Gate valve main structural characteristics and role
Gate valve is a cut-off valve, sealing performance is not as good as the shut-off valve.
Gate valve’s main “duty” is to “cut off the flow”, as well as the minimum resistance.
The gate valve is fully open when the entire flow channel through when the pressure loss of the operation of the medium is minimal, its main advantage is that the fluid flow resistance is small.
The flow resistance coefficient of the ordinary gate valve is about 0.08 ~ 0.12, the gate valve is usually suitable for frequent opening and closing, and keep the gate fully open or fully closed conditions, not suitable for regulation, throttling, such as long-term use for regulation, the sealing surface is easy to be scoured by the medium wear, affecting the Seal performance.
Gate valve medium temperature, pressure, and the reliability of the use of attention should be drawn.
Gate valve in the opening and closing of the spool and seat sealing surface always contact and mutual friction, so the sealing surface is easy to wear, especially in the valve is close to the closed state, the spool before and after the pressure difference is very large, the sealing surface wear is more serious.
The gate valve sealing surface has a certain self-sealing ability, its spool by the medium pressure tightly in contact with the seat sealing surface, to achieve a tight seal does not leak.
Wedge gate valve spool slope is generally 3 ~ 6 degrees, when forced to close the spool excessive or large temperature changes are prone to jamming. Therefore, high temperature, high-pressure wedge gate valves, in the structure are taken certain measures to prevent the spool jamming.
Gate valve in the fully open the entire flow channel straight, when the medium is running the minimum pressure loss, its main advantage is the fluid flow resistance is small, ordinary gate valve flow resistance coefficient of about 0.08 ~ 0.12, the gate valve is usually applied to do not need to often open and close, and keep the gate fully open or fully closed working conditions, not suitable for regulation, throttling use.
Second, the gate valve installation instructions
1, the gate valve is usually a flange connection, special occasions are also useful for a welding connection.
2, gate valve can be installed in the horizontal pipeline or vertical pipeline, single and double gate valve should be installed in the horizontal pipeline, and the hand wheel should be located above the valve, not allowed to face downward installation. Gate valve media flow direction is not restricted.
3, for large diameter and high-pressure gate valves, the opening and closing torque are large. In order to reduce the opening and closing torque, the installation of a bypass valve can be used.
The bypass valve is installed outside the main gate valve, its import and export, and the main gate valve on both sides of the practice connection, parallel linkage. The main gate valve should be opened before the opening of the bypass valve into the valve, so that the pressure difference between the front and rear of the main gate valve gate is reduced, thereby reducing the opening torque of the main gate valve. Bypass valve caliber selection should be considered according to the main valve caliber and use requirements.
4、According to the design installation elevation, mark the vertical center line of the outlet wall and the elevation line of the bottom of the gate valve, with a deviation, not more than ±10mm, and check whether the center of the lifting hole of the gate body is aligned with the reserved support hole of the opening and closing machine.
(1) the gate valve will be lifted into place, and stand stable and solid.
(2) lift the gate valve into position against the wall, adjust the level and verticality of the gate body (the level and verticality of the bottom slot and side slot of the gate frame is not greater than 1/1000), the gate valve frame is reliably connected to the pre-built steel plate, and the secondary pouring takes effective closure measures to ensure that there is no leakage between the gate valve frame and the structure.
(3) installation of gate valve thrust screw and opening and closing machine seat, installation level and verticality in line with the design requirements, the center of the opening and closing machine and gate valve plate screw hole center should be located in the same vertical line, its verticality deviation is not more than 1/1000, and the whole deviation is less than 2mm, connecting the gate valve thrust screw to the gate plate thrust screw plate gate end as the benchmark, the gate valve thrust screw adjust vertical after fixing the opening and closing machine seat, opening and closing machine seat with pad Iron pad solid. Then the gate valve and closure machine of the second concrete pouring.
(4) Gate valve inspection.
① after the installation of the gate valve, check the installation accuracy in line with the installation requirements of the fasteners are firmly connected; check and refill the grease in the closure machine.
② opening and closing test of the gate valve under waterless conditions, to achieve flexible operation, action in place, smooth screw rotation, the door plate without jamming, sudden jump, strange sound phenomenon.
③ under the design water level, the gate valve opens and closes freely, with no sudden jump phenomenon, limit device should be sensitive, accurate, and reliable.
④ assist the supplier to carry out on-site leakage experiments in accordance with the relevant provisions, in the maximum design water level conditions, the gate valve leakage amount is in line with the provisions.