The closing valve is a plug-shaped disc that seals the surface or cone, and the disc moves along the centerline of the fluid. The valve stem movement form, has the lift pole type (the stem lift, the handwheel does not rise and fall), also has the elevating rotating rod type (handwheel and the valve stem rotates with the lift, the nut is located on the valve body). The cut-off valve is only applicable to open and full off, and is not allowed for adjustment and throttling.
The cut-off valve is a forced seal valve, so when the valve is closed, pressure must be exerted on the disc to force the sealing surface to leak. When the medium enters the valve under the disc, the operation force needs to overcome the resistance, is the valve stem and filler friction and the pressure of the media generated by the thrust, the force of the valve is greater than the opening valve, so the diameter of the stem is large, otherwise the valve stem top bending failure.Globe Valve
In recent years, from the seal of the valve, the media flow of the cut-off valve into the valve cavity above the disc, at this time under the action of medium pressure, close the valve force is small, and open the valve, the diameter of the stem can be reduced accordingly. At the same time, in the role of the media, this form of valve is also more stringent. China's valve "three to" has stipulated that the flow of the cut-off valve, the use of Top-down. When the cut-off valve is opened, the opening height of the disc is the nominal diameter of the $number, the flow has reached the maximum, indicating that the valve has reached full open position. Therefore, the full open position of the globe valve should be decided by the disc stroke.Globe Valve
The cut-off valve's holding point (1) structure is simpler than the gate valve, the manufacture and the maintenance are convenient. (2) The sealing surface is not easy to wear and abrasion, good sealing, open and close the disc and valve body seal between the no relative sliding, so wear and abrasions are not serious, good sealing performance, long service life. (3) When opening and closing, the disc travel is small, so the cut-off valve is smaller than the gate, but the structure length is longer than the gate valve. (4) The headstock moment is big, the opening and closing is laborious, the headstock time principal. (5) The fluid resistance is big, because the valve body medium channel is more tortuous, the fluid resistance is big, the power consumption is big. (6) The medium flow direction nominal pressure Pn≤16mpa, generally uses the downstream, the medium from the disc under the direction high; the nominal pressure Pn≥20mpa, generally uses the countercurrent, the medium from the disc direction is dirty. To increase the sealing energy. When used, the cut-off valve media can only flow in one direction and cannot change the flow direction. (7) The disc is often subjected to erosion when fully open.Globe Valve