Types of Check Valves and Its Applications

A check valve, clack valve, non-return valve or one-way valve is a mechanical device, a valve, which normally allows fluid (liquid or gas) to flow through it in only one direction.

Check valves are two-port valves, meaning they have two openings in the body, one for fluid to enter and the other for fluid to leave. There are various types of check valves used in a wide variety of applications. Check valves are often part of common household items. Although they are available in a wide range of sizes and costs, check valves generally are very small, simple, and/or inexpensive. Check valves work automatically and most are not controlled by a person or any external control; accordingly, most do not have any valve handle or stem. 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 upstream pressure at which the valve will operate. Typically the check valve is designed for and can therefore be specified for a specific cracking pressure.

Types of check valves:

1. Swing Check valve

• Y-Pattern
• Straight- Through Pattern

2. Tilting disc check valve

3. Lift Check valve

4. Piston check valve

5. Spring loaded check valve

6. Foot check valve

7. Ball check valve

8. Butterfly Check Valve 

9. Ball Check Valve

SWING CHECK VALVE OR TILTING DISC CHECK VALVE

A Swing check valve or Tilting disc check valve is 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. The flapper valve in a flush-toilet mechanism is an example of this type of valve.

 

Tank pressure holding it closed is overcome by manual lift of the flapper. It then remains open until the tank drains and the flapper falls due to gravity. Another variation of this mechanism is the clapper valve, used in applications such firefighting and fire life safety systems. A hinged gate only remains open in the inflowing direction. The clapper valve often also has a spring that keeps the gate shut when there is no forward pressure.

• Y-Pattern Check Valves

   

Y-Pattern check valves are designed with an acess opening in line with the seat , which is integral with the body. This permits the disc to be rotated with a screw driver to regrind the seating surfaces without removing the valve from the line.

• Straight-Through Check Valves

  

Straight-Through check valves contain a disc that is hinged at the top. The disc seals against the seat which is integral with the body. This type of check valve usually has replaceable seat rings. The seating surface is placed at a slight angle to permit easier opening at lower pressures, more positive seating and less shock when closing under higher pressures.

LIFT-CHECK VALVE

  

A lift-check valve is a check valve in which the disc, sometimes called a lift, can be lifted up off its seat by higher pressure of inlet or upstream fluid to allow flow to the outlet or downstream side. A guide keeps motion of the disc on a vertical line, so the valve can later reseat properly. When the 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.

PISTON CHECK VALVE

  

Piston check valves are essentially lift check valves with a dashpot consisting of a piston and cylinder that provides a cushioning effect during operation. Because of the similarity in design to lift check valves, the flow characteristics through a piston check valve are essentially the same as through a lift check valve. Piston checks are used primarily in conjunction with globe and angle valves in piping systems experiencing very frequent changes in flow direction.

 

SPRING LOADED CHECK VALVE

  

Spring loaded check valves are actually a form of vertical lift check valves. The difference being that a spring is employed to effect the sealing. Advantage of spring actuation are : more rapid response to reversal of flow and the ability to be installed in any position i.e vertial or horizontal. Because of their rapid closing action they are more effective in controlling hydraullic shock in a piping system then some other types of check valves.

FOOT VALVES

  

A Foot valves are basically lift check valve which are used on the bottom of a suction line to maintain the pump’s prime. They may be of the lift check or ball check variety and are usually fitted with a strainer. The head of liquid above the valve holds the valve closed and keeps the suction pipe full. As suction is created when the pump starts up, the check valve opens and permits flow to the pump.

 

BUTTERFLY CHECK VALVES

  

Butterfly check valves have a seating arrangement similar to the seating arrangement of butterfly valves. Flow characteristics through these valves are like wise similar to the flow characteristics through butterfly valves. Consequently, butterfly check valves are uite frequently used in conjunction with butterfly valves.

 

BALL CHECK 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. In some ball check valves, the ball is spring-loaded to help keep it shut. For those designs without a spring, reverse flow is required to move the ball toward the seat and create a seal. The interior surface of the main seats of ball check valves are more or less conically-tapered to guide the ball into the seat and form a positive seal when stopping reverse flow.

Ball check valves are often very small, simple, and cheap. They are commonly used in liquid or gel minipump dispenser spigots, spray devices, some rubber bulbs for pumping air, etc., manual air pumps and some other pumps, and refillable dispensing syringes. Although the balls are most often made of metal, they can be made of other materials, or in some specialized cases out of artificial ruby. High pressure HPLC pumps (High Performance Liquid Chromatography pumps) and similar applications commonly use small inlet and outlet ball check valves with both balls and seats made of artificial ruby, for both hardness and chemical resistance. After prolonged use, such check valves can eventually wear out or the seat can develop a crack, requiring replacement. Therefore, such valves are made to be replaceable, sometimes placed in a small plastic body tightly-fitted inside a metal fitting which can withstand high pressure and which is screwed into the pump head.

There are similar check valves where the disc is not a ball, but some other shape, such as a poppet energized by a spring. Ball check valves should not be confused with ball valves, which is a different type of valve in which a ball acts as a controllable rotor to stop or direct flow.

Applications

PUMPS

The check valves on this steam locomotive are located under the small dome between the chimney and the main dome Check valves are often 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. The feed pumps or injectors which supply water to steam boilers are fitted with check valves to prevent back-flow.

INDUSTRIAL PROCESSES

Check valves are used in many fluid systems such as those in chemical and power plants, and in many other industrial processes. Check valves are also often used when multiple gases are mixed into one gas stream. 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.

DOMESTIC USES

Some types of irrigation sprinklers and drip irrigation emitters have small check valves built into them to keep the lines from draining when the system is shut off. Also used with most home made snowmakers. Check valves used in domestic heating systems to prevent vertical convection, especially in combination with solar thermal installations, also are called gravity brake. Rainwater harvesting systems that are plumbed into the main water supply of a utility provider may be required to have one or more check values fitted to prevent contamination of the primary supply by rainwater.