1, for the size of the DN50 (2 in) or more of the manual operation of the valve, should be equipped with an elastic gate or expansion of the gate. Wedge gate valve usually without valve chamber overpressure protection
2, no protection of the Ming bar valve, not recommended for use. Because of the marine environment will be exposed to the stem and thread corrosion, the valve operation difficult and easy to damage the valve stem packing
3, with the reverse plate valve, adapted to the automatic shutdown system operation. For these valves available simple push-pull manipulator, therefore, to avoid the usual ball valve and plug valve required by the complex joystick cam. The movable parts of the valve with all the movable parts of the valve can be closed, eliminating the pollution caused by the paint and corrosion products
4, gate valve can not be used for throttling operation. Especially for fluid containing sand, throttling will damage the sealing surface
5. The operating temperature of the soft seal valve is limited by the sealing material.
Globe valve
When the operating temperature between the -29oC to 200oC. Most manual (open and closed) valve suitable for hydrocarbon and utility systems operations and used at 100oC above the ball valve, the application should carefully consider the soft sealing material temperature limits should be at 100oC above. The application of metal sealing ball valves should be considered in high temperature or abrasion more serious work, but should indicate the operation of the torque must be increased
1, there are two ball valve design, float ball and ear ball valve. Design of ball float valve, high pressure or large diameter will produce higher operating torque, but the seal better
2, the ball valve is not suitable for throttling, because the valve is partially opened, the sealing surface will be exposed to the fluid and damaged
3, for the key work should consider to buy with the ball valve seat and stem of lubricating parts, because lubrication can prevent a slight leakage, reduce operating torque, if valves are needed on off and discharge of the two functions, provide independent engine oil accessories sphere bleed hole
Check valve
The check valve has various forms: including the swing type, the lift type, the ball type, the piston type and the separation disc swing check valve. The fully open swing check valve is adapted to most of the non fluctuations.. The swing check valve is also applied to the vertical pipe (flow direction up).. And then there is a stop block valve to prevent the valve flap over top dead center and open.
Swing check valves should not be used for downward flow direction of the vertical pipe. If for low volatility, low flow, swing check valves vibration will occur and will eventually damage the sealing surface. To extend the service life, the valve can be coated with a layer of tungsten chromium cobalt alloy. In order to reduce the leakage of the valve seat, elastic seal should be used. Removable valve seat should be preferred, because they are easy to repair, and easy to replace the valve seal.
Swing check valve should choose a screw or bolt connection valve cap, so as to check and repair the valve and valve seat. In many cases, the high - pressure swing check valve can be repaired on the pipeline, its smallest size can be DN65 (2.5NPS) or DN80 (3NPS)
1, thin design of the rotary valve (save space), suitable for installation between two flanges. This type of check valve is normally not fully open, and is required to be removed from the pipe when repairing
2, double disc check valve thin small space occupation, light weight, it is often used for offshore oil. Because fatigue can cause spring failure, the double disc check valve thin can not be used for pulse operation. However, the use of no impact (or automatically) check valve or return valve can be considered
3, lift type check valve can only be used in small caliber (DN 40), high pressure pipeline on the treatment of clean fluid. Lift check valve can be designed for horizontal pipe or vertical pipe, but the two can not be interchangeable. Because the lift type check valve is usually operated by gravity, they may be blocked by paraffin or debris..
Globe valve
(1) the structure of the valve is simpler than the gate valve and is convenient for manufacturing and maintenance..
(2) the sealing surface is not easy to wear and abrasion, sealing good, open and close the valve and valve body sealing surface between no relative sliding, so wear and tear are not serious, good sealing performance, long service life.
(3) when the valve travel is small, the valve height is smaller than the valve height, but the structure length is longer than the gate valve length.
(4) the opening and closing torque, opening and closing the more laborious, opening and closing time principal.
(5) fluid resistance is large, the valve body medium channel is tortuous, fluid resistance, power consumption is large.
(6) the direction of media flow nominal pressure PN is less than or equal to 16MPa when. In general, the downstream, the media from the valve flap circulated in the direction; nominal pressure PN is equal to or more than 20MPa, the general use of countercurrent, media from the valve direction downstream. In order to increase seal can. Use, the valve can only flow in the direction of the medium can not change the direction of the flow.
(7) the valve is often eroded by the full valve.
Valve stem axis perpendicular to the valve seat sealing surface. Valve stem open or close the trip is relatively short, and has a very reliable cut off the action, making this valve suited as a medium cut off or throttle and throttle use.
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