My kingdom for a reliable chlorine pump

[Ivan Seeking]

We live in rural area and get our water from a well. Due to the high iron content in the water, beyond all of the normal considerations for purity, chlorine [bleach] is required to react out all of the iron. For years I used diaphram-style pumps that had a life expectancy [based on my experience] of about three years. The last time I bought a peristaltic pump, which definitely eliminates many problems but only lasted three years. Apparently a shaft broke inside the pump assembly.

At ~ $500 a shot, it would be nice to find a pump that actually lasts for more than a few years. Any ideas? They are very low volume - something like 2 gph... maybe more like 1 gph. I would have to check - and adjustable. It must have a discharge pressure higher than the maximum system pressure of about 70 PSI. The pump injects diluted bleach into the system just after the booster pump and before a reaction tank. After the reaction tank it goes through a clarifier that removes the iron (II) chloride.

The chlorine pump comes on whenever the main water pump turns on, so it is intermittent duty, but it can run for long periods of time during heavy water use.

 

[turbo]

Tough call, Ivan. For metering applications with high discharge pressures (defoamer injection into pulp process stream for example) I often specced variable-speed positive displacement piston pumps, but those continuous-duty pumps are VERY expensive and would blow your $500 out the water. Perhaps you can find a lower-cost peristaltic pump. They are very simple critters and someone should be making models with plastic or polycarbonate head housings. Good luck.

Here you go:
http://www.welco.net/

 

[Ivan Seeking]

Tough call, Ivan. For metering applications with high discharge pressures (defoamer injection into pulp process stream for example) I often specced variable-speed positive displacement piston pumps, but those continuous-duty pumps are VERY expensive and would blow your $500 out the water. Perhaps you can find a lower-cost peristaltic pump. They are very simple critters and someone should be making models with plastic or polycarbonate head housings. Good luck.

Here you go:
http://www.welco.net/

If you have any thoughts about industrial pumps that would meet the spec, it may be worth paying much more. But that obviously depends on the life expectancy. I keep thinking that maybe three to five years mtbf may be as much to hope for in any application.

 

[turbo]

If you have any thoughts about industrial pumps that would meet the spec, it may be worth paying much more. But that obviously depends on the life expectancy. I keep thinking that maybe three to five years mtbf may be as much to hope for in any application.

The deal is that with metering pumps, you are paying a premium for precision, much like you pay a premium for a high-precision Fluke multimeter vs a multimeter with all the same features, ranges, etc, without the same guaranteed precision. The pumps that I specced for process-control were generally lab-grade and while they were tough and durable, they were often pricey. I have been out of the chemical process-control field (from a practical standpoint) for about 20 years, so my knowledge of product-lines, pricing and availability are quite dated.

Edit: I'll see if I can rattle a few brain-cells and recall some of the manufacturers and distributors that I used.

 

[Ivan Seeking]

This is defintely not high precision. It becomes a game of trial and error to set the pump to match the average water flow and iron content; both of which are always changing. Over the last twenty years I have learned to read things pretty well but it is still a pain. With the clarifier, carbon filter, and water softner downstream, I have some overhead for sloppy dilution ratios. The large fluctuations in the demand for chlorine are the problem.

In fact I keep playing with the idea of installing a free-ion probe to use as a reference to modulate the chlorine pump time or duty cycle [probably using PID control], but that would get really spendy. It appears that the probes also have a fairly short lifespan and cost quite a bit. There are other ways that I could determine the free iron [post reaction tank] content rather than looking at the free chloride ions, so that is another I'll throw out for consideration. I could probably look at free iron, ph, chloride ions... I can't think of anything else.

Technically, I think it is best to look for free chloride ions as this tells me about all reactive compounds that might be present. Normally you want just a trace of chlorine after the reaction tank, but I'm thinking I can cheat here if it would help.

 

[Gasparri]

We live in rural area and get our water from a well.

Me too. What I did was get some pvc fittings and made a chamber
with a plug hole, and two tubes to pass the water through. These tubes connect
to the pump discharge and the other to the tank. Valves on each tube allow
adjustment of the water flow. Just pop in some swimming pool chlorine
tablets, close the plug and turn the pump on. You can adjust your valves
till you get a .5 to 1 PPM chlorine reading with a test kit.

If you have bad iron problem I'd suggest you get a green sand tank.
You have to recharge it with potassium permanganate once in a
while but the effort is worth it and if you size the tank right
you'll get long runs before needing to recharge.

 

[Ivan Seeking]

Thanks.

Your passive chlorine injection is a pretty clever idea! Doesn't the dilution keep changing, or do the tablets only dissolve to a fixed concentration? How often do you need to add tablets?

I have considered using something else to get the iron, but I know I want chlorine, so it seems a bit redundant to do more. The chlorine works great as long as the dilution is kept in check.

 

[Q_Goest]

Hi Ivan. Interesting that the pumps you've gotten are positive displacement types. Centrifugal pumps will last the longest. I'd suggest looking for a centrifugal pump that's suitable for your needs. I'm not familiar with the particular application you have, so it could be there aren't any centrifugal pumps made for this application. If that's the case, you may also want to consider looking at the designs you have now and see if you can improve on them or add a preventive maintenance (PM) schedule (say once a year) that may extend the life of what you have.

For the shaft failure on the peristalic pump for example, I'd assume stress (fatigue) wasn't the issue. The number of cycles the shaft must have been through after 3 years will certainly be over 10⁸ cycles, at which time fatigue life is infinite. If a part can hit that magic number of cycles, the chance of failure due to fatigue is essentially zero. Maybe a bearing siezed up or the shaft corroded. Can you tell why it failed? Once you determine the cause of failure, you may be able to improve on the part or implement some kind of PM that extends the life of the pump.

For that matter, what failed on the diaphragm machines? Maybe there's something that can be done on those machines.

Typically, things like greasing bearings, replacing diaphrams and valves, or other wearing parts are done on a regular basis in industry to prevent unexpected failures. The best pump for you may be one that is easily maintainable and can be modified to extend the life of the machine.

(PS: I design recip pumps in the 5 to 100 hp range)

 

[Goya]

Have you tried a Venturi tube system? I´ve seen this kind of devices been used by farmers to inject liquid fertilizer into the main watering system pipeline so they symultaniously water and fertilize their crops with the resulting mix.