So, let’s say you have a project that needs something to flow out but not in. It could be in a plumbing system, to keep contaminated water from seeping back into the clean water supply. Maybe you need to keep gasses from mixing in your welding torch. Or you are adding CO2 to your latest home brewing creation and you don’t want beer backing up in your lines.
A check valve, also known as a non-return valve, could be the solution. Check valves arrest backflow by placing a barrier to normal flow that can only be opened by pressure in one direction. There are several ways that this can be achieved, but two primary designs are swing check and in-line spring check.
We’ll talk about the swing check in this post and follow up with the in-line spring check in the next.
A swing check design is simplicity in itself in most cases, a swinging - usually disc-shaped - flap is hinged vertically inside the pipe. Gravity ensures that the flap hangs flush with the valve seat. Fluids come in from one end, press against the gate and push it into the open position. That allows flow through the valve so long as the pressure exists and pushes in that direction.A cutaway diagram of a swing check valve shows the flap which closes off a pipe from backflow.
If the pressure stops, the flap falls back into place and closes off the valve. If pressure builds from the other direction, the gate is pressed solidly against the inflow opening, blocking fluids from entering the pipe and contaminating the source.
Having trouble seeing it? Think of a doggie door that only let’s Fido out. While that might not be ideal for most pet lovers, consider all the times your pooch has rolled in something unpleasant and come back in to lie on your bed. Bet you wish you’d installed a swing check valve-style doggie door to keep those contaminants out then … until you got home with some canine-friendly shampoo, of course.
Swing check valves are good for backflow prevention in many cases and are useful because they take very little pressure to operate – or “crack” - into the open position. The DuraChoice Brand swing checks carried by DirectMaterial.com need only a half-pound of pressure to open and come in brass or stainless steel.
One downside with all swing check valves, though, is that they must be installed horizontally. Because they need gravity to force the flap closed, they cannot be installed vertically.
Next up, we talk about the swing check’s more pressure-resistant cousin, the in-line spring check valve, which can be installed either horizontally or vertically.