Friday, December 9, 2011

Acid Pump - New Pump Head Arrived

As I mentioned before, the acid pump fittings melted and the company was sending me a new pump head under warranty.  It came in and I got around to installing it, the day before yesterday.  Wasn't hard, and it seemed to work.  I took a look at the fittings and there are some serious shortcomings to the way they work.  Yes, I realize I'm not a mechanical or hydraulic engineer so my opinion is suspect.  But, there's some common sense things that should have been thought of here.

First, the materials they use simply shouldn't dissolve when they are used for purposes clearly spelled out in their flyers.  They specifically say it will handle concentrated HCl...the pump does, but the nuts that hold the hoses in place don't, they melt.  They say the self-priming height is 5 feet, it's about a foot, maybe a little more.  If the pump loses prime, you have to lift the bucket up to the height of the pump to get it to prime.  The darn thing has a serious tendency to leak.  The way the fittings screw into the pump head doesn't allow the O ring to compress well and great care has to be taken to make sure it seals.

But the thing that ruined the previous set of fittings is the simple nipple that holds the tubing to the pump head. This is what it looks like.
There are several of these, one each for suction, discharge and injection, and each of them have the same shortcoming.  I took this drawing directly from their installation manual:
Notice where the tubing is pressed onto the fitting?  This is only about 3/8 inch long and has no barbs; it relies on the compression nut to hold it in place and the compression nut will bottom out on the threads so you can't actually compress it enough.  Any deterioration to the tubing such as aging for a couple of months under pressure and it will start to leak.  So, between the bottom of the fitting not compressing an O ring that should seal it and the compression nut not being tight enough on the tubing, it will fail over time.  Also, notice in the picture above that the nut is a slightly different color?  The nut is obviously made from a different material than the rest of the fitting.  Shouldn't the nut have the same chemical resistance as the rest of the assembly??  Some engineer somewhere didn't think so.  There is a different compression nut available:
It's a different color and probably a different material.  This one might work, but they sell it in lots of a hundred.  HUNDRED??  What the heck would anyone need a hundred of these things for?  Do they fail often enough that one would need a hundred on the shelf as replacements?  Maybe, just maybe I answered my own question......

I spent a bunch of money on this device and I don't intend to just give up on it.  It's likely that I can find valves that will work and don't have the shortcomings I detailed above, or maybe a little redneck modification can over come the problems.  For example, if I wrapped the threads of the fittings with teflon tape so the threads sealed, the O ring problem might go away since it would serve only as a backup to the threads being sealed.  Similarly, I could wrap the tubing with teflon tape to increase the pressure from the compression nut to help overcome the sealing problem.  Maybe drill out the nipple where the tubing slides on and thread in a barbed fitting for the tubing?

I haven't given up yet.

No comments:

Post a Comment