Monday, March 19, 2012
I'm still working on the darn acid pump. I don't mess with this full time obviously, but I keep getting back to it. The latest is that I'm not entirely happy with the new fittings and setup. The tubing is 5/16 inch OD and 3/16 inch ID; this is an odd size, and of course, doesn't fit the 1/4 ID barb fittings. 3/16 inch barb fitting have too small a hole for fluid to pass easily and reduces the volume too much. It is possible to expand the tubing, but thick wall polyethylene tubing is tough to work with. I heated several little pieces of tubing and experimented until I could actually put one on the fitting, but it was a trial and error process. When I tried the pump out, it didn't leak, but the vibration worries me. Here is the setup as I tested it:
Notice the clamps I used to hold the tubing and the 3/8 inch MPT fittings? The Kynar check valves worked great and didn't have any back leakage at all. They have Viton diaphragms that shouldn't have any trouble at all with acid. They will wear out over time though so I'll have to replace them periodically.
My concern is that the vibration shakes the tubing and it could leak over time since it gets hard and soft as the temperature changes and could shake loose. Now, I'm looking at some compression fittings for plastic tubing. The problem is that most compression fittings are Nylon, which will dissolve, or have a metal insert, which will also dissolve. I found some compression fittings that should work and even have configurations that may work for me:
This one only comes in 1/4 inch MPT, so I need reducers and adapters to fit it to the pump and direct the tubing. I have an assortment of 1/4 inch MPT fittings, nipples, and elbows on their way to accomplish this. These compression fittings are very different from the ones on the pump originally; they compress from the outside and have a built-in compression ring. The tubing fits much farther inside as well, and they are supposed to handle quite a bit more pressure than I will be putting on them. Oh, did I mention that they are solid molded Kynar. That'll show that stupid acid who's boss.
I still have to use tubing barbs to connect the kynar check valves, but I'll address that problem (if necessary) when the plumbing parts arrive. Strange, I never even knew there was such a thing as 1/4 MPT fittings. I'm real familiar with 1/2 and 3/4 inch fittings from working with water and natural gas piping, but the thought of 3/8 inch and below never even occurred to me. Home Depot and Lowe's don't even pretend to have many of these items; certainly not in materials like Kynar or Viton. No wonder people don't try to do obscure projects like this.
Posted by dave at 10:49 AM