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A spring check valve is a valve that ensures unidirectional flow and prevents reverse flow. They have a single inlet and outlet and must have proper spring selection to perform effectively. On the side of a spring check valve, and all check valves, is an arrow that points in the flow direction. Spring loaded check valves are referred to as non-return or one way valves. The purpose of a spring check valve is to stop back flow using a spring and pressure placed on a disc to close the valve.
For a check valve to function properly, it has to have differential pressure with flow moving from high to low pressure. High pressure on the inlet side, or cracking pressure, allows the flow to move through the valve and overcome the strength of the spring in the valve.
Check valves, in general, are devices that allow any form of media to flow in one direction. The checking mechanism can be shaped like a ball, disc, piston, or poppet, a mushroom shaped head. When the pressure in a system begins to lower, slow, stop, or reverse, spring check valves prevent reverse flow as a method of protecting pumps, equipment, and machinery.
Swing check valves allow flow in one direction and automatically close when the cracking pressure decreases. They are a form of butterfly valve with a disc that covers the valve opening. The disc is attached to a hinge such that the disc can swing open or close when it is struck by the flow of the media. On the side of the valve body is an arrow that indicates the direction the flow must be as it enters and exits the valve.
The pressure level of the flow pushes the disc or door open, allowing the flow to pass through. When the flow moves in the wrong direction, the disc closes due to the force of the liquid or media pushing against it.
Swing check valves do not require external power. Fluid or media passes through them unobstructed by their presence. They are installed horizontally in pipelines but can be installed vertically as long as the flow is upward.
For a spring loaded check valve to function properly, it must have upstream pressure, known as cracking pressure, to keep it open. The amount of cracking pressure required varies depending on the valve type, its construction, spring characteristics, and its orientation in the pipe. The specifications for the cracking pressure are in pounds per square inch gauge (PSIG), pounds per square inch (PSI), or bars, the metric unit of pressure that equals 14.5 psi.
When the upstream pressure falls below the cracking pressure, back pressure becomes a factor, and the flow will attempt to move from the outlet on the valve to the inlet. As this happens, the valve automatically closes, and the flow stops.
With an axial flow silent check valve, the disc is held in place by a spring that centers the disc to allow smoother flow and immediate opening and closing. The spring and disc are in the center of the pipeline, and the flow passes around the disc. This is unlike the swing valve or other types of spring valves that pull the disc up out of the flow completely, leaving a fully open pipe.
The special design of axial flow silent check valves makes them more expensive than traditional spring check valves and swing check valves. Though they are more expensive, the return on investment is due to their longevity, which can be over three years before needing to be replaced.
The unique construction of an axial flow silent check valve can be seen below where the valve is open and the fluid is flowing through. Like spring check valves, axial check valves begin to close when the upstream pressure falls. As the pressure slowly decreases, the valve slowly closes.
A ball spring check valve uses a ball as its sealing seat located close to the inlet orifice. The sealing seat is conically tapered to guide the ball into it and create a positive seal. The ball is moved when the cracking pressure from the flow is greater than the spring that holds the ball, and the flow passes through. The spring moves the ball to close the inlet when the cracking pressure decreases.
In-line spring check valves are known as nozzle or silent check valves and have a stem and disc construction included with the spring. They open when the cracking pressure is greater than the force of the spring. The flow pushes the disc to allow the flow to pass through. When the inlet pressure reduces, the spring pushes the disc against the orifice of the inlet and closes the valve.
Lift spring check valves are placed in lines where globe valves are used as flow control valves. They can be used in horizontal or vertical lines and are recommended for use with steam, air, gas, water, and vapor lines. Flow enters below the seat of the valve and lifts the disc or ball off the seat. When the flow reverses or stops, the disc or ball is forced onto the seat by gravity and the backflow.
Some types of check valves allow the disc to slam shut in conditions where there is a reversal of fluid flow. Slamming is the result of the movement of the fluid in one direction, which stops or reverses quickly. Swing check valves slam as the fluid stops or reverses while spring check valves close before the process occurs, which prevents slamming.
A no-slam check valve has a spring applied against the fluid flow pressure. When the flow is strong, the spring is compressed and pulls back the disc, which is a very quiet and smooth process. The disc is moved back toward the seating surface when the flow slows or stops and before the flow reverses.
Spring loaded Y check valves have the same operating principle as in-line spring check valves. The difference is that the spring and disc are at an angle that forms the letter Y. The unique property of Y spring check valves is that they can be inspected and repaired without being removed from the pipeline.
As shown in the diagram, one leg of the Y has a removal seal above the spring and disc.
Swing check valves are the most common and useful of the various check valves. Though swing check valves and spring check valves have similar purposes, they function differently. They are grouped with all of the forms of check valves as an automatic method for stopping reverse flow.
The recommended use for swing check valves is in systems that use gate valves because of the low pressure drop across the valve. Two types of swing check valves are Y and straight body.
Composition disc swing check valves are used with gritty materials to reduce seat damage and wear on the disc. The disc of a composition disc swing check valve has a hard nonmetallic ring placed on it, which creates a tighter closure. Composition discs resist erosion and are resilient enough to close on solid particles without damaging the valve. They are quickly and easily repairable and require less power to seat.
Dual plate swing check valves are referred to as butterfly, folding, or split check valves. The dual plate swing valve disc is divided into two halves that open along its centerline with the upstream flow. When the flow reverses, the two halves close against the seal of the seat. Dual plate swing check valves are used where there is limited space since they are compact and lightweight.
Straight swing check valves have a circular disk that swings on a hinge pin. It is mounted horizontally. As the flow moves from upstream, its pressure opens the valve. When the pressure lowers, the valve closes. The seat on a swing check valve has a seat ring against which the door or disc rests when the valve is closed to create a tight uniform seal. The seating surface is at a slight angle to open at lower pressures, a positive seal, and avoid shock when closing.
Tilting disc swing check valves have a mix of design options that allows them to stay open when the flow is at a low velocity but to shut quickly to stop the downstream flow. They have a dome shaped disc that floats in the flow and is lifted off the seat to open the valve. As the flow weakens and slows, the disc rests on the seat to avoid backflow.
The structure of a Y swing check valve is similar to an in-line swing check valve with an additional opening that allows access to the valve without removing it from the flow line. One part of the Y shape allows the flow to pass through much like an in-line swing valve. When the disc swings upward as the flow moves upstream to downstream, it moves to the other part of the Y that has an opening allowing the valve to be repaired or checked.
The purpose of all check valves is to prevent reverse flow in a piping system. They are opened and activated by the flow of material through the system. The pressure of the media from the upstream to the downstream opens the valve while reversal closes it. Of the various types of check valves, swing check valves are the most commonly used and are the least expensive but most effective.
In the majority of cases, check valves are a safety measure that is designed to limit stress on a system and prevent slamming. The various types are engineered to meet the needs of a variety of applications and operations. Swing and spring check valves are widely used and are relied on for their dependability, ease of installation, and minimal need for maintenance.
Swing check valves are limited to horizontal flows or vertical upward flows due to the swing nature of their disc. Since they cannot support downward flow, there is a limit to the applications where they can be used. Regardless of this disadvantage, they can handle large flow capacity. Swing check valves offer low resistance to flow and flow pressure.
The parts of a swing check valve are built inside the valve body and do not penetrate the valve body. The solid single unit construction keeps a swing check valve sealed and prevents external leakage. The disc on a swing check valve has a degree of freedom in a range of 360 degrees with micro positioning compensation. The disc closes by gravity when there is no flow.
Though swing check valves are widely used in a variety of applications, they do not fit on all types of piping configurations.
A common complaint with swing check valves is the noise they make when they close with ones that have a metal on metal disc seat. When the valve closes, it produces a clanging or ringing sound.
Common uses for swing check valves are stoppers in toilets, firefighting equipment, and flood prevention in sewage systems.
The main benefit of swing check valves is their low cost, making them capable of fitting into the budget for any project.
A major concern with swing check valves is the water hammer, resulting from a pressure surge or high pressure shock caused when a fluid’s motion is forced to change direction or rapidly stop. It is heard as a banging or knocking sound in a piping system. Though a water hammer may seem harmless, the resulting force caused by the change in a fluid’s momentum creates pressure spikes that can exceed the designed pressure of a piping system.
Spring check valves have more versatility than swing check valves and can be used in a wide variety of applications, including horizontal and vertical ones. Since the spring holds the disc in place when there is a pressure drop, the flow can be vertical or horizontal. The pressure of the spring forces the disc to seal the opening.
Unlike swing check valves, spring check valves offer resistance to the flow and have to be opened by the pressure of the flow, which must be greater than the force of the spring.
The smooth motion of spring check valves makes them quieter. Instead of reacting to the flow, spring check valves close when there is a change in the pressure in the upstream flow. This means that they may close before any reverse in the flow, preventing water hammering.
Since spring check valves prevent water hammering, they are known as silent check valves. They radically reduce the noise in an application.
The versatility of spring check valves allows them to be installed in any type of piping configuration as long as the correct spring is chosen. In a situation where there is difficult spacing, dimensions, and a unique direction of the piping, a spring check valve can offer the perfect solution.
The types of pressure and materials that spring and swing check valves endure requires that they be made of materials capable of withstanding the demanding conditions and requirements of an application. The selection process for choosing materials to construct swing and spring check valves depends on the type of media, the pressure, the level of corrosion, and the temperature.
Included in the selection of materials is the amount of wear the valve will face and the cost of the final product, with certain resilient materials being more expensive than others.
The ready availability of iron and its low cost make it a perfect material for the manufacture of spring and swing check valves. It has good shock absorption but poor corrosion resistance.
Brass swing and spring check valves can withstand high pressure and temperatures. They are less expensive than steel and able to be shaped and configured to fit any type of check valve. Brass check valves can be connected to copper, brass, plastic, aluminum, and welded steel.
Bronze has many positive qualities that make it an excellent material for manufacturing check valves. It has high ductility to prevent cracking, corrosion resistance, and low cost.
Stainless steel is a commonly used material for manufacturing swing and spring check valves. Its many properties, including its resistance to corrosion and rust, make it an ideal metal for a wide variety of check valve applications.
Some of the characteristics of Monel include resistance to seawater and caustic solutions. It is hardened by cold working, has excellent tensile strength, and is weldable. Monel is resistant to corrosion and can be used in non-oxidizing chlorine solutions and marine applications.
Monel is the trademark for a set of nickel copper alloys with alloys including 400, 401, 404, K500, and R405. Included in Monel are traces of iron, manganese, carbon, and Sulphur.
The effects of molybdenum and niobium that are contained in the nickel chromium alloy give Inconel its exceptional strength and anti-fatigue properties. Some of the many features of Inconel include high tensile, creep, fracture strengths, and good welding properties, which make it easy to process. The difference between Inconel and Monel is the chromium in Inconel that replaces the copper in Monel.
The nickel and chromium combination in Inconel makes it possible for it to resist oxidation and high temperature corrosion.
The main attraction of PVC check valves is their lightweight, sturdiness, resilience, and abrasion resistance. As a plastic, PVC is not susceptible to corrosion, rust, or other damaging factors common to certain metals. The exceptional durability of PVC ensures its long life of usefulness. The popularity of PVC spring and swing check valves is due to how easy they are to install.
The flexibility and adaptability of PVC make it possible to manufacture spring and swing check valves in a wide range of sizes to fit the needs of many applications. A common use of PVC swing check valves is in pumping systems.
There are several ways that swing and spring check valves can be connected to a pipeline. The key factor for making a proper connection between the valve and the pipeline is to avoid leakage. There are several ways that connections can be made including flanged, threaded, welded, sweat, and press.
Each of the various connection forms ensure a tight fit between the swing or spring check valve and the piping system. Choosing the correct method of connection is essential for the successful use of the valves.
Threaded connections are the most basic form of valve to pipe connection methods and are used with small valves in low pressure systems. As the term threaded indicates, they screw onto a threaded pipe to form a tight and secure connection.
Flanged connections are the most robust and capable of connecting to any form of the piping system regardless of the pressure or valve size. They have two flanges, one at the inlet and one at the outlet, which are attached using bolts.
Press fittings are an alternative to welding and soldering. A hydraulic tool is used to press specially designed connectors to join the spring or swing valve to the pipeline. A sealing element, when pressed, creates an even, smooth, and reliable connection. They are also known as crimping and press connect joining.
The purpose of a welded connection is to form a tighter leak free joint connection. This connecting swing and spring valve method is more expensive but guarantees an extremely tight, secure, impenetrable, and exceptional linking of the valve and the pipeline. The use of welded connections is in areas where the absence of leakage is crucial, such as high pressure and temperature pipe lines.
For a sweat fitting, the swing or spring check valve openings are slightly larger than the pipe. They slip onto the pipe and have solder applied such that it seeps into the gap between the pipe and the valve fitting. This is normally performed with copper piping.
Check valves allow media to flow in one direction and have stopping mechanisms that come in a variety of shapes and designs. The purpose of a check valve is to protect equipment, assist in maintaining efficient manufacturing processes, and prevent reverse flow.
When there is a change in pressure in a pipe line, it causes flow reversal that can damage pumps and equipment. The change in pressure causes the check valve to close and block backflow and flow reversal.
Check valves can be designed using spring material with each type of material functioning differently in low pressure conditions. Pressure relief occurs when the poppet moves away from the valve seat as upstream pressure is applied that is greater than the force of the spring. As the poppet is lifted, the gas, fluid, or steam is allowed through the outlet. For a check valve to perform this function, it is essential that the maximum pressure and set pressure of the system are understood.
A vacuum breaker allows air into a pipe system to prevent stoppage of the flow. Check valves are placed at the top of piping of tanks to relieve pressure as a tank is emptied. They are also used when the elevation of a piping system occurs or when there are changes in temperature.
Check valves produce warning signs when they are failing such as vibrating as internal parts are lost. The most obvious sign of failure is reverse flow. All check valves create noise as they fail and break down, which is known as water hammer.
The main signs of failure are:
A check valve is a safety device designed to allow fluids and gases to flow in one direction. Under pressure, fluids enter the valve at the inlet and exit through the outlet. Uninterrupted flow continues until the pressure drops, or the pump is shut down...
A ball valve is a shut-off valve that allows or obstructs the flow of liquids and gases in a piping system by rotating the ball having a bore inside the valve for 90°. The ball is mounted against two seats and has a stem that connects it to the operating and control mechanism that rotates the ball...
A butterfly valve is a quarter-turn rotational motion device that utilizes a rotary disc to allow, obstruct, or control the flow of fluids in a piping system. It features a rotating disc that is situated on the passageway of the flowing media...
Diaphragm valves utilize a flexible diaphragm to obstruct, control, or isolate the flow of fluids. The diaphragm acts as the flow control element that flexes up or down to increase or decrease the fluid flow rate, respectively...
A PVC or polyvinyl chloride ball valve is a plastic on and off valve that has a rotary ball with a bore where turning the ball a quarter turn can stop the flow of a fluid. They are highly durable, cost effective and can be...