subject: Stop Valve Basic Information [print this page] Valves open and close parts are plug-shaped stop valve flap, seal ends showed signs of flat or conical stop valve flap along the centerline of the fluid in a straight line. Stem form of exercise has lifting rod (stem down, hand the wheel does not lift), also rotating rod down (with hand wheel rotation and stop valve lift, nut located on the body). Stop valve is only applicable to fully open and fully closed, does not allow for adjustment and throttle. Valve is mandatory sealed valves, so the valve closes, the disc must exert pressure to force the sealing surface does not leak. When the medium below the flap valve into the valve 6:00, operating force required to overcome the resistance, is the stem and the packing of friction and pressure from the media generated by the thrust force than the stop valve off the stop valve opening force, Therefore, larger stem diameter, otherwise the top corner of the failures stem occurs. In recent years, the emergence of self-sealing valve, globe valve replaced by medium flow on the top flap valve into the valve chamber, when the pressure in the medium under the action of the force off valve is small, and open the valve of the force, stem diameter can be reduced. Meanwhile, the role of the media, this form of valve is also more closely. China Valves "three to" have the provisions of the flow valves, all with top-down.
Cut-off valve is opened,valve opening height for the nominal diameter of 25% to 30%, the flow has reached its maximum, that reached the fully open position the stop valve. So cut-off stop valve fully open position, the trip should be to determine the valve flap. Valve classification: According to the cut-off valve in the channel direction, divided into: straight-through valve; DC-type valve. In DC-type or Y-shaped valve, the valve body and the main channel flow into a slash, such flow state the damage is smaller than conventional valve, so the pressure loss through the valve is also a corresponding small. Angle-type valve: the roles valve, the fluid just changed one direction, so that the pressure drop through the valve structure than conventional globe valves. Plunger-type valve: This form of cut-off valve is a variant of conventional valves. In the stop valve, the stop valve disc and seat are usually designed based on the plunger principle. Polished into a flap stop valve connected between the plunger and valve stem seal is set in the plunger on the realization of the two elastomeric seals. Two elastic rings separated by a ring, and through the valve cover nut load exerted on the valve cover seals around the plunger pressure prison. Elastic ring can be replaced, you can use variety of materials, the valve is mainly used for "open" or "off", but with a special form of plunger or special ring can also be used to adjust flow.
According to the threaded valve stem position can be divided into: the stop valve stem thread: stop valve stem threads outside of the body. The advantage is that stem from media erosion, ease of lubrication, more common use of such structures. Next thread stem stop valve: stop valve stem in the stop valve body threads. This structure stem threads direct contact with the media, vulnerability to erosion, and can not be lubricated. Such structure for small caliber and high temperature areas
Stop valve has the following advantages: simple structure, manufacture and maintenance more convenient. Working stroke is small, open and close a short time. Sealing, the sealing surface between the friction force is small, longer life expectancy.
Stop valve defects are as follows: fluid resistance large force required to open and close more. Does not apply with particles, viscosity, easy to medium coke. Regulation poor performance.
Valve stem threads according to the type of location points are male, and internal threaded. Divided by the flow medium, with straight-through, DC type, and roles. The form of points by sealing stop valve, a packing seal valves and bellows sealed valve. Closing valve structure: the structure of cut-off valve in the form of a straight-through, DC and right-angle type. Straight-through processing is the most common structure, but its resistance to most fluids. DC-type fluid resistance small, more used to contain solid particles or viscosity of the fluid. By forging multi-angle-type body for small pass through the higher pressure of the valve.
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