How do piston valves work?
Piston valves are utilized as shut-off and regulating systems in the hot water and steam services. They are generally offered with globe-shaped body variants. A piston valve’s capacity to seal the actuating stem without packing or glands, as well as the valve port, through the action of the piston itself against pairs of sealing rings, is a significant advantage. With classic gate and globe valves, seats are replaced by rings.
A piston valve is a mechanical device that controls the flow of fluid via a tube or pipe by using the linear motion of a piston inside a chamber or cylinder. These valves are frequently employed with fluids that significantly increase seat wear. Piston valves are typically operated manually, however alternate actuation methods, such hydraulic and electronic, are occasionally utilized. It’s practically impossible to estimate the price without physically removing the components and figuring out which ones need to be replaced because it depends on the extent of the damage. Since the valve seat and valve guide may need to be repaired, repairing a valve is more difficult than just removing and replacing it.
Examples of Piston Valve Applications
When the temperature drops, the fluid being used may freeze or solidify, so the body should be heated in a pattern like a serpentine or jacket.
Regarding overall energy savings, it is important to keep in mind that valves have wide surfaces that will allow heat to escape into the air, and it is necessary to isolate the valves where different fluids travel from the ambient temperature.
In power plants, refineries, pulp and paper mills, etc., piston valves are generally utilized for hot water and steam service under saturated and superheated conditions.Examples of particular uses include steam desuperheaters, steam trap isolation, steam headers and manifolds, condensate manifolds, etc. Moreover, piston valves are able to handle gasses like oxygen, nitrogen, and hydrogen. They also work with different chemicals and heat transfer oils.
Tank and reactor drain valves, where the piston is referred to as a ram, are another use for piston valves. Because the piston and seal combination is self-cleaning, these valves may drain tanks that include slurries or even powders.
Design of Piston Valves
Upper and lower sealing rings that are secured in place by lantern bushings are used in piston valves. The upper sealing ring and the piston sidewall form a seal while the valve is open, preventing leaking through the stem and valve bonnet. Once more preventing any leakage through the valve, the piston seals against the bottom sealing ring when the valve is closed. The placement of the pistons is such that they only move linearly and do not rotate along with the stem.
The design of the globe-style body causes the fluid to make two quick bends in order to pass through the valve, even though the piston moves completely out of the flow stream when the valve is open, minimizing restriction of the flowing fluid. These turns cause losses through the valves that are comparable to those in globe valves, which have a similar body design.
The pistons are often made of stainless steel, whereas the seals are typically made of a variety of materials, usually metal-reinforced graphite (or, occasionally, rubber O-rings or PTFE). When the valve body is still in the pipeline, seals can be taken out and replaced.
The angle seat piston valve is another type of valve; it gets its name from the pneumatically operated piston, typically a disc or plug that closes against a seat, that is used to close and open the valve. These valves, which differ from the piston valves mentioned above and are often much smaller, are also employed in steam service. To minimize losses via the valve, this design places the valve actuator at an angle.
Advantages and disadvantages of piston valves
Advantages
They are responsible for the regulation of flow.
The environmentally tight contact between the metal piston and the non-metal seal packs ensures a satisfactory tightness.
Since the piston travels by sealing packs during opening and shutting, it can also be used for liquids containing solid particles.
They are also appropriate for glasses.
As the pistons glide in non-metal gaskets, they are not quickly worn. The replacement of worn gaskets is simple.
Disadvantages
The construction of them causes significant pressure losses.
Dead loudness is present in them. The valve may become clogged with residue.
Huge forces are applied to the opening and shutting of the spindle at huge nominal diameters. It is challenging to close due to this energy. At nominal diameters greater than DN 65, switching to “Balance piston” type valves is recommended.