I got the fittings I ordered and tried them out. They work very nicely and seem to be just the thing for this particular application. Here's a picture of the construction so far:
There's a bit of illusion here. The pipe and elbows are 1/4 inch, not huge like the picture seems to show. I switched to 3/16 inch barbed Kynar check valves too. Yes, I know I said they would restrict flow, and they do, however they pass enough water to work OK. I'll just have to run the pump a little longer. I have the compression fittings in place and they seal it real nice.
Be sure to put Teflon tape on all the joints. If you don't the plastic binds up and causes leaks; the Teflon does a great job of lubricating the fittings and sealing any leaks. I've already tested the Teflon for acid resistance back when I was working on the level indicator. There are a few things to note about putting this together though. As I mentioned before, the tubing is a tiny bit large to work with the fittings without doing something. After destroying a couple of feet of tubing trying to get it to work, I came up with a simple procedure. First, take the compression fitting apart:
The main body piece has a tapered insert that you should bottom the tubing into, but it won't fit so, break out the heat gun and soften the plastic.
Once the plastic is soft, shove it into the body fitting all the way to the bottom.
Let it cool and take the body section off and put the other pieces in place.
Notice the positions of the pieces; this is important. The one nearest the nut is compressed by the nut and grabs the tubing, the other one slides into the body completing the seal. So, now just shove the tubing into the body, work the compression nut down and thread it on.
This method has given me an easy to make connection that doesn't leak. I did this for both sides of the pump and will have to do it for the foot valve and injection valve when I install it.
Now, the only thing holding me up is a set of clamps. The 3/16 inch check valves need a smaller clamp than I have and I have to wait for them to come in. The seal on the barb fitting is quite good, but there's a lot of vibration and temperature extremes to deal with and I want clamps on the fittings. The problem is that the clamps are acetate, and they will react to the HCl that will be flowing. That's OK for everything except the foot valve, fortunately, that's on the suction side and under the level of the HCl, so if it leaks some, I don't care.
I hope that I can get this installed and go back to electronic projects for a while soon. I want a couple of timers and a way of telling the garage door is closed from way far away, but I've been stuck with other things for months now.