When the gate valve closes, the sealing surface can be sealed only by the medium pressure, that is, the pressure of the medium pressure on the sealing surface of the gate plate to the other side of the valve seat to ensure the sealing surface, which is self-sealing. Most gate valves are forced to seal, that is, when the valve is closed, to rely on external force to force the gate to the seat to ensure the sealing surface.

      The gate of the gate valve moves linearly along with the stem. It is called the lift lever gate valve (also known as the gate valve). Trapezoidal threads are usually found on the lifting rod, turning the rotary motion into linear motion, i.e. turning the operating torque into operating thrust, through the nut at the top of the valve and the guide groove on the valve body.

      When the valve is opened, when the gate lifting height equals 1:1 times the valve diameter, the flow passage is completely unblocked, but in operation, this position can not be monitored. In practical use, the top of the valve stem is taken as the sign, that is, the position of the valve stem which can not be opened is taken as its full open position. In order to consider the locking phenomenon of temperature change, usually open to the apex position, and then back to 1/2-1 turn, as the full open valve position. Therefore, the full opening position of the valve is determined according to the location of the gate.

      Some gate valves, stem nuts located in the gate, hand wheel rotation to drive the stem rotation, and make the gate lift, this valve is called rotary stem gate valve or hidden stem gate valve.

The working principle of manual gate valve is:

      Rotate the handwheel to open and close the valve disc connected with the valve stem by threading in and out of the handwheel and the valve stem, lifting or lowering the valve disc.

The advantages of gate valves are:

      The fluid resistance is small.

      Opening and closing is more economical.

      Medium flow direction is not limited, no disturbance, no pressure reduction.

      Its shape is simple, its structure length is short, its manufacturing process is good, and its application scope is wide.

Disadvantages of gate valves:

      It is easy to cause erosion and abrasion between sealing surfaces, and maintenance is more difficult.

      Larger size, opening needs a certain space, opening and closing time is long.

      The structure is rather complicated.

      Installation and maintenance

      Attention should be paid to the following items in installation and maintenance of forged steel gate valves.

      Handwheel, handle and transmission mechanism are not allowed to be used for lifting, and no collision is strictly prohibited.

      The double gate valve should be installed vertically (that is, the valve stem is in a vertical position and the handwheel is at the top).

      Gate valves with bypass valves should be opened before opening (to balance the pressure difference between the inlet and outlet and reduce the opening force).

      The gate valve with belt transmission mechanism is installed according to the requirements of the product manual.

      If the valve is frequently switched on, lubricate at least once a month.