A Piston Valve is a device that uses the linear motion of a piston within a chamber or cylinder to control the flow of fluid through a tube or pipe. Most of the time, these valves are used with fluids that cause excessive seat wear.
What is Valve and what are the major types of Valves?
The majority of piston valves are operated manually, however other means of actuation, such as hydraulic and electronic, are utilised on occasion. The cost is determined by the extent of the damage, which is practically difficult to estimate without physically removing the pieces and deciding which ones must be replaced. Because the valve seat and valve guide may need to be fixed, repairing a valve is more involved than just removing and replacing it.
Design of Piston Valve
To prevent leakage, the piston valve normally comprises of two sealings, upper and lower sealing rings held in place by lantern bushings. The piston side wall comes into contact with the upper sailings as the valve opens, limiting leaking across the valve stem and bonnet. As the valve is closed, the bottom surface of the piston makes contact with the lower sealing rings, resulting in a leak-proof packing of the fluid inside the pipeline. The pistons are built so that they can only move in one direction, up and down, and do not rotate with the hand wheel.
What is Pinch valve?
Although the piston of the valve moves fully upward in the open position and allows the fluid to pass linearly, turbulence develops due to sharp edges of the piston and irregularities in pipe geometry at the valve zone, causing fluid energy loss in the pipeline.
Working Principle of Piston Valve
Piston Valve fulfills its functions by inserting, lowering, and raising the piston attached to the end of a shaft into the fluid passage hole, passing through the non-metal seal packages.
How does a Piston Valve work?
A piston valve is constructed similar to a globe valve and is used to shut off and regulate. The positive shut-off is provided by these valves. The metal piston, two robust valve rings, and a metal lantern bush make up the shut-off assembly.
How to select control valve for various industries?
Which valves are used to control gas flow?
The sealing surface is formed by the outer vertical surface of the piston and the inner surfaces of the sealing rings. Unlike standard globe valves, this one has a sealing surface. The small flow segment is revealed by a displacement at the commencement of the opening. Which controls the low flow rate.
The double-disc design can be adjusted to modify the flow characteristics through the valve or to vary the functioning of the valve, for as by decreasing the response time of the valve’s action.
A piston balancing valve equalises the force exerted over the sitting area while directing it in the opposite direction.
Fluid pressure would press on the bottom of the top disc and against the top of the bottom disc in the closed position, equalising flow pressure. Even when the valve is open, there is an equalising force that keeps the valve running smoothly.
What are the piston valves parts and how are they constructed?
Piston valve parts
- Body
- Bonnet
- Piston
- Valve rings
- Lantern bush
- Spindle
- Gland
- Packing
- Handwheel
- Yoke bush
- Bonnet stud
- Gland eyebolt
Piston valves are a type of globe valve in which the typical seat and cone are replaced by a piston and lantern bush. The piston is made of chrome steel and is precisely machined; the sealing rings are frequently made of self-lubricating Teflon. The cast mostly constructs the body, which can have screwed ends, flanged ends, or butt-welding ends. The bonnet is made of the same material as the body and is bolted together. A piston seals properly with the help of two robust seats. The piston is linked to the valve stem and hand-wheel, and it passes through two sealing rings separated by a lantern bush. When assembled, the load exerted along the stem compresses the two sets of sealing rings around the piston. The upper set of sealing rings serves as traditional gland packing, while the bottom set serves as the seat. The huge sealing area between the piston and rings ensures high-level shut-off tightness. If the valve has to be serviced, all of the internals can be readily removed by unscrewing the cover bolts and removing the piston. To remove the rings and the lantern bush, use an extractor tool. This procedure can be carried out without removing the valve from the pipeline. Piston valves have a long life; however, the sealing ring may wear out after a lengthy period of operation.
What are the types of piston valves?
Types of Piston Valves are
- Single and Double Actuation Piston Valves
- Regulating and Normal Piston Valves
Single and Double Actuation Piston Valves
There are many different types of piston valves are available in the market, which can be classified based on the actuation mechanism, piston configurations, piston design, and functioning requirements. The valve can be classified as manual, electronic, or hydraulic based on its actuating method. However, manual operation is generally recommended.
The piston valve can have two main sorts of piston arrangements: single actuating piston and double actuating piston. In a single actuating piston system, only one piston is used to close or open the fluid flow. The piston in this scenario moves upward to open the flow and downward to close it.
Two pistons are included in a double actuating piston, opposing each other, with their bottom flat faces facing each other. To open the flow, both pistons move backward, creating a gap for the fluid flow; to close the flow, each piston advances towards each other, establishing total contact, and the fluid flow is completely closed. The single actuating piston valve is often operated manually, whereas the double operating piston valve is automatically operated.
Regulating and Normal Piston Valves
The piston valve is classified into two types based on its design: regulating the type and normal type. The regular kind of piston valve consists of a piston with a flat bottom face, whereas the regulating type piston has an angled bottom face. This inclination has a throttling effect on the flowing fluid and aids in fluid regulation with minimal losses.
The angle seat piston valve, in which the piston enters the flowing fluid at a specific angle, is sometimes used to include the throttling effect and smooth operation of the valve. This valve is often actuated automatically through electrical or hydraulic actuation. The operating condition categorises piston valves into two types: balanced and unbalanced. The balanced piston valve is intended for high-pressure applications, whereas the unbalanced piston valve is intended for low-pressure applications.
Application Of Piston Valve
Piston valves are typically utilised for saturated and superheated steam and hot water service in power plants, refineries, pulp and paper mills, and other similar facilities. Steam headers and manifolds, condensate manifolds, desuperheaters, steam trap isolation, etc.
What are the advantages and disadvantages of piston valves?
Advantages of piston valves
- They regulate the flow of water.
- The environmentally close contact of the metal piston to the non-metal seal packs ensures good tightness.
- Because the piston travels by sealing packs during opening and shutting, the circumference can also be utilised for liquids containing solid particles.
- They are also appropriate for gaseous fluids.
- The pistons are not easily worn since they slide in non-metal gaskets. Gaskets that have worn out can be simply replaced.
Disadvantages of piston valves
- Because of their construction, pressure losses are substantial.
- They have dead volume. Inside the valve, residues may build.
- Huge forces act on the opening and closing spindle at big nominal diameters. This force makes closing difficult.
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