what does a check valve look like

Where is a check valve located?

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 two types of check valves?

Types of Check valvesSwing Check valve. A basic swing Check valve consists of a valve body, a bonnet, and a disk that is connected to a hinge. ... Lift Check valve. The seat design of a lift-Check valve is similar to a Globe valve. ... Colored check valves.

How do I know if my check valve is working?

For example, failing check valves will start to vibrate and even lose some internal parts when problems begin to arise. Other symptoms of check valve failure include reverse flow and excessive component wear and damage. Check valves will also emit noises as they start to break down.

What is the check valve symbol?

An arrow or the symbol for any type of check valve (a fluidic/pneumatic logic symbol) on the outside of the body indicates flow direction. In this image, flow is from top to bottom. Some check valves will have both the logic symbol and an arrow to indicate correct orientation.

What is another name for a check valve?

A check valve, non-return valve, reflux valve, retention valve, foot valve, or one-way valve is a valve that normally allows fluid (liquid or gas) to flow through it in only one direction.

What is the most common type of check valve?

Swing check valvesSwing 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 flow and pressure determine the valve operation.

How do I know my check valve is bad?

0:322:35How to Diagnose and Replace a Bad Check Valve - YouTubeYouTubeStart of suggested clipEnd of suggested clipAnd hold your finger over the opening of the port for about 30 seconds. If you pull your finger awayMoreAnd hold your finger over the opening of the port for about 30 seconds. If you pull your finger away. And you feel suction. And hear a little pop noise that means that the check valve may be. Bad.

What happens if a check valve is bad?

Swing check valves use a hinged swinging disc to block and control the movement of fluid in a system. As they are used to prevent the reverse flow of fluids or gases, any failure can lead to leakage, loss of pressure, contamination, overflow, and, in the most severe cases, complete system failure.

What causes check valve failure?

Check Valves function properly with adequate pressure. The insufficient pressure of the fluids causes the valves to open and close frequently, resulting in wear out of the valve parts. Also, low pressure caused by clogged or wide pipelines affects the valves negatively and could lead to their failure.

What is the main purpose of a check valve?

Check valves are found in almost every industrial application acting as one-way or non-return valves. Check valves are simple devices, perform a vital function by preventing reverse flows, therefore preventing damage and ensuring efficient operations. For example, reverse flow can result in water hammer.

How much does it cost to fix a check valve?

How Much Does a Check Valve Replacement Cost? Depending on the size and kind of system, most homeowners spend between $135 and $1,000. Professional work costs between $100 and $400, while the gadget itself costs $35 to $600. A backwater or check valve should cost between $70 and $250, including installation.

What is the difference between check valve and backflow preventer?

Check valves use a hinged plug that allows water to pass through the pipeline but blocks it from coming back. Backflow preventers, on the other hand, apply an increased amount of pressure on a pipe to ensure the water can only flow one way.

What is the difference between single and double check valve?

A single check valve can be used for fluid category 2 protection, where there may be an aesthetic change such as temperature, taste or odour. A double check valve is used for fluid category 3 protection, where there is a risk of substances of low toxicity such as common disinfectants.

Can you have two check valves?

Having two check valves instead of one is useful because one check valve will still act, even if the other is stuck open. Also, the shutting of one valve reduces the pressure differential across the other, allowing a more dependable seal and circumventing any sort of leak.

What is the difference between a dual check valve and a double check valve?

A dual check valve is similar to a double check valve in that it is a mechanical backflow preventer consisting of two independently acting, spring-loaded check valves. However, it usually does not include shutoff valves, may or may not be equipped with test cocks or ports, and is generally less reliable than a DC.

What are double check valves used for?

A double check valve or double check assembly (DCA) is a backflow prevention device designed to protect water supplies from contamination.

What are the characteristics of check valves?

Check valves have “Dynamic Characteristics”, ie different speeds of response, which determines the maximum reverse velocity, Vr max, and, hence, the degree of “check valve slam”.

Why do we need a check valve?

The only purpose of the check valve is to prevent flow reversal or back-flow ...

What is a swing check valve?

A swing check valve is the most widely used check valve. The closing member or the disc swings on a hinge or shaft. To allow the flow, the disc swings off the seat and it swings back onto the seat to block the reverse flow. In an open position, a swing check valve offers very little resistance to the flow. To achieve optimum performance, often a lever and weight or a lever and spring are mounted. The disc weight and the return flow has an impact on the shut-off characteristics of the valve. Swing Check Valve is also known as the Tilting Disc Check valve.

Why use a diaphragm check valve?

Due to very low cracking pressure, Diaphragm check valves finds its use in low pressure and vacuum applications.

What is the minimum upstream pressure required for a check valve to open?

For a check valve to open, it must attain a minimum upstream pressure known as cracking pressure. Depending on the check valve design and size, the cracking pressure changes.

What does it mean when a check valve is closed?

In situations, if downstream pressure is more, the valve will close preventing back-flow. Closure can also be accomplished by the weight of the check mechanism, by a spring, or by a combination of all these means.

What is an in line valve?

In-line valves are also known as Nozzle Check Valves or Silent Check Valves. These valves employ a centrally guided stem-disc assembly along with a compression spring. To open the valve, the flow pressure must be more than the spring force and cracking pressure. In that case, the flow pushes the disc allowing the flow.

What is a check valve made of?

These valves can wear out or can generate the cracks after prolonged usage and therefore they are mostly made of plastics for easy repair and replacements.

Why is a check valve a two way valve?

It is a two-way valve because it contains two ports. Figure shows the graphical symbol of a check valve along with its no-flow and free-flow directions. Symbol Of Check Valve: symbol of check valve.

Where does fluid flow in a poppet check valve?

Fluid flows through the valve in the space between the seat and poppet. In the free flow direction, the fluid pressure overcomes the spring force. If the flow is attempted in the opposite direction, the fluid pressure pushes the poppet in the closed position. Therefore, no flow is permitted. poppet check valve -types of check valve.

Do you need poppets for multiport valves?

Generally individual poppets are required for each flow path that significantly increases the complexity of multi-port valves.

What are check valves made of?

The bodies (external shells) of most check valves are made of plastic or metal. An important concept in check valves is the cracking pressure which is the minimum differential upstream pressure between inlet and outlet at which the valve will operate.

Why do we need a check valve?

A check valve is installed on each of the individual gas streams to prevent mixing of the gases in the original source. For example, if a fuel and an oxidizer are to be mixed, then check valves will normally be used on both the fuel and oxidizer sources to ensure that the original gas cylinders remain pure and therefore nonflammable.

What is a swing check valve?

A swing check valve or tilting disc check valve is a check valve in which the disc, the movable part to block the flow, swings on a hinge or trunnion, either onto the seat to block reverse flow or off the seat to allow forward flow. The seat opening cross-section may be perpendicular to the centerline between the two ports or at an angle. Although swing check valves can come in various sizes, large check valves are often swing check valves. A common issue caused by swing check valves is known as water hammer. This can occur when the swing check closes and the flow abruptly stops, causing a surge of pressure resulting in high velocity shock waves that act against the piping and valves, placing large stress on the metals and vibrations in the system. Undetected, water hammer can rupture pumps, valves, and pipes within the system.

Why do you need a check valve for rainwater harvesting?

Rainwater harvesting systems that are plumbed into the main water supply of a utility provider may be required to have one or more check valves fitted to prevent contamination of the primary supply by rainwater.

What is a ball valve?

A ball check valve is a check valve in which the closing member, the movable part to block the flow, is a ball. In some ball check valves, the ball is spring -loaded to help keep it shut.

What does the check valve symbol on a piping diagram mean?

Check valve symbol on piping and instrumentation diagrams. The arrow shows the flow direction.

What is cracking pressure?

Cracking pressure – Refers to the minimum pressure differential needed between the inlet and outlet of the valve at which the first indication of flow occurs (steady stream of bubbles). Cracking pressure is also known as unseating head (pressure) or opening pressure.

How does a check valve work?

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 pressure changes based on the valve design and size, so ensure that your system can generate this cracking pressure and that it is suitable for the application.

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.

Why doesn't my check valve work?

When a check valve doesn’t work, it allows backflow. Three possible reasons for this are: sticking, leakage, or slow closing. If there isn’t a filter in the line, dirt or debris can be trapped between the disc and body keeping it open. Due to wear or corroding media on the material, the disc or seat can become damaged or torn preventing a proper seal and allowing backflow. If the valve closes too slow, minimal backflow can enter before a proper seal can occur. Ensure that gravity is helping the design, and/or your spring is quick enough to close the valve rapidly.

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 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.

What is a spring loaded Y check valve?

Spring loaded y-check valves operate very similar to in-line spring loaded check valves. The difference is that the spring and movable disc are positioned at an angle. This creates a ‘y’ shape, hence the name of the valve. It works the exact same as an in-line valve, but since the moveable components are at an angle it can be inspected and serviced while it is still connected to the system. However, they are larger and take up more room within the system.

What is the minimum upstream pressure required for a check valve?

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 pressure changes based on the valve design and size, so ensure that your system can generate this cracking pressure and that it is suitable for the application.

How does a check valve work?

Check valves quite often rely on pressure differential to work. This means that they require a higher pressure on the input side of the valve than on the output side of the valve in order to open the valve.

What are check valves used for?

Check valves are also used in many fluid systems, such as those in chemical and power plants. Typical applications in the nuclear industry include feedwater control systems; dump lines; make-up water; miscellaneous process systems; N2 systems; and monitoring and sampling systems. In aircraft and aerospace, check valves are used where high vibration, large temperature extremes and corrosive fluids are present.

What type of pump uses a check valve?

Check valves are used with some types of pumps. Piston-driven and diaphragm pumps, such as metering pumps and pumps for chromatography, commonly use inlet and outlet ball check valves. These valves often look like small cylinders attached to the pump head on the inlet and outlet lines. Many similar pump-like mechanisms for moving volumes of fluids around use check valves such as ball check valves.

Why do we need a check valve?

A check valve is installed on each of the individual gas streams to prevent mixing of the gases in the original source. For example, if a fuel and an oxidiser need to be mixed, then check valves will normally be used on both the fuel and oxidiser sources to ensure ...

What is a ball valve?

A ball check valve is a check valve in which the closing member, the movable part to block the flow, is a spherical ball. Whereas a diaphragm check valve uses a flexing rubber diaphragm positioned to create a normally-closed valve.

What is Parker C series check valve?

Parker C Series Check Valves are designed for unidirectional flow control of fluids and gases in industries such as chemical processing, oil and gas production and transmission, pharmaceutical, pulp and paper, power and utilities. They feature resilient, custom moulded, blow-out resistant seat design and a back stopped poppet that minimises spring stress.

Do check valves have a handle?

They work automatically and therefore most do not have any valve handle or stem. The bodies (external shells) of most check valves are made of plastic or metal.

What is a Check Valve?

A check valve is a mechanical device used to stop the backflow of the fluids in the pipelines and piping systems . A check valve also knows as a non-return valve (NRV) or one-way valve because it permits the fluids to flow in only one direction.

Why do we need check valves?

These are simple solutions to potential problems. If the backflow is polluted, the backflow can cause problems and thus contaminate the upstream medium. For example, sewer lines have check valves to prevent debris from leaving and re-entering the system.

What type of valves do pumps use?

Certain types of pumps often use non-return valves. Diaphragm pumps and Piston pumps (such as chromatography pumps and metering pumps) often use outlet and inlet ball check valves. Check valve usually looks like a small cylinder and is connected to the pump heads on the outlet and inlet lines. Many pumps like mechanisms are used to move large amounts of fluid around the use of check valves (like ball check valves). The ejector or feed water pump that supplies water to the steam boiler is equipped with these valves to prevent backflow.

What is a one way valve?

These check valve types permit fluid to flow through a soft pipe with a flat shape that has a natural end. This flat shape resembles a duck building, hence the name of the one-way valve type. The fluid opens the flat edge of the duck house and lets the liquid through. As the inlet pressure releases, the edge of the duck house will return to a balanced state, and flow will block.

What is butterfly valve?

The butterfly valve or wafer check valve can use interchangeably. These types of check valve have a wafer or butterfly-type disk on hinges and springs. Both sides of the valve open as the inlet pressure exceed the cracking pressure. But as this inlet or suction pressure drops or backflow occurs, the hinge spring (or backpressure) shuts the valve disk and effectively seals it. The butterfly valve permits the medium to flow directly with minor blockage.

What is non return valve?

This non-return valve consists of a guide disk that lifts from the valve seat so that the fluid can flow. These valves need cracking pressure to overawed the gravity and springs and a guide to keep the disk in a vertical direction to be repositioned with proper sealing and alignment.

What happens when the upstream pressure is below the opening/cracking pressure?

If the upstream pressure becomes below the opening/cracking pressure or there is backpressure (the flow tries to move from the exit to the inlet), the foot valve closes. The closing mechanism can be modified depending on the design of the check valve. In simple words, the backward pressure pushes the diaphragm, the ball, the gate, or the valve disk against the opening and seal it. According to the design, the closing process can be supported by gravity or springs.

Why do we need a check valve?

Check valves on building drains are installed to prevent sewage backups into buildings. Check valves are also installed on drain piping such as on some sewer lines (where sewer backups are likely) and on sump pumps discussed

Why do we use check valves in well water systems?

On private well water systems we still make use of check valves and backflow preventers, principally to prevent loss of well pump prime and to prevent the back-flow of water out of the pressure tank into the well when the pump is not running.

What is a check valve on a sump pump?

Check valves on sump pumps: Check valves are used in other plumbing applications as well, such as on sump pump drain lines to prevent back-flow of water from the sump pump exit piping into the sump pit when the sump pump turns off. See SUMP PUMPS GUIDE.

What is a spring loaded check valve?

Spring loaded check valves close quickly, prevent water hammer, and protect the pump or impeller assembly from back-flowing; most importantly a properly functioning check valve prevents loss of prime in the well piping system.

What is a backflow preventer?

A "backflow preventer" is a check valve installed on potable water supply piping to prevent possible contamination of the water supply system by backflowing but contaminated water from the building into the outside public water supply mains.

What does "short cycling" mean on a well pump?

Note: well pump "short cycling" or rapidly turning on and off increases check valve wear and so shortens their life. See our article on well pump short cycling. And variable speed pumping systems (Franklin Sub Drive/Mono-Drive) that cycle the pump on and off very rapidly are still harder on both the pump and the check valve.

Where should a check valve be installed on a submersible pump?

On a submersible well pump installation, if your well water pump does not have a built-in check valve [many submersible pumps do have a check valve], a line check valve should be installed in the discharge pipe within 25 feet of the pump and below the drawdown level of the water inside the well.

Overview

Technical terminology

Types of check valves

Applications

History

See also

External links