Check Valves

IQS Newsroom Articles on Check Valves

About Check Valves and Check Valve Manufacturers Including: Ball Check Valve, Brass Check Valve, Double Check Valves, Lift Check Valve, Miniature Check Valves, Non Return Valve, Plastic Check Valves, PVC Check Valve, Relief Valves, Spring Check Valve, Swing Check Valve & Wafer Check Valve.

Check valves are self-activating relief valves that operate entirely by reaction to the flow and pressure generated by the process streams in which they are installed. Also known as one-way directional or non return valves, these devices are designed to allow fluid, air or gases to flow in only one direction and eliminate backflow. Large and miniature check valves are employed in a number of industrial, commercial and domestic applications where they are responsible for the safe and consistent downstream flow of a number of materials including water, oxygen, fuel, acids, bases, sludge, slurry and even hazardous waste. Metal and plastic check valves may be used in variable applications. It is important that the material construction be compatible with the chemical composition of the process stream. PVC check valves and brass check valves are popular as they provide durable devices that can handle both chemical corrosion and constant wear. Selecting the proper valve configuration also helps to eliminate unnecessary wear and improve product longevity. Ball check valves, lift check valves, swing check valves and wafer check valves all allow the continuous downstream flow of materials while blocking upstream contamination. When the differential pressure across the valve is high, spring check valves are used to prevent valve clapping and overflow due to heightened downstream flow as well as protect against strong upstream surges such as water hammers. Double check valves, which use multiple valves in conjunction with one another, may also be employed to reduce wear and further protect against backflow which may otherwise result in pressure surges, cross-contamination and even flooding.

Check valves are increasingly popular in many applications for their simple design and ease of use. The mechanics are fairly simple. As aforementioned, check valve operations are determined completely by the process flow, meaning no additional actuating mechanisms are necessary. In general, the valve appears as a cylindrical device attached to the pump head on the inlet and outlet lines. Open in both ends, the working apparatus cross-cuts the housing dividing it into an upstream and downstream portion. The seat extends from the walls of the cylinder but has an opening suitable to passing the process stream. A ball, cone, disc or other oversized device rests against the seat on the downstream side of the check valve. While this may move, it is limited so as not to be swept downstream. When the stream moves in the pre-determined direction at the necessary pressure, the plug is dislodged from the seat and fluid or gas is permitted to pass through the resulting gap. As the pressure drops, the stopper returns to the seat to prevent backflow. Gravity or a spring loaded mechanism are commonly responsible for this return motion, though in some instances the increased pressure on the downstream side of the valve is enough to move the device back into place. The closing of the valve prevents downstream materials from mixing with upstream materials even under increased pressure. The specific stopper used is variable depending upon the type of check valve installed. As the name suggests, ball check valves use a ball. Lift check valves utilize a cone or disc attached to a rod like guide which ensures it will return to the proper place on the seat. Swing and wafer valves use one or more discs to seal the gap in the valve seat.

While the general design and function of the check valve is relatively simple, there are a number of important considerations which must be taken into account in order to ensure that materials can flow through the valve and that backflow will be adequately prevented. Check valves come in a range of sizes. The most important consideration regarding the size is the diameter of the seat and stopping device, which may be less than an inch or up to several feet across. Properly sized check valves are easily installed in pre-existing flow lines, using the dimensions of the pipe or tubing to determine the necessary size. The valve size will also affect the pressure rating or cracking pressure of the valve. This is the minimum pressure at which the valve will operate, or open. If the valve is too large or bulky, the pressure created by the process stream will not be able to open it, even when the opposing pressure is exceeded. Undersized apparatus will allow a continuous flow and never close. Such malfunctions could cause serious mechanical failures resulting in damaged equipment, wasted materials and potentially hazardous cross-contamination. The materials of construction also impact the effectiveness of check valves. If incompatible materials are used, they will wear, erode or contaminate the process stream. As a number of plastics, metals and even synthetics may be used, compatibility is always attainable no matter the gas or fluid being transferred. Common materials include PVC and brass as previously mentioned as well as ductile iron, copper, polyethylene, polypropylene, aluminum, steel, stainless steel and rubber. Further factors to consider include media temperature and valve flow coefficient.

Each of the aforementioned considerations, as well as the specific type of check valve employed depends largely upon the intended use for that valve. Virtually every plumbing or fluid transfer application imaginable, be it industrial, commercial or domestic, will employ check valves. In fact, check valves are an essential part of every day life. They are used in water heaters, indoor plumbing, faucets and dishwashers as well as more advanced equipment such as metering pumps, tankers, flowmeters, boilers, steam traps and industrial mixers and blenders. Sewage, water treatment, medical, chemical processing, power generation, pharmaceutical, chromatography, agriculture, hydropower, petrochemical and food and beverage processing industries utilize check valves in the everyday operations of their facilities for effective backflow prevention. Because they need not be supervised to function and prevent product malfunction, check valves are not only desirable, but often required by law to ensure the safety of water, gas and pressure applications.

Check Valves and Check Valve Manufacturers Images Provided by Check-All Valve

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Types of Check Valves

• Ball check valves are valves where liquids can flow only one way. The pressure from the liquid forces the ball to move, when the pressure from the fluid stops the ball also stops and the valve closes.
• Brass check valves are pipe fittings made of alloyed copper and zinc that are designed to regulate the flow of a process stream and protect against back pressure or backflow.
• Clapper valves are a type of check valve used in firefighting. This valve has a hinged gate (often with a spring pulling it shut) that will only remain open in the outflowing direction.
  
• Double check valves consist of at least two independently acting check-valves. They are typically used in liquid services.  
  
• Foot valves are often used in conjunction with a pump. The valve aids in pumping water and helps prevent backflow. 
  
• Hydraulic check valves prevent backflow in hydraulic systems, typically using a ball or a poppet.   
  
• Lift check valves has a disc, sometimes called a lift, that can be lifted up off its seat by higher pressure of inlet or upstream flow. A guide keeps motion of the disc on a vertical line, so the valve can later reseat properly.
  
• Miniature check valves are designed for precision fluid or gas flow regulation in small applications where unidirectional flow is needed. These micro valves operate with the same components as larger check valves, but with each element scaled down considerably. 
• Non return valves are another name for check valves, or valves that regulate the directionality of gas or liquid process streams. Also known as one-way directional valves, these devices are employed in virtually every industrial, commercial and even domestic application that involves the unidirectional flow of materials.
• Plastic check valves are unidirectional flow control devices made out of organic, synthetic or processed polymers.
  
• Pneumatic check valves allow fluids to flow in one or two ways. When the fluid is allowed to flow more than one way it is often metered.  
  
• PVC check valves are unidirectional flow regulators made of a particularly versatile thermoplastic resin and easily suited to the specific needs of industrial, commercial and even domestic check valve applications. An acronym for polyvinyl chloride, PVC is a highly diverse polymer that can be formulated to suit a number of check valve applications.
• Relief valves relieve excess and potentially dangerous pressure from piping systems or closed-top vessels and are normally closed until the set pressure is reached. 
  
• Sanitary check valves are used when the fluids contained in the pipes need to remain germ free. These check valves are often used for medical, food, or dairy purposes.  
  
• Silent check valves have a spring-operated return mechanism. They eliminate the shock of sudden reversal of flow, making them a favorite for use in clear liquid systems.
  
• Spring check valves implement coiled metal components in order to increase the amount of pressure needed to open the valve as well as help maintain closure even in the presence of strong reverse flow surges.
• Stop check valves are a type of check valve with override control to stop flow regardless of flow direction or pressure. When the valve is open, it acts as a check valve, but the valve can be deliberately shut to stop flow. 
  
• Swing check valves use outside levers to slow down the flow of materials through a pipe. The lever pulls the disk into the flow which causes the flow to stop more quickly.  
  
• Wafer check valves are often used for liquid services. The check valve is made of two half-circle disks hinged together. With positive flow, the two disks fold together to allow materials to flow through the pipe. With reverse flow, they retract to a full circle to restrict flow.

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Check Valves Terms Actuator - A part of a regulating check valve that converts various forms of energy (electrical, fluid, etc.) into mechanical motion to open or shut the check valve seats.   Backflow - A system's reversal of normal flow resulting from an increase in the downstream pressure exceeding that of the supply pressure.   Back Pressure -The pressure that is the result of a restriction of the main flow, caused by gravity, pumps, or restrictions on the pipe; measured in inches H20 or PSI.   Elastomer - A material often used by top check valve manufacturers, in the production of custom check valves which can be stretched or distorted but will return to its original shape.   Extended Bonnet - Device used when the material running through a pipe or a valve is at high or low temperatures. This device helps prevent damage to the sealing materials within check valves.   Fluid Power -Power that is used to provide motion and force to mechanisms by applying, generating, and controlling pumped or compressed liquids or gases; this term also encompasses hydraulics and pneumatics.   Penstock Valve - A gate valve often found in waste water treatment plants. It is used to contain fluids within check valves and custom check valves.   Pilot Valve - A small valve which operates a larger check valve with very little power necessary for use; utilized when the system requires the no-return characteristics of check valves for only a portion of the cycle.   Pneumatic - Operated or pressurized by air or other gases.   Pneumatic Actuator - A device that utilizes pneumatic energy to regulate or open/close the check valve. A spring that is used solely to open many custom check valves, will normally be fitted inside a valve which allows the valve to return to the closed position.   Poppet - A valve that moves up to or from its seat perpendicularly within check valves.   Positioner - Makes certain the closing device of check valves stays in the correct position.   Pressure Differential - Pressure difference in check valves found between the inlet and the outlet.   Pressure Spike - A quick pressure rise common to many custom check valves.   PSI (Pounds Per Square Inch) - A unit of pressure; equivalent to the metric unit of Kilonewtons per square centimeter.   Tank Valves - Check valves that are able to be inserted into the bottom of tanks.   Valve Seats - A stationary part of custom check valves which restrict fluid or gas flow when it comes in contact with the movable portion of many custom check valves.

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