What is a Check Valve?
Check valves are the valves used to prevent fluid backflow in a pipe system. A non-return valve (NRV) is another name for a check valve. Check valves are one-way valves that open in response to fluid flow and pressure. The check valve closes to prevent pressure backflow to upstream equipment, such as the pump and compressor.
Types of Check Valves
- Swing Check Valves
- Tilting Disk Check Valves
- Wafer Check Valves
- Dual Plate Wafer Check Valves
- Spring Loaded Check Valves
- Piston Check Valves
- Ball Check Valves
- Non-Slam Check Valves
The Swing Check Valve
The swing check valve is offered in two body configurations: straight and y-pattern.
A swing check valve is made out of a valve body fitted with a disc that swings on a hinge or shaft. The disc will swing off the seat, allowing you to go ahead. When the flow is interrupted, the disc swings back onto the seat, preventing reverse flow. The swing check valve will provide relatively little fluid flow resistance.
Swing check valves are utilized in situations when the risk of pressure surges is low. A swing check valve is commonly utilized in water and wastewater applications due to its full bore opening. Swing check valves are utilized in pipe sizes of 2 inches and larger. Swing check valves can be positioned either vertically or horizontally.
Advantages
- Swing check valves have relatively little turbulence, and pressure decreases.
- Swing check valves have replaceable seat rings.
- A swing check valve’s tilted seating surface allows for simple opening at low pressures.
- Swing check valves provide positive sealing and cause less shock when closing at high pressures.
Disadvantages
- Swing check valves cannot be used in systems with pulsating flow, as continuous flapping can destroy the seating elements.
- Because of the longer disk travel and inertia of the disk, the closure response of a swing check valve is slower than that of conventional check valves.
The Tilting Disk Check Valve
The tilting disk check valves are intended to fit between two flanges, allowing for a compact installation in large-diameter applications. Tilting disk check valves can be used in either vertical or horizontal lines.
In a tilting disk check valve, a shaft holds the disk in position. On horizontal and vertical axes, the shaft is positioned eccentrically from the valve body’s center line. Because of the shaft’s twofold eccentricity, the bottom section of the disc will occupy a larger area in the flow path. As a result, the disc will begin to flow at extremely low flow rates. The tilting disk check valves respond quickly to shutting. Tilting disk check valves are ideal for pulsing flows of compressible fluids.
Advantages
- The pressure drop through tilting disk check valves is quite minimal.
- The tilting disk check valves close quickly.
- The tilting disk check valves do not stick in filthy systems, indicating that they function properly.
- The tilting disk check valves reduce the possibility of disk slamming.
Disadvantages
- In rapidly fluctuating flows, the tilting disk check valve cannot be employed.
- When the differential pressure in the tilting disk check valve is low, the seat tightness can deteriorate.
The Wafer Check Valve
The wafer check valves are designed to be tiny and slender. Wafer check valves have a swinging disk that allows or prevents fluid flow. Wafer check valves are lightweight and have found used in a variety of applications. Wafer check valves come in a variety of sizes. The wafer check valves are cost-effective.
Wafer check valves can be utilized in applications requiring little pressure loss. Wafer check valves operate with very small pressure variations. The eccentric disc shaft combination and the disc seat in wafer check valves provide a positive shut-off of the returning media. The wafer check valves can be installed between slip-on or weld-neck companion flanges of various standards.
Advantages
- The wafer check valves have a small footprint.
- The wafer check valves have low-pressure losses.
- Wafer check valves are quite inexpensive.
Disadvantages
- The wafer check valves are unsuitable for pulsating fluid flow applications.
The Dual-Plate Wafer Check Valve
The wafer check valve and the dual-plate wafer check valve are nearly identical. The dual-plate wafer check valve, on the other hand, has two spring-loaded plates hinged on a central hinge pin.
When the flow rate decreases, the plates close due to the action of the torsion spring before the reverse flow occurs. Silent and butterfly check valves are other names for dual-plate wafer check valves.
Advantages
- Double plate butt check valves are lightweight.
- Double plate butt check valves require less space.
- Dual-plate wafer check valves can handle large flow rates.
Disadvantages
- The dual-plate wafer check valves have a higher pressure drop than the others.
- Plate interference is possible in dual-plate wafer check valves.
- Low flow rates are less suitable for dual-plate wafer check valves.
The Spring-Loaded Check Valve
Spring-loaded check valves are classified into two types: in-line valves and Y-valves. In-line spring-loaded valves are frequently referred to as nozzle check valves or quiet check valves. The in-line spring-loaded valves feature a centrally directed stem-disc assembly and a compressor spring.
The fluid flow pressure should be greater than the spring force and cracking pressure for opening the spring-loaded in-line valve. When the inlet flow pressure exceeds the spring force and cracking pressure, the flow pushes the disc, enabling the flow to continue. When the intake flow pressure drops, the spring pushes the disc against the orifice, causing it to return to its original position and closing the valve.
The operation of spring-loaded y-check valves is nearly comparable to that of in-line check valves. The spring and movable disc of spring-loaded y-check valves are positioned in a ‘Y’ shape, which distinguishes them. The advantage of spring-loaded y-check valves is that they may be inspected and serviced while still connected to the system.
A spring-loaded check valve is used in low-risk applications that need 0% backflow, such as HVAC systems and sprinkler pumps.
Advantages
- The spring-loaded check valves are versatile.
- In the event of a water hammer, spring-loaded check valves are more capable of dampening any disturbing noises.
- The spring-loaded check valves provide complete sealing and prevent backflow.
Disadvantages
- The spring-loaded check valves are more expensive than other check valves.
The Piston Check Valve
Lift check valves and piston check valves are extremely similar. The piston check valve is made up of a piston and a cylinder, which offers cushioning during operation. A piston check valve’s flow characteristics are nearly equal to those of a lift check valve.
Within piping systems where flow direction is regularly changed, piston check valves are employed in conjunction with globe and angle valves. Piston check valves are found in water, steam, and air systems.
Advantages
- The piston check valves are both long-lasting and adaptable.
- The piston check valves support automatic operation.
- The piston check valves can maintain pressure.
- Piston check valves have a low pressure drop.
- There is no fluid leakage through the piston check valves.
Disadvantages
- Water hammer is a problem with piston check valves.
The Ball-Check Valves
A ball inside the ball-check valve moves up and down, allowing or blocking the flow. The ball-check valve seat is machined in such a way that it fits the ball.
The ball-check valve chamber is conical in shape to direct the ball to the seat for sealing and blocking the reverse flow. Ball-check valves are used in tiny pumps and low-head systems. Ball-check valves are effective in both water and wastewater applications.
High pressures and dynamics can cause severe slamming in ball-check valves.
Advantages
- The ball-check valves are compact.
- The ball-check valves have no external parts.
- The ball-check valves are cost-effective.
- The ball-check valves have high reliability.
Disadvantages
- In some cases, the ball-check valves lack an open-close indicator.
The Non-Slam Check Valves
With swing check valves, non-slam check valves tackle the problem of piping system stress.
In the swing check valves, the abrupt closure of the disc due to gravity will cause a pressure surge, which results in shock waves. The high-pressure shock waves can put a lot of strain on the pipe system.
The use of non-slam check valves eliminates this problem. The non-slam check valves are not affected by gravity. When the fluid’s upstream velocity drops, the spring assist on the valve begins to close the disc. As a result, when the upstream velocity reaches zero, the disc will be completely closed. The force required to produce a water hammer on both sides of the valve is likewise greatly decreased.
Advantages
- The stroke of non-slam check valves is short. As a result, non-slam check valves allow for speedy gentle shutting in the situation of abruptly reduced flow, preventing water hammering.
- The non-slam check valves minimize operational costs dramatically.
- The non-slam check valves wear down extremely slowly over time.
Disadvantages
- Non-slam check valves are not suitable for use in regions where line cleaning or maintenance necessitates line pigging.
