| Swing Check Valve Closed [1] |
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| Swing Check Valve Open [2] |
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Overview
A swing or butterfly check valve only permits flow in one direction. A swing check valve has a disc that is at the opening of the valve and is connected to a hinge at one end. When fluid comes into the valve, the disc is pushed into the opening of the valve as it rotates about the hinge. If the fluid were to move in the opposite direction, it would move the disc back into the opening of the valve and stop the flow [1].
A butterfly check valve has rod that goes through the center of the disc. The rod acts as an axle which the disc can turn about. The mechanism of opening and closing are the same as the swing check valve. The disc stays in the flow of the fluid even when the valve is open. This causes a pressure drop in the flow at all times [2].
Advantages & Disadvantages:
| Advantages [3] | Disadvantages [3] |
|---|---|
Imparts low resistance to flow | Can make noise as the disc hits the seat |
Usually less expensive | Cannot be installed upside down where the fluid flows from the top to the bottom (Figure 3) |
Bonnet cover can be removed for maintenance | Slamming the disc over time can cause damage |
Maintains pressure | Cannot be used with pulsating systems |
Considerations:
Fluid Type:
Either liquid or gas can be passed through the valves (Check manufacturer specifications)
Pressure:
Swing check valves open fully which allow for complete flow. Butterfly check valves have their disc in the valve which decreases flow pressure. One of the issues that may occur is a phenomenon known as water hammer. When a pipe has liquid flowing through it, the liquid has momentum. If there is a valve in the piping system which abruptly stops the flow of liquid, then the momentum of the liquid will hit the valve with a lot of force. In smaller pipes you may hear a bang as the valve closes. In larger systems, the water hammer can damage the system. One of the ways to prevent water hammer is to ensure that the valve is closed slowly. See the sizing section to determine what size of valve to get.
Sizing:
When selecting the right size of valve, there are a couple of measurements and calculations that need to be done. Firstly, the dimensions of the pipe must fit the dimensions of the valve. The housing of the valve will also protrude from the pipe diameter. Many manufacturers have the size of each part in the valve which can be useful if components of the valve simply need to be replaced. Pressure also plays a big role in the sizing of the valve. Calculations need to be be done so that the valve has the desired flow rate. This is done by calculating the flow coefficient and finding a corresponding valve for it.
Orientation:
Swing and butterfly check valves can be orientated horizontally and vertically. However, when orientated vertically, the flow must travel from the bottom of the valve to the top. If these check valves are placed in the wrong vertical orientation, gravity will hold the valve open. This is an issue because the valve will stay open even when there is no pressure from the fluid.
Maintenance:
Swing check valves can be maintained more easily because the bonnet cover can be taken off so that the components can be manipulated.
| Orientation Limitation [3] |
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| Flow Coefficient |
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