What is a check valve used for?
What is a check valve? Check valves are generally installed in pipelines to prevent backflow. A check valve is basically a one-way valve, in which the flow can run freely one way, but if the flow turns the valve will close to protect the piping, other valves, pumps etc.
What are the 5 types of check valves?
Most common types of Check valves are swing, lift (piston and ball), butterfly, stop and tilting-disk.
What is a check valve called?
The valve that used to prevent backflow in a piping system is known as a check valve. It is also known as a non-return valve or NRV. The pressure of the fluid passing through a pipeline opens the valve, while any reversal of flow will close the valve.
What is the difference between check valve and non-return valve?
A non-return valve lets the fluid flow in one direction. When fluid in the line reverses direction, a check valve prevents backflow by allowing flow in one direction. The check valves are usually designed for a particular pressure.
What are the three different types of check valves?
Check valves are unidirectional valves that provide unobstructed flow in one direction as long as flow pressure remains constant and protect the piping system against reverse flow. The three main types of check valves we offer are ball, piston, and stop check valves.
What type of check valve is best?
Swing check valves are the most common check valves. They are inexpensive and as they are automatic they do not require any external power or control to operate – only the flow direction determines the valve operation.
Where do you put a check valve?
0:184:41Check Valves: Various Types & How To Install | How To TuesdayYouTubeStart of suggested clipEnd of suggested clipAnd a lock line check valve the flapper is the most common style probably. Because it adds a leastMoreAnd a lock line check valve the flapper is the most common style probably. Because it adds a least amount of head pressure can be installed vertically. And horizontally. It's.
Do I need a check valve?
Check valves are an important component of every submersible pump water system. Why are check valves important? First, they allow your water system to maintain pressure when the pump shuts off. They also prevent backspin, up thrust and help minimize water hammer (more on this later!).
Why do check valves fail?
Check valve failure modes associated with wear or poor maintenance can include problems related to noise and vibration from water hammer, reverse flow, leakage or damage. Sticking valves can occur when material like scale or debris is trapped between the valve body and the moving parts such as the disc or ball.
What is the difference between check valve and control valve?
A check valve is the simplest type of directional control valve used in hydraulic systems. Check valves stop the flow of fluid in one direction and allow free flow in the opposite direction. They are also known as non-return valves.
Which way does a check valve go?
0:531:37Check valve is a must on your airline - YouTubeYouTubeStart of suggested clipEnd of suggested clipThe air check valve into the air line and you'll see that there's an angle like an arrow. And that'sMoreThe air check valve into the air line and you'll see that there's an angle like an arrow. And that's the way it goes so if it goes from the pump.
What is the purpose of a check valve?
The main purpose of a check valve is to prevent backflow in the system. Figure 1 shows an example of a check valve. A check valve relies on a pressure differential to work. They require a higher pressure on the input side of the valve than the output side to open the valve.
What are the requirements for a check valve?
Check valves have the following criteria to consider when selecting one for your application: 1 Material compatibility with the medium 2 Line size for connection points 3 Max pressure and cracking pressure requirement 4 Installation orientation horizontal or vertical 5 Envelope dimensions 6 Accessibility needs for inspections and repairs 7 Temperature (external and media)
What is duckbill valve?
Duckbill valves allow flow to proceed through a soft tube of which the end has a natural flattened shape, as seen in Figure 10. This flattened shape resembles a duck beak, hence the name of the check valve type. The flow opens the flattened end of the duckbill, permitting fluid to pass as seen in Figure 11 on the left. When pressure is removed from the inlet side, the duckbill end returns to its flattened state, thereby cutting off the flow as seen in Figure 11 on the right.
How does a lift check valve work?
A lift check valve consists of a guided disc that raises (lifts) up off of the valve seat to allow media flow. It requires a cracking pressure to overcome gravity and/or a spring and the guide keeps the disc in a vertical line, so that the disc can be re-seated with the correct alignment and seal. Most commonly, lift check valves require the media to make a 90-degree turn, as seen in Figure 6, but there are lift check valves that are in-line or at an angle. As the inlet pressure decreases below the cracking pressure or there is a backpressure, the valve will close by gravity, spring, and/or by using the backpressure. If there is no spring to assist in closing, mounting orientation in regard to gravity is important to ensure that the disc will swing shut with gravity.
What is a stop valve?
A stop check valve is typically a spring loaded y-check valve or a lift check valve, but it has a manual override feature. This allows them to function as a normal check valve and prevent backflow, however, there is an external mechanism that can be used to override it and maintain the valve in an open or closed state. Therefore, this valve can function as two valves in one. They are commonly used in power plants, boiler circulation, steam generators, turbine cooling, safety systems.
How does a ball valve work?
A ball check valve uses a free-floating or spring-loaded ball that rests on the sealing seat to close the orifice. The sealing seat is normally conically tapered in order to guide the ball into the seat and create a positive seal, thereby, stopping reverse flow. When the pressure of the fluid in the inlet side exceeds the cracking pressure, the ball is dislodged from its seat and allows flow to occur. When the inlet pressure doesn’t exceed the cracking pressure, or there is back pressure, the ball will close with the back pressure or via the spring, effectively closing the orifice.
What is a spring loaded check valve?
Common types of spring loaded in-line check valves are also called ‘nozzle check valves’ or ‘silent check valves.’. They can be installed in a vertical or horizontal orientation. However, since they are in-line to the system, they have to be fully removed from the line to be inspected and/or perform maintenance.
How are check valves selected?
Most check valves are selected qualitatively by comparing the required closing speed with the closing characteristic of the valve. This selection method leads to good results in the majority of applications.
How do check valves work?
Check valves differ significantly from gate and globe valves. Check valves are designed to prevent backflow. Backflow simply means the flow that has reversed itself within a pipe and begins to flow backward. There are many designs of check valves, but the two most common types are the swing check and the lift check. Check valves do not use handwheels to control the flow of a commodity but instead use gravity and the pressure of the commodity to operate the valve (see Figure 5.11 ).
What is a tilting disk check valve?
Tilting disk check valves are normally restricted to applications of low pressure and high flow rates, which cannot be met by the use of swing check valves. These valves cannot be used in lines that must be fully open.
What is a split disk wafer check?
The split disk wafer check consists of two spring-loaded D-shaped sealing elements mounted on a rib across the valve bore. The design reduces the weight of the disk by about 50%, compared with single-disk swing check valves. Coupled with spring loading, this valve closes very rapidly.
What happens when a check valve stops?
When the flow stops, gravity will reseat the disk or ball preventing backflow. This check valve requires the outlet end of the valve to always be installed in the up position. Some manufacturers refer to lift check valves that employ the use of a ball as a ball check valve.
What type of valve is used for lift check valves?
As with the globe valve, there is significant turbulence and pressure drop. There are two types of lift check valves: horizontal and vertical. Both of these valves use either a disk or ball and the force of gravity to close the valve in the event of reverse flow.
What is the action of the spring force on the left of a check valve?
Normally, the check valve closes under the action of the spring force on the left. When the fluid flows from right to left and the fluid pressure is greater than the cracking pressures, the spool moves off of its seat and opens the valve. An important concept in check valves is the cracking pressure, which is the minimum upstream pressure ...
What is a check valve?
Check valves are an automatic safety device that prevents backflow, ensures gases or liquids are flowing in the right direction, and creates a tight seal to prevent leaks. By controlling the flow of liquids, check valves protect pumps and compressors from serious damage. Flange Insert from Check-All-Valve.
What makes a check valve different from a normal check valve?
What makes it different from a normal check valve is a mechanism such as a lever, handwheel, stem, or other device that can permanently close the valve to stop liquid flow. When closed, the disk is prevented from moving off the seat, as can be seen in the diagram of a lift check valve and globe valve below.
What is the difference between a foot valve and a pump?
The opening of the valve is larger than the opening of the line. Foot valves keep the pump primed. When the pump is operating, suction pulls water up through the pipe and foot valve. When the pump is turned off, the water in the pipe is pulled back by the force of gravity.
What is a rubber diaphragm?
Diaphragm check valves have a rubber diaphragm or disk. The valve is centered in the seating area with the sealing surface on the inlet side of the valve and has an opening in the center. Backflow causes the rubber disk to cover the sealing opening, which closes the opening to the inlet. The video below, from ISM, offers a brief explanation of how a plastic diaphragm check valve works.
What is duckbill valve?
Duckbill check valves are made of rubber or synthetic elastomer and have the shape of a duck’s beak. The open end of the valve is stretched over the outlet to the supply line. The other end retains its normal shape. Upstream pressure forces the duckbill lips open allowing the flow. As the pressure increases, the lips open wider. As the pressure gets lower, the lips return to a flatten and close.
Why does my check valve keep chattering?
Some check valve systems have chattering caused by repeated opening and closing of the valve. This is caused by oversizing of the check valve. When installing a check valve, it has to be sized to fit the application. The disk has to be stable in the open position and make a complete seal when closed, which can prevent repeated opening and closing, fluttering, and failure of the check valve.
What is a butterfly check valve?
A butterfly check valve is also known as a dual, folding disk, double disk, or splits check valve. The halves of the disk open toward the centerline, as seen in the diagram, during the forward flow of the fluid. With reverse flow, the halves open and seal the pipe. The short distance that the halves have to travel lessens the slamming effect on the disks. Butterfly check valves operate very quietly making them ideal for heating, ventilation, and air conditioning systems.
What is a lift check valve?
A piston or a ball is usually used as a disk. Lift Check valves are particularly suitable for high-pressure service where the velocity of flow is high. The disk is perfectly set on the seat with full contact. They are suitable for installation in horizontal or vertical pipelines with upward flow. When the flow enters below ...
What is a double disc check valve?
As the name suggests, two halves of the disk move towards centreline with the forward flow and with reverse flow two halves open and rest on the seat to close the flow ( Flapping action).
What is a tilting disc valve?
The tilting disc type valve is designed to overcome some of the weaknesses of conventional swing type valves. The design of the tilting disk enables the valve to open fully and remain steady at lower flow rates and close quickly when the forwarding flow stop.
What is swing valve disc?
The disc in a swing type valve is unguided as it fully opens or closes. This Valve operates when there is flow in the line and get fully closed when there is no flow. Turbulence and pressure drop in the valve is very low. Disk and seat designs can be of metal to metal or metal to composite.
What is the angle of a swing valve?
Usually, the seat angles are in the range of 5 to 7 degrees. Larger seat angles reduce the disc travel, resulting in quick closing, thus minimizing the possibility of water hammer. A vertical seat has a 0-degree angle. The swing type valve allows full, unobstructed flow and automatically closes as pressure decreases.
How does a ball valve work?
A ball-type valve is very simple as it simply works on the principle of gravity. When there is enough pressure in the flow, it lifts the ball upward but when pressure reduced ball roll down and closed the opening.
What is the function of a non return valve?
The only function of a Non-return valve is to prevent backflow. There is no better alternative. Yes, you can choose the best NRV from the various available type that you have learned but you cannot supplement the Non-return valve with another valve.
What is a check valve?
Check Valves, also known as Non Return Valves (NRV) or One Way Valves, are automatic valves that normally allows fluid (liquid or gas) to flow through it in only one direction. Check valve open with forward flow and close against reverse flow. Check valves differ considerably from other members of the valve family and the prime function ...
What direction does a check valve work?
As Check Valve only works in one direction, it is crucial to understand the correct installation orientation. Usually there is an arrow on the valve housing to signal the flow direction. Otherwise, one will need to examine the valve to ensure it is installed in the intended flow direction.
What is duckbill check valve?
Duckbill Check Valves are unique, one-piece, elastomeric components that act as backward flow prevention devices or one-way valves or check valves. Duckbill check valve enable flow to proceed through a soft tube that feeds into the downstream side of the valve wherein back pressure collapses the tube and cuts off the flow. Duckbill check valves are of a flexible sleeve design made of quality fabric like reinforced elastomer materials for maximum resistance to corrosion and wear caused by continuous operation with abrasive slurries, sludge, or effluent.
What is a tilting disc check valve?
Tilting-Disc Check Valves have a disc-like closure member that rotates about a pivot point between the center and edge of the disc and is offset from the plane of the seat. The disc drops thereby into the seat on closing, and lifts out of the seat on opening. Because the center of gravity of the disc halves describes only a short path between the fully open and the closed positions, tilting-disc check valves are potentially fast closing. This particular valve is, in addition, spring-loaded to ensure quick response to retarding forward flow.
What causes a valve to stop reverse flow?
When the inlet pressure is no longer higher, gravity or higher downstream pressure will cause the disc to lower onto its seat, shutting the valve to stop reverse flow. Lift check valves have an advantage over most other types of check valves in that they need only a relatively short lift to obtain full valve opening.
What is cracking pressure?
Cracking Pressure – Refers to the minimum differential upstream pressure between inlet and outlet at which the valve will operate. Typically the check valve is designed for and can therefore be specified for a specific cracking pressure. Cracking pressure is also known as unseating head (pressure) or opening pressure.
Why are check valves installed in pipelines?
For this reason, check valves are installed in pipelines to prevent such a back flow and to permit the flow of product in only one direction. When the flow is moving in the proper direction, the valve remains open. When the flow reverses, the valve closes automatically.
Table of Contents
How Does A Check Valve Work?
- Cracking Pressure
A check valve requires a minimum upstream pressure (pressure differential between inlet and outlet) to open the valve and allow flow through it. This minimum upstream pressure at which the valve opening occurs is called the check valve ‘cracking pressure’. The specific cracking pressur… - Closing
If the upstream pressure ever falls below the cracking pressure or there is a back pressure (flow attempting to move from the outlet to the inlet), then the valve will close. Depending on the check valve design, the closing mechanism can change. In short, the back pressure pushes a gate, ball…
Check Valve Types
- Depending on the design of the check valve, they will operate slightly differently. The most common check valve is a spring loaded in-line check valve, however, we will discuss multiple types below.
Materials
- Brass
Brass check valves have excellent properties for applications that are using air, water, oil, or fuels. However, it is not resistant to seawater, purified water, or chlorinated water. They are less resistant to heat and corrosion compared to stainless steel and are typically used for smaller ap… - Stainless Steel
Stainless check valves have superior corrosion resistance, heat resistance, low-temperature resistance and excellent mechanical properties. For applications that don’t require high durability or resistance, it stainless steel is typically not a cost-effective solution when compared to PVC o…
Selection Criteria
- Check valves have the following criteria to consider when selecting one for your application: 1. Material compatibility with the medium 2. Line size for connection points 3. Max pressure and cracking pressure requirement 4. Installation orientation horizontal or vertical 5. Envelope dimensions 6. Accessibility needs for inspections and repairs 7. Temperature (external and med…
Applications
- Due to how check valves function, they are typically used for one of four different reasons in a variety of applications: 1. To protect equipment downstream form backflow damage 2. To prevent contamination due to reverse flow 3. To prevent siphoning 4. To keep a vacuum seal Due to their function, they are used in almost every industry. They are used on common household appliance…
Frequently Asked Questions
- What is the check valve symbol?
The check valve symbol can be seen in Figure 13. It points in the orientation that it allows the flow with a vertical line showing it doesn’t allow backflow. - What is the purpose of a check valve?
The main purpose of a check valve in a system is to prevent backflow, which could damage equipment or contaminate media upstream.
Chapter One – What Is A Check Valve?
Chapter Two – Types of Check Valves
Chapter Three – How Are Check Valves Used
Chapter Four – How Does A Check Valve Work?
Chapter Five – Advantages and Disadvantages of Check Valves
Conclusion
- Check valves are a method for controlling the flow of gases or liquids.
- Check valves are cost saving devices that prevent waste and protect equipment.
- Check valves vary according to the flow rate, media gravity and temperature, line size, pressure, and velocity of the flow, which can be seen in the chart below.
- A basic check valve has four individual parts: body, seat, disc, and cover.