2011-12-23

一、Summary of globe valves

Globe valves are subject to compulsory sealed valve, so when the valve is closed pressure must be impressed to disc, prevent seal leakage. When the medium from below disc into valve, the operation is to overcome the resistance, which is stem and packing friction force produced by the medium pressure, the close force of the valve is larger than open force, so stem diameter should be large, otherwise it will happen stem bending fault. In recent years, since the valve seal appeared, the flow direction of medium is from upper disc into the body cavity, then above in medium pressure, close the valve force is smaller than open force of valve, the valve stem diameter can be reduced accordingly. At the same time, in effect, the form of the valve is strict. As is regulated in "thichem given", cut-off valve, using the top-down flow. Globe valve opens, disc height of open is 25% ~ 30% of nominal diameter, flow has reached the maximum, indicates the valve already in full open position. So the globe valve in full open position, should by disc trip to decide.

二、the features of globe valves

1。structure is more simple than gate valves, manufacture and repair is more convenient.
(2) sealing surface not easy wear and scratches, , good sealing, there is no relative sliding between disc and body when open, so wear and bruises are not serious, sealed performance is good, long service life.
(3)when close and open, disc trip is short, thus the height of cut-off valve is smaller than gate valves, but length of structure is longer than gate valves.
(4) moment is large, on and off is arduous, on-off time longer.
(5) fluid resistance is great, because body medium channel is tortuous, fluid resistance is large, power consumption is large.
(6) medium flow direction  when nominal pressure PN≤16MPa, generally USES downstream from disc bottom to upper, when The nominal pressurePN≥20Mpa, generally USES back flow, medium from the upper of the disc to the down. To increase the sealing performance. When using, globe valves medium only single direction, medium can not change flow direction.
(7) when full open disc often affected by erosion