A check-valve is an amazing little device that lets a liquid or a gas flow one way only.
We'll need some to make a low cost water pump, but buying them can be a little pricy. So
in this project we'll be making our own, out of common materials, and for less than
a dollar.
For this project, I'm using a 3/4" male PVC slip adaptor, 3/4" tubing, a 3/4" plastic
ball, and an O-ring. I chose this adaptor because there's a little ledge on the inside
where the O-ring can sit. And it should look like this. The ball needs to be large enough
that it won't push through the throat, but small enough that it doesn't touch the sides.
Attaching the tube at this point won't really do any good because the ball will roll right
out. We need a way to secure it in position, so let's make a mark on our tube 5/8" from
the bottom and use a 1/16" bit to drill a small hole in the tube, continuing right on
through the other side. Now you'll need a strong piece of metal, like a nail or a thick
paperclip. I'm using one of these brad nails that go to my nail gun. Whatever you use,
it needs to be strong, and long enough to push all the way through the tube. The ends
of the nail will need to be flush with the sides of the pipe, so we can go ahead and
clip the end with the nail head on it, and now we've got ourselves a retaining bar that's
perfectly flush on both sides. The next step is to prime our connections and place the
O-ring into place inside the adaptor. Now let's drop in the ball and double check that
everything is seated properly. PVC cement is added to the pipe, making sure it covers
the holes where the nail is set. Then the pipe is pushed down to the point where the
holes dip just below the rim of the adaptor so that when the glue sets, this connection
will be completely air-tight. You can build this valve into any length of PVC pipe you
want, but I'm using this 1-1/2" piece because it's just long enough to accept another adaptor.
When it's glued and pushed together, it makes a nice little compact unit, with only a slight
gap separating the two ends. I took
the opportunity to make 4 of these valves and a visual inspection on the inside shows
that the ball and O-ring are still seated properly in place, and the retention bar keeps
it all together. To finish up, I gave these a quick paint job, and wrapped one end with
a bit of electrical tape to indicate the direction of flow, similar to the marking you'd find
on an electrical diode. A fluid can pass freely in one direction, but if the valve is turned
around, the pressure closes the valve and the fluid is blocked. The quality of the seal
can be tested by dipping the pressurized valve in a bowl of water. This will show us if any
air is escaping at all. The pressure can be released though, by pushing up on the inside
of the valve to break the seal between the ball and the O-ring. I tried using a couple
of these valves to make a hand pump, which you'll be able to find in another project.
It'll compress air, and move water at over 5 gallons per minute. You can even create
enough suction to form a makeshift vacuum pump. The threaded ends of the valves make
them easy to connect, replace or rearrange whenever needed. Just for curiosity, let's
pressure-test the valve by hooking it up to an air compressor using this pneumatic adaptor
that we made in the Rocket Rifle project. The system's set at 20PSI, and you can see
the valve close off and prevent any air from leaking. When I crank it up to 50PSI, the
pressure difference is a little more obvious by the compression of the O-ring, and I'm really impressed at
how well it works. As an alternative, I found that a rubber bouncy ball could replace the
entire valve mechanism for low pressure applications. Since the ball is rubber, you don't need an
O-ring to seal the port. To make it work, just grab a sharp knife and a cutting board,
and begin cutting the top third of the ball very slowly, until you've sliced right through
it. Now re-insert the ball with the round side facing down, and simply slide the tube
in overtop. Amazingly it's that easy, and my kids use it for blowing up balloons. Well
there's how to make some useful pressure rated check-valves for as little as 35¢. If you
like this project, perhaps you'll like some of my others. Check them out at www.thekingofrandom.com