Principles of selecting gate valves
The
gate valve should be the first choice when shut-off valves need to be used for pipelines.
1. Although
gate valves are not restricted by the temperature as well as pressure, for gate valves with large nominal diameters and gate valves used under the medium and low pressure conditions, they are not as economical as butterfly valves. In addition, butterfly valves have the advantages of light weight and occupying small space.
2. There is a non-linear proportional relationship between the gate valves' opening height and circulation area. Generally,
gate valves can only be applied to fully open or closed occasions, and they should not be used as control valves.
3. With the closed valve cavities, the gate valves should not be used for viscous media conditions, low temperature medium conditions and conditions containing solid particles. For medium conditions under which the gasification of media may occur, the gate valve cavity is supposed to be equipped with the automatic pressure relief device, or the
gate valves should be replaced with globe valves or butterfly valves.
4. When there is pigging requirements, full bore flanged valves or ball valves should be used instead of gate valves.
5. The gate valves' bodies should not be lined.
6.
Gate valves can be used in conjunction with corrugated pipes, but stems of gate valves travel longer than the globe valves' stems do. Thus, it is better to used globe valves combined with corrugated pipes.
7. Compared with ball valves,
gate valves have poor flow performance, not suitable for pressure pulsation medium conditions, high pressure oxygen conditions, medium conditions under which cavitation of media, erosion, corrosion may happen.
8. There may be residual media in the gate valve cavities when work is stopped. Thus gate valves should not be used for highly toxic and highly corrosive liquid medium conditions.
9. There will be dead zones in the grooves of gate valve seats and so gate valves are not recommended for powder transportation or medium conditions where crystallization and solidification of media may occur.
Principles of selecting globe valves
Globe valves are a little bit expensive than gate valves, but a little cheaper than metal-sealed ball valves, seldom used as shut-off valves for main pipelines.
1. Although the Y-shaped
globe valves reduce the flow degree as well as resistance of media, and can be used as shut-off valves in pipelines, the shortcomings of them are still obvious, which leads them not to be the first choice of main shut-off valves.
2. Although
globe valves are almost free from temperature and pressure restrictions, they are not suitable for pipelines with DN250 (NPS10) and above DN250 (NPS10) because of the large closing force.
3. There is a linear proportional relationship between the globe valves' opening height and flow of media and so they are often used for shutting off the control valves' bypass or for the occasions such as water terminals and vent discharge terminals, which need more accurate control of flow.
4. The runner of
globe valves is complex and easy to be eroded, and thus globe valves should not be used for medium conditions containing solid particles.
5. The runner of globe valves are flanged, which means
globe valves are not recommended for pressure pulsation medium conditions, high pressure oxygen conditions and conditions with pigging requirements.
6. There are no closed valve cavities of globe valves, which makes
globe valves applicable to medium conditions under which the gasification of media may happen.
7. The globe valves' bodies should not be lined.
8. Due to the globe valves' stem traveling shortly and being the rising stem, the globe valve becomes one of the types of valves which can have good performance when they are used in conjunction with corrugated pipes.
