Sunday, July 8, 2007

Shop Made Check Valves

For some time we've been operating the pump with commercially manufactured check valves. They work great, but they're expensive. One of the first posts here was about an attempt to make check valves for an early pump using standard PVC fittings, and kid's toy glass marbles. These did in fact work, but clearly we had to make improvements. We're also trying to keep the cost of the pump as low as possible, and four of the most expensive parts are the check valves. The problem was finding a source of some sort of sphere that would serve to replace the glass marbles. There are lots of companies that make all sorts of spheres, balls and bearings out of every material you can imagine, from the mundane to the exotic. They're also very happy to sell them to you, in lots of thousands. We needed eight or ten for our purposes. Fortunately, we were able to locate Salem Specialty Ball Co. in Canton, Connecticut. They were very helpful, and very accomodating to sell us Delrin balls in sizes and quantities that met our requirements, for a reasonable price. Thank you, Salem Specialty Ball Co., and special thanks to Deloris. In case you're wondering, Delrin is an acetal resin similar to nylon. It is said to have excellent abrasion resistance, which is important if you're trying to pump water that may carry considerable quantities of sand and mud, does not absorb water (it shouldn't swell), and is advertised as an excellent choice for check valves. It's also cheap in quantities, which we hope to be buying, if one day this pump is well accepted. So there. As usual, I've provided a photo showing four check valves ready to be installed, and some of what's inside. You can click on the photo to enlarge it and get a better look at what I'm talking about.
The valves are made from one 1 1/4" coupler and two 1 1/4" x 3/4" flush reducers. A 7/8" delrin ball fits nicely in the throat of one of the reducers, and stops flow in that direction. When flow reverses, the ball would travel back to the other reducer, and stop flow in that direction too, except that it's stopped by what I'm going to call a spider, which is what those two complicated looking star shaped objects are in the front of the photo. One is made out of aluminum, which I didn't like too much. The other is made out of a piece of the PVC that both spiders are sitting on. The PVC came from a short section of PVC pipe that was slit down one side, and heated in a 300 degree oven for about five minutes. At that temperature, PVC is as pliable as putty, and can be flattened between two boards and held till it cools. After that, it can be cut, filed and drilled. The spiders look complicated to make, but they're not. You cut a square the right size, and drill a half inch hole in the center. Then you use a half round bastard file such as you see in the photo to file the half round recesses in the four sides of your PVC square. It's easy, and it only takes a few minutes. To the left you see a Delrin ball sitting on it's spider, inside a spacer cut from a piece of pipe to provide space in the valve for the ball to travel back and forth, and retain the spider. The second photo shows a cut away copy of the valve so readers can see how all this goes together inside. In quantities, the cost of this valve should be less than three dollars each. I'll let you know how they work as soon as I can get them installed in the pump.


Will said...

Hi. I am currently making one-way valves similar to duckbill valves for installation within the inlet and outlet pipes attached to a treadle pump, with the intention of testing them for frictional head losses. I would be interested to know how much the ball check valves here cost you per unit, and whether you have ever tried any similar testing (and if so what you found!). Many thanks and keep up the good work! Will

Will said...

Oops. Just saw that you have told us the cost! Still very much interested in the testing part though. Ta.

dive said...

nice post. ived been searching for articles about valves and actuators and your post really helps. thanks a lot for posting this.