we have to rely on external force to the ram pressure to the valve seat to ensure that the sealing surface of the seal.
Gate valve with the valve stem with a straight-line movement, called the lift rod valve (also called clear shot valve). Usually lift rod with trapezoidal thread, the rotary motion into linear motion through the valve at the top of the nut and the guide groove on the body, that is, the operating torque thrust into action.
When we open the valve, gate valve lift height equal to 1.1times of the valve diameter, the fluid channel is completely smooth, but at run time, this location can not be monitored. In actual use, is the culmination of the stem as a symbol, which means that the fixed position, as its fully open position. Temperature appears to consider locking phenomenon, usually open to the vertex position, then back 1/2-1 circle, as the fully open valve position. Therefore, the valve fully open position, according to gate position (ie, travel route)
The stem nut is located at the disc for some gate valves, turn the hand wheel to drive the turning of the stem to lift the disc, this valve is called the rotating rod valve or call the non-rising stem gate valve.
Principle of work for manual gate valve :
Turn the hand wheel through the stem threads so that it can be open or closed. The gate valve has the following advantages:
1. Small fluid resistance, the sealing surface is distressed by the media to brush and erosion.
2. Opening and closing is more laborsaving.
3. The medium flows unrestricted, spoiler, do not reduce the pressure.
4. Simple form, short structure length, good manufacturing processes for a wide range.
The defects of gate valve are as follows:
1. It is easily cause erosion and abrasion between the sealing surface, difficult maintenance.
2. Outline dimension is big, it needs enough space when opening and a long time to close it.
3. complex structure.
Cautions for installation and maintenance should note the following:
1. It is not allowed for lifting the hand wheel, lever and the transmission mechanism and forbid the collision.
2. Double-plate gate valve should be installed vertically (ie the stem is in a vertical position, the hand wheel is at the top).
3. It should be open the by-pass valve firstly before we open the main valve, so that to balance the inlet and outlet pressure difference and opening force.
4. Gate valve with a drive mechanism, please install according to instructions of installation.
5. If the gate valve is often used, it should be lubricated one time per months at least.