Thursday, March 29, 2012

Acid Pump - Running Again

Well, it's installed.  I got the clamps in and tried them out.  Everything was fine and I put it all together and installed it.  Naturally, I had to build a new enclosure for it and there were a few problems installing it, but it's working now.  Here's the device on the fence:

I made the enclosure from some plywood I had in the garage and painted it with a thick layer of latex paint to help keep the wood from being attacked.  I may tie down the cables and tubing after it runs a while.  There's no  bottom on it because I wanted plenty of ventilation for later in the summer, also it will help dry things out if something does leak somwhere.  Here's how I hooked it into the pool plumbing:

It's just too bad I couldn't find check valve in Kynar that had threaded fittings; that would make it a really clean installation.  Everything works and doesn't leak; now I just have to watch it a few days before I trust it.

When I pulled the foot valve out of the acid to put in a new check valve, the nut that held the tubing had completely dissolved.  The tubing was still attached, but the nut was just gone.  This validated my diagnosis that the nuts were losing grip because they were dissolving in the acid.  This is really irritating because the pump is advertised specifically for chemical dosing.  It seems that the entire problem set I've been trying to overcome would never have happened if they had used high density polyethylene nuts to hold it together.  Since the nuts are custom to their fittings, they can't be second sourced to eliminate the problem either.

Here's the entire installation in place.  To review, the remote control timer that is on my XBee network is on the left in the gray box and the pump is in the new white box; they are both attached to the fence around my pool equipment.

Now I hope I don't have to mess with it for months except refilling the tank.

Update:  I listed the parts and their numbers at the end of my general write up on the injection system here.

Saturday, March 24, 2012

Acid Pump - Getting There Slowly

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.

Monday, March 19, 2012

Acid Pump - Continuing Drama

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.

Monday, March 5, 2012

Acid Pump - Replacement Arrived

I got my replacement acid pump a couple of days ago and just now got to testing my ideas for valves and fittings.  I'm trying these:


These are 3/8" NPT x 1/4 HB connectors and thread into the pump head just fine once I removed the valves they shipped with it.  I went with tubing connectors for two reasons, these have really long barbs and should seal well, and I couldn't find Kynar valves in anything except tubing configuration.  The Kynar valves look like this:

Notice how long the barb piece is?  That should stop any leaks if they don't dissolve in the acid like the other fittings.

I wrapped the pipe fittings with Teflon tape and screwed them into place.  The 1/4 tubing didn't want to go on the fittings so I got a heat gun and softened up the tubing.  I was able to slide it on just fine.  Now I've got the valves in place with some tubing pumping water around in a five gallon bucket.  I'll test this for a while before I put the pump in place and test it with acid.  I did notice though that the new check valves work really well.  They have no back leakage at all and open with very little pressure.  This should help a lot with my problems priming the pump.  The lines will have four of these valves in them to prevent backflow and loss of prime just like the original shipment so my cost is greatly reduced for maintenance.  These little valves cost less than a buck and a half while the original ones are more than thirty dollars (and don't work).

The pump will be in test mode for at least a day and then I have to get a couple of 1/4" elbow barb fittings because the tubing is so stiff I can't bend it like I want to.  I'm also going to get some tubing clamps like these:

I'll use these clamps around the barbs to make sure the tubing doesn't get warm and flex off during the summer heat.

Friday, March 2, 2012

Battery Charging Part 2 (Harbor Freight item 42292)

Part 1 of this project is here:

I've worked out my modifications to the little charger. Here is the schematic I ended up with:

I used two 100 ohm resistors to keep from hitting the supply rails on each end.  These aren't strictly necessary, but I had them handy and it seemed a little safer.  The diode on the output is to prevent the battery from discharging if the power is down for a long time; like I kicked the plug out of the wall.  It really isn't a 1N4001, it's some generic 1A 400V power supply diode that I had around.  The pot is 1000 ohm 25 turn and cost about a buck or so off ebay.  It allows me to set the voltage precisely.

Here is a picture of the way I hooked it up:

This will give me the float voltage that I want and won't discharge a battery if the power dies.  That makes it reasonable to put on a solar cell for things that don't have power near them.  A tractor parked out in the back somewhere, a quad setting next to a tent on a hunting trip; things like that.  Notice I got rid of the wires with the clamps on them.  I put a plug on the end and can now just plug it into the vehicle.  Improvements could be made like adding a volt meter to it to tell how it's doing and another light that says everything's OK, but those are for the future.  Now all I have to do is put it back in the case and label it with the voltage I set it to and let it do its job.