Gate Valves: The most common, the most essential in the oil and gas industry. Positives and negatives not to be ignored
Gate valves are the simplest and the most crucial elements used in the oil and gas industry. There are few types of them but many important specifications that do define their work. As the name suggests, gate valves work essentially as a ‘gate’ in order to execute just the function of regulating fluid flow through the system. And they obviously do not work at all when a partial flow is required.
Reductive? No, qualifying and urging towards attentive selections of types and specifications of the gate valves suitable for each plant project. Let us therefore have a look through types and positives and negatives of gate valves.
Do you really know how a gate valve work?
Briefly, a gate valve works on a linear moviment to start or stop the flow of a fluid: a wedge or a knife shaped disk moves perpendicularly to the flow and regulates it. Due to its semplicity a gate valve does not require wide spaces and fits to each part of the pipe.
The shell, or body valve, is the principal part of a gate valve. Then different but specific elements contribute to the functioning:
- solid wedge
- bonnet and bonnet gasket
- body seats
- stem
- back seat
- gland follower and gland flange
- nuts (stem nut, yoke nut)
- handwheel and hand wheel nut
- stud bolts
- packing
- lubricator
Gate valves types: how to classify and choose them
There are essentially 7 types of gate valves, but we can also classify them by types of disk, type of body bonnet joint or type of stem movement.
- Wedge valves – They are the standard gate valves and work by lifting a gate wedge out of the line of a fluid.
- Knife valves – This kind of gate valves use a sharp and beveled edge wedge to allow thicker fluids to easily flow. Usually these valves are self-cleaning and we can classify them between having either a rising or non-rising stem design.
- Brass Valve – They are universally considered the most durable gate valve that best fit where problem of corrosion, temperature and high pressure are serius.
- Slide valves – We do have to prefer slide gate valves when we need to suspend the flow of a product from discharge points.
- Non-return valves – They allow fluids or gas to safely flow in just one direction when pressure conditions could reverse it.
- Extended body valves – These valves are use for tapping pressure vessels as they have a threaded or welded connection.
- Check valves – They are so called non-return valves because they have two gates: one for fluid to enter and other for fluid to leave.
Most of all we can choose gate valves by specifications of
- body material (principally ASTM, ASME, JIS, cast steel or forged steel)
- fluid they have to work with
- pressure class
- size, connection
- form (flanged, socket weld, butt weld)
Positives and negatives of gate valves: the importance of high quality materials and fabrication
Due to the work -the function and the high pressure– that valves has on everage to cope with, we can recognize some positive en less positive aspects. They motivate the importance of choosing high quality materials and fabrication.
Positive points
- low resistance to fluid flow when completely open
- they can work in both fluid directions
- gate opening or closing requires the same energy of other valves
- as the speed of closure is generally slow, using that valves does not raise physical shock to the system.
Less positive points
- They are not suited to throttling fluid flow.
- Exposition of the seals to deterioration and contamination by the fluid flow.
- This valve need a certain space to be serviced and we have to properly consider this point when choosing valves for a piping system.
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