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l  Needle valve is a kind of adjustable valve, which is widely used, such as cutting distance for flame cutting, and the knob for adjusting flame temperature is needle valve. Needle valve is an important part of instrument measurement pipeline system, which mainly includes globe valve and ball valve. Its function is to open or cut off the pipeline. Needle valve spool is a very sharp cone, like a needle inserted into the seat, hence the name.

l  Stop valve, also known as shut-off valve, is a forced sealing valve, so when the valve is closed, pressure must be applied to the disc to prevent leakage of the forced sealing surface. When the medium enters the valve from below the valve disc, the resistance to be overcome by the operating force is the friction between the stem and packing and the thrust generated by the pressure of the medium. The force to close the valve is larger than that to open the valve, so the diameter of the stem should be larger, otherwise the stem will be bent.

l  Installation precautions

1. The installation position, height and direction of inlet and outlet must meet the design requirements. The direction of medium flow shall be consistent with the direction of arrow marked on the valve body, and the connection shall be firm and tight.

2. The valve must be visually inspected before installation, and the valve name plate shall comply with the provisions of the current national standard "general valve marks" GB 12220. For the valve with working pressure greater than 1.0 MPa and cut-off function on the main pipe, the strength and tightness test shall be conducted before installation, and the valve can only be used after it is qualified. During the strength test, the test pressure shall be 1.5 times of the nominal pressure, the duration shall not be less than 5min, and the valve shell and packing shall be qualified if there is no leakage. During the tightness test, the test pressure is 1.1 times of the nominal pressure, and the test duration meets the requirements of GB 50243.