Saturday, July 14, 2012
A few posts back I declared that I was done trying to make the Hanna Dosing Pump work. That was a fact, I've just had too many problems with this device and am totally tired of messing with it. I did some more research and turned up another alternative. Since there are only two types of pumps that are used for this kind of thing, peristaltic and diaphragm, and diaphragm had too many problems, I went for a peristaltic device. I found this one that somehow avoided my research the first time:
This is a Rola-Chem RC-25 and comes complete with everything in the picture. It can handle either chlorine or muriatic acid in the concentrations used for swimming pools. I normally try to use 30+ percent muriatic acid in my arrangements, so this thing should do the job just fine. Notice that they provide a brass fitting for the pool injection? They explain this by illustrating that the tubing should be pushed way down into the pipe so the water flow from the pool pump should dilute and carry it away from the fitting. This might just work since the flow rate of pool water is many gallons a minute and the pipe is two inches (usually) in diameter, the acid should dilute and move away quickly.
One of the major problems with the diaphragm pump was the force of the fluid motion. The diaphragm was solenoid operated and really shoved the fluid out hard. This wouldn't be a problem except for the operation of the various check valves: they were pounded by the movement of the water and that caused the diaphragms in the valves to wear very quickly. I discovered this by ripping apart several of the valves after they had failed. There were distinct wear marks on the internal diaphragms that would leak fluids both directions. This pump produces a relatively gentle flow that will build up to enough pressure to overcome the pools flow and its own check valve quite nicely.
This pump is made of plastic on the entire exterior. I couldn't find any place that would dissolve in the muratic, so it should stand up better than the last attempt. It comes with several feet of vinyl tubing to hook it up with. This led me to a discovery that I wish I had run across earlier: Vinyl is actually PVC. Yes, vinyl tubing (if it really is vinyl) should stand up nicely to muriatic acid. The resistance of PVC is lower than other materials, but the tubing will wear out due to exposure in about a year and need to be replaced anyway, so that shouldn't matter. Also, vinyl tubing is cheap and easy to get; just go the Home Depot, Lowes, or Ace and pick some up. The pump also uses standard size tubing and fittings that you can get most anywhere; just avoid nylon fittings, look for pvc or vinyl and you should be fine. The pump tube (the one inside) comes in two materials: Tygon and Norprene. Tygon is resistant to most chemicals and is used a lot in the food industry. Norprene is actually a form of Tygon that is specifically formulated to be UV resistant, flexible, and extremely durable. Rola-Chem recommends the black Norprene for muriatic and the clear Tygon for HCL. This is mostly because the acid is extremely corrosive and a little leak will mess things up over time; best to be safe.
So, I modified the box I had on the wall holding the Hanna pump and installed the Rola-Chem pump. This is after running the Rola-Chem into a bucket for a couple of weeks to be sure it worked and I understood how to use it. I discovered that the pump puts out about a cup (8 ounces, 225ml) every 8 minutes so I'll start out at 10 minutes and see how the acid level holds up in the pool, adjusting as necessary. I'm not using the timer control on the pump because I want to control the device from my House Controller; I just turned the switch to 'On' and hooked it up. It was relatively easy since I already had an injection point I installed for the previous pump and the bucket with level sensing has been working fine. I ran it for a couple of days on water to be sure it didn't leak and the timer controls were working correctly. Today, it was filled with acid and put into service. I was surprised how well it worked. This little device self primes in about a minute and the just rolls away moving the fluid through the tubes. Yes, I'll have to replace the pump tube twice a year and the other tubing every winter, but that's not a big deal at all. The internal tube costs about U$20 and the other tubing is less than that (remember, you can get it at Home Depot). It also needs lubrication periodically; I checked the label on the O-ring lube I use and it should work great. Just go out every month or so and put some in and it should be fine. I'll look at everything each time I clean the filters to be sure it's standing up to use. Here's a picture of the installation:
This pump was larger than the Hanna, so I had to enlarge the box (thank goodness for waterproof glue), but it should work nicely to shelter it from the hot sun and little rain that falls here. Notice the bottom is open? This worked well for the last several months. If it leaks, it doesn't set in the box and corrode things and it gets plenty of ventilation to keep things dry. There is the occasional spider though. Here is the injection point:
Notice the check valve? It's the gray thing that the clear vinyl tubing slips onto. This check valve was a pleasant surprise also. It is acid resistant and has a Hastelloy spring inside. Hastelloy is one of the few metals that is resistant to muriatic acid and hard to find in devices that normal people use. I chased down the manufacturer and it is available in several configurations from SMC, but they require a minimum U$100 order. I may pursue getting some of these to keep around if this works out. I didn't use the brass fitting that was supplied with the pump; I just don't trust brass and acid in proximity to each other. I've had too any bad things happen with that combination.
I haven't dressed the tubing or tied it down yet. I want to try it for a week or so first to see how things work out before making it more permanent. Also, I need to make sure it is easy to change periodically for maintenance. I don't have clamps all over the place because the peristaltic pump produces such gentle flow that it doesn't look like I need it. With the heat here and various weather conditions that may cause problems, I will have to watch it over time to see and learn more. So, right now, the installation looks like this:
I haven't removed all the old tubing and will have to dress stuff up so I don't stumble over it when I go in there, but it works.