The types of cast steel gate valves can be divided into wedge gate valves and wedge gate valves according to the sealing surface configuration. Wedge gate valves can also be divided into single gate type, double gate type and elastic gate type. Parallel gate valves can be divided into single and double gate valves. According to the position of the screw thread of the stem, it can be divided into two types: open stem gate valve and dark stem gate valve.

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

A cast steel gate valve whose gate plate moves in a straight line along with the stem is called an elevator gate valve. Generally, there are trapezoid thread on the lifting rod. Through the nuts on the top of the valve and the guide groove on the valve body, the rotary motion is changed into linear motion, that is, the operating torque is changed into operating thrust. When the valve is opened, the flow channel is completely unblocked when the height of the gate lift is equal to 1:1 of the valve size, but this position cannot be monitored during operation.

In practical use, the top of the stem as the mark, that is, the position of the immovable valve, as its full open position. In order to take account of the temperature change, the lock occurs, usually at the opening to the peak position, and then back 1/2 to 1 lap, as the position of the full open valve. Therefore, the full open position of the valve shall be determined by the position of the gate (i.e. > stroke).

Some gate valves, stem nuts on the gate plate, hand wheel rotation drive stem rotation, and raise the gate, this valve is called rotating stem gate valve or dark stem gate valve.

1. The installation position, height and inlet and outlet directions must meet the design requirements, and the connection should be firm and tight.

2. The handle of all kinds of manual valves installed on the insulated pipes shall not be lowered.

3. Before installing cast steel gate valve, appearance inspection must be carried out, and the valve nameplate should comply with GB 12220 of the current national standard. For valves with working pressure greater than 1.0mpa and with cut-off function on main stem pipe, strength and strict performance test should be conducted before installation. During the strength test, the test pressure is 1.5 times the nominal pressure, and the duration shall not be less than 5min. The valve housing and packing shall be qualified without leakage. During the strict test, the test pressure was 1.1 times of the nominal pressure. The test pressure shall meet the requirements of GB 50243 in the duration of the test, and shall be consistent with no leakage on the valve disc sealing surface

The article is from http://www.leahmatson.com