Saturday, August 4, 2007

Strainers

Prior to the testing in the last video, all of our tests had been done using potable water. That's with no mud, and no sand or rocks. It occurred to us that when we started pumping pond water, we would need a strainer of some sort to keep such material out of the pump. Our check valves were designed so they would probably tolerate particles smaller than 1/8", allowing them to pass through. One of the first things we did with the new valves was to allow the pump to ingest a lot of sand. As expected, it clogged things up and required the disassembly of the pump to clear out the sand. What this taught us was that our Delrin ball check valves were as robust as we could expect, as they experienced no damage for the abuse they received, and that as expected, particles of sand or rock slightly larger than 1/8 " would jam the ball in the valve open. It also taught us that the green suction plumbing we were using had to be removed with a hacksaw. Not good. Plumbing changes are underway as I write.

The photo shows two of our homemade strainers. The thing at the bottom was an idea we abandoned. It's a lateral for a swimming pool sand filter. It most likely would have done a good job, but there aren't just lots of pool supply stores where this pump is going, and they're expensive.

The other two strainers are just pieces of PVC pipe. One was drilled with 1/8" holes and the other slotted with a bandsaw, although it could have been done with a hacksaw, or a carpenters coping saw just as well. Both strainers were tried, and both worked. The second photo shows what happened to the strainer with holes after a few minutes of pumping. The same particles that would have stopped the check valves clogged the strainer. What we finished with was a slotted strainer about twice as long as long as shown in the photo, to provide more slots and accordingly reduce restriction to flow. We pumped for two hours, with no appreciable clogging. There will be more on our test results with the next post, and another video.

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