GET CHECK VALVE WIKI

Valve Wiki

A valve is a device or natural object that regulates, directs, or controls the flow of a fluid (gases, liquids, fluidized solids, or slurries) by opening, closing, or partially obstructing various passageways. Valves are technically fittings but are usually discussed as a separate category. In an open valve, fluid flows in a direction from higher pressure to lower pressure.

The simplest, and very ancient, valve is simply a freely hinged flap that swings down to obstruct fluid (gas or liquid) flow in one direction but is pushed up by the flow itself when the flow is moving in the opposite direction. This is called a check valve, as it prevents or “checks” the flow in one direction. Modern control valves may regulate pressure or flow downstream and operate on sophisticated automation systems. (sources from Wikipedia)

Check Valve Wiki

A check valve is a type of valve that normally allows fluid (liquid or gas) to flow through it in one direction, but not the opposite 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, many check valves are very small, simple, and/or cheap. 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, and some alloy check valves are made of exotic materials, such as nickel-copper alloys or titanium.

Type of Check 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 is more or less conically-tapered to guide the ball into the seat and form a positive seal when stopping reverse flow.

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 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, which permits flow. 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. True union ball check valves allow for easy removal and replacement of balls, eliminating the need to buy a new valve.

Diaphragm Check Valve

A diaphragm check valve uses a flexing rubber diaphragm positioned to create a normally-closed valve. Pressure on the upstream side must be greater than the pressure on the downstream side by a certain amount, known as the pressure differential, for the check valve to open allowing flow. Once positive pressure stops, the diaphragm automatically flexes back to its original closed position.

Swing Check Valve

Swing check valves are called ‘tilting-disc’ or ‘flapper’ check valves. They have a disc on a hinge (or trunnion) that swings open with an inlet pressure. The disc swings shut as the inlet pressure decreases or if there is backflow. If there is no spring to assist in closing, mounting orientation is important to consider to ensure that the disc swings shut with gravity. A dual disk or double door check valve has a central disk that is split into two semicircular doors that function independently hinged on a central pivot point. Figure 7 shows an example of a swing check valve. Read our article on swing check valves for more information.

Stop Check Valve

A stop-check valve is a check valve with override control to stop flow regardless of flow direction or pressure. In addition to closing in response to backflow or insufficient forward pressure, it can also be deliberately shut by an external mechanism, thereby preventing any flow regardless of forward pressure.

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 the 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.

Spring-loaded in-line Check Valve

In-line spring-loaded check valves are common, easy to understand, and have a simple design. Figure 2 shows a spring-loaded in-line check valve in the open and closed positions. The arrows indicate flow direction. When flow enters the input port of the valve, it should have enough pressure (force) to overcome the cracking pressure and the spring force. The pressure pushes the disc, opening the orifice and allowing flow to move through the valve. When the input pressure is no longer high enough or there is enough back pressure, the back pressure and spring push the disc against the orifice and seal the valve shut. The spring, along with the short travel distance for the disc, allows for a quick reaction time for closing. This valve design also prevents pressure surges in the line, preventing water hammering.

Duckbill Valve

A duckbill valve is a check valve in which flow proceeds through a soft tube that protrudes into the downstream side. Back pressure collapses this tube, cutting off flow.

Multiple Check Valve

Multiple check valves can be connected in series. For example, a double-check valve is often used as a backflow prevention device to keep potentially contaminated water from siphoning back into municipal water supply lines. There are also double ball check valves in which there are two ball or seat combinations sequentially in the same body to ensure positive leak-tight shutoff when blocking reverse flow; and piston check valves, wafer check valves, and ball-and-cone check valves.

Flap Valve Wiki

A flap valve is a type of non-return device for water or sewerage. The purpose of a flap valve is to ensure water can pass through the valve in one direction only. Flap valves operate by water flowing through a pipe or culvert and pushing the swinging door open. When the water level on the downstream side of the flap valve is higher than in the pipe or culvert it presses the swinging, door shut and prevents the water from traveling back through the system.

A Flap Valve, in simple words, permits gas or fluid to flow in one direction while preventing backflow. A spring-loaded or weighted flap affixed to the opening of a pipe, tube, or duct accomplishes this function. Flap valves are commonly used as industrial equipment to direct flow in the desired direction. They can be opened manually or remotely, and they can be opened by the force of the flow. The purpose of a flap valve is to send water out of a flanged pipe while preventing debris such as sticks and leaves from flowing back in. The valve will open when direct pressure is applied to it, and it will close when that pressure is alleviated.