Types of Mechanical Valves
Valves are mechanical devices used to control the flow of fluids or gases by opening, closing, or partially obstructing passages in a piping system. They come in various shapes, sizes, and materials, and are classified based on their functions, designs, and applications.
Some common types of valves and their applications are:
1. Ball valves
Ball valves are a type of plug valve characterized by a closing element in the shape of a ball. The circular shape of the seat ensures that pressure is distributed evenly throughout the entire ball. Soft seats that easily conform to the ball’s surface are standard on most ball valves. When it comes to sealing, the ball valve is a brilliant invention. These valves include a spherical closure unit for simple on/off control and reliable seal.
They are commonly used in applications where tight shut-off is required, such as in gas pipelines and water treatment plants.
2. Gate valves
These valves have a gate or wedge-shaped closure unit that is lowered into the flow path to shut off the flow. The closure chamber of a parallel gate valve, or slide valve, has parallel faces. This closing part might be a single disc or a pair of discs connected by a spreading mechanism.
The closing member of a wedge gate valve, as opposed to a parallel gate valve, is formed like a wedge. Metal-seated wedge gate valves are designed to seal not just against high but also low fluid pressures thanks to the wedge form, which introduces a high supplemental seating load.
They are commonly used in applications where a straight-through flow or full open or full close operation is required, such as in the oil and gas industry.
3. Globe Valves
To shut them off, globe valves have a closure member that may be shifted directly onto and off of the seat. Regardless of its actual shape, the closing member is typically referred to as a disc. This method of disc movement results in a fluctuating opening for the seat. The flow can be adjusted with the valve’s movable plug, which is housed in a globe-shaped body.
They are commonly used in applications where precise flow control is required, such as in chemical and pharmaceutical industries.
4. Check Valves
Automatic check valves allow forward flow but close off the opposite direction. This method of regulating flow is necessary for avoiding back flow, keeping the prime going after the pump has stopped, allowing reciprocating pumps and compressors to work, and stopping rotary pumps and compressors from reversing the flow and running backup equipment.
Lines that connect to a secondary system, especially if their pressure can increase above that of the primary system, may also need check valves. These valves are one-way and stop any back flow from occurring.
They are commonly used in applications where back flow can cause damage, such as in water and sewage systems. In process industry, check valves are normally applied at the discharge of pumps, compressors and at injection point where reverse flow can damage the equipment or pollute the system.
5. Butterfly Valves
To open or close the flow path, a butterfly valve’s disc-shaped closure member is turned by around 90 degrees. The first butterfly valves were crude pipeline dampers that were never meant to provide a secure seal. The butterfly valve family still relies heavily on this valve’s ancestor.
They are commonly used in applications where quick and easy operation is required and also where tight shut is not required.
6. Pinch Valves
Pinch valves, a type of flex-body valve, are opened and closed by pinching a tube. The smooth, uninterrupted flow path, free of bends and hinges, is a major benefit of this design idea. The pliable valve body can also form a tight seal around debris that has become lodged inside. Hence, foodstuffs and pharmaceuticals, as well as slurries and sediments that would clog in impeded flow pathways, can be handled safely and cleanly with the help of pinch valves. Pinch valves can tolerate even the most corrosive and abrasive fluids, depending on the construction material utilized for the valve body.
7. Diaphragm Valves
The valve body of a diaphragm valve is split into a hard and flexible part. A diaphragm serves as the closure member in a compressor and provides the flexible body portion. The stiff body component serves as the seat and may take the form of a weir across the flow channel. In the same way as, pinch valves benefit from having a flow route that is free of moving parts and crevices, diaphragm valves do as well. Hence, they can be used for applications comparable to pinch valves, such as the safe transportation of food and medicine. These valves use a movable diaphragm to control the flow rate.
They are commonly used in applications where precise flow control is required, such as in the chemical and pharmaceutical industries.
8. Pressure Relief Valves
When the pressure in a system goes over or below its typical range, a pressure relief valve opens to restore the normal pressure level in the system. In order to prevent the system pressure from rising above a predetermined normal or subnormal pressure limit, they must open at a predetermined system pressure, discharge or let in a predetermined amount of fluid, and then close once the system pressure has returned to normal. Except as allowed by the applicable Code of Practice for specific applications, pressure relief valves must be self-actuated for maximum reliability.
9. Stainless Steel Valves
Steel AISI type 304 is commonly considered of as the least corrosion-resistant alloy (18 Cr, 10 Ni). In an effort to standardize on the least corrosion-resistant alloy, valve manufacturers frequently choose AISI type 316 (18 Cr, 12 Ni, 2.5 Mo) stainless steel. When welding the valve onto the pipeline, stabilized grades are not as good as low carbon grades (less than 0.3% carbon). For fixing a casting flaw in a flanged valve, welding is the sole option. Standard carbon grades are perfectly adequate for flanged valves because repairs are made before the 1100C (2000F) water quench solution anneal.
Oil refineries, maritime construction, and breweries are frequent users of stainless steel valves.
- Valve selection handbook: engineering fundamentals for selecting manual valves.
- Valve Selection Handbook, Fifth Edition: Engineering Fundamentals for Selecting the right Valve Design.