Working principles of globe valves

Globe valves, also called stop valves, are one of the most commonly used valves. Globe valves are popular for their advantages including less friction between sealing faces during turning on-off, long service life, low lifting height, convenient manufacturing and maintenance. Globe valves are not only suitable for medium or low pressure, but also suitable for high pressure. Working principles of globe valves are that depend on pressure of stem to make sealing face of disc seat with sealing face of seat tightly and prevent media from flowing through. Globe vales allow media to flow in only one direction. So globe valves have directivity when being installed. Face to face dimension of globe valves is higher that of gate valves. Meanwhile, for high fluid resistance, globe valves have poor sealing when long-time running. Globe valves are mandatory sealing valves. For that, pressure should be imposed, forcing sealing face to realize non-leakage when turning off valves. When media enter into valve from the bottom of disc, resistance which should be overcome by operating force is that thrust caused by friction between stem and packing. The force turning off valves is higher than that turning on valves. Nevertheless, diameter of stem should be large, in case of stem being bended.   

 

Categories of globe valves:

1. According to passageway direction, globe valves can be classified into:

(1) Straight-through globe valves

(2) Straight-way globe valves (Y globe valves): For straight-way globe valves (Y Globe valves), passageway of body forms an oblique line with main passageway. For this, flow condition has less destructiveness, compared with conventional globe valves and pressure through valves has relative less losses.   

(3) Angle globe valves: For angle globe valves, flow direction is changed for only once so that pressure drop through angle globe valves is less than that of conventional globe valves.

(4) Plunger globe valves: Plunger globe valves are a kind of conventional globe valves’ deformation. Disc and seat are generally based on plunger principle. Disc is polished into plunger and connects with stem. Sealing is realized by two elastic tings on plunger. The two elastic sealing is separated by a lantern ring and pressed tightly by load applied on bonnet by nut. Elastic rings are replaceable and can be made of various materials. The valves are mainly used for connecting or cutting off pipelines. However, equipped with special plunger or ring, plunger globe valves can also be used for regulating flow.

 

2. Based on position of threads on stem, globe valves can be classified into:

(1) Outside screw stem globe valves: Threads on stem are outside valve body. Stem is not eroded by media and convenient for lubrication. The structure is in common use. 

(2) Inside screw stem globe valves: Threads on stem are inside body. Threads contact with media directly and are eroded easily. The structure cannot be lubricated. The structure is suitable for small caliber and low temperature.