Duxburian wrote:@Drench: What is the ideal pipe ID for the grommets? As you know, PVC is made to very precise OD specifications, but the ID can vary wildly. This is why I have trouble seeing PVC as a good, consistent pump shaft material.
I've used rubber grommets as pump seals in both Riptide and Cloudburst, and both had slightly different IDs despite being nominally the same size (1/2 inch schedule 40 PVC). If I remember correctly, Riptide's ID is larger than Cloudburst's ID. But this doesn't really matter all that much, because you can squish the rubber grommets enough to make the seal thicker, if you need to.
What do I mean by squish them together? Well, the grommets are just about 5/8 inch in diameter just out of the package (when not subjected to any force). But when installed, the screw squishes them in the direction of the motion, which makes them expand radially. This radial expansion means that even large ID 1/2 inch schedule 40 pipes will still seal well. I remember having no trouble inserting the pump rod into Riptide, but I had more trouble with Cloudburst (which had slightly thicker pipe), so I just dialed in the screw a little to adjust the tightness and used a little more lubricant.
So, to be brief, I think this design works well despite the variations in pipe size.
The Drenchenator, also known as Lt. Col. Drench