New metering pump project

[Isaac-1]

As I mentioned in another thread I have decided to install a metering pump to feed 5.25% bleach, the pool is at my elderly mother's house, and I typically only get out there on the weekends, so I am hopeful a constant rate of chlorine injection will make managing the pool easier. I have purchased an LMI metering pump (I know it is not perfect, but was an ebay deal new in the box old stock for under $100) The pump is a P121-151S , .2 GPH max at 150 psi, polypropylene head with ceramic balls, it also has the optional 4FV valve, not perfect, but maybe I can make do, LMI gives polypropylene a fair rating for use with 5.25% bleach, and I can upgrade to a Bleed 4FV or Autoprime valve if need be for gassing issues.

My plan is to install the pump so it feeds from a bulk container (probably a 5 gallon pail until I find something better) and inject into a T fitting installed on the return line just past the filter. I am not sure if I should install before or after the diverter valve for the roof mounted solar panels, any thoughts, it seems to me there are arguments both ways.

This pump has both adjustable stroke length and and speed, is there one or the other that I should try to maximize/minimize to lower the chance of out gassing?

thanks Ike

 

[Bama Rambler]

Sounds like you're on your way. I think PP wil be fine for bleach. I start with max stroke length and adjust the speed first. It'll take a little playing with but it shouldn't be hard to adjust.

Are you going to run it on a timer with the pump?

 

[Isaac-1]

The pump is currently running 24/7 since the last timer died when the pump motor went out a couple of months ago, I plan on replacing it, but that may not happen until the end of the swimming season, when I do I will do something to turn off the metering pump when the pool pump is off. (the plans call for some major remodeling/repair this fall as the metal roof over the pool needs to be replaced, it is 31 years old, so its time)i

Ike

 

[Aquaman95]

Stroke or frequency set too low can cause loss of prime without a degass valve. The good news is you have a low output pump so you shouldn't have to set it too low. The quality of the bleach (which should be pretty good at 5.25 from a grocery store) and the ambient temp will effect it as well. Keeping it well shaded will help.

Polypro should be just fine for 5.25%. The bigger thing to watch is the diaphragm. LMI uses a bonded diaphragm that doesn't hold up to bleach that well. If the diaphragm goes, bleach can leak behind the diaphragm and corrode the metal diaphragm stud to the solenoid at which point the pump is ruined. Just monitor it closely for leaks coming from behind the head and replace the diaphragm as soon as you see one.

 

[Isaac-1]

Ok, I have an installation concern I need your thoughts on. The LMI pump installation guide for Non-flooded feed shows I must have a constant uphill run from the supply tank, into the pump then up to the injection point. My problem is the highest point currently on my return line is about 38 inches from center of the 1.5 inch line to the floor. My feed tank is a 15 gallon commercial laundry bleach poly drum which is about 25.5 inches tall. I have a drum top mounting plate for my pump (screws into the 2 inch drum top hole and has a small hole in the center lined up with the intake port on the pump for the feed line), from the bottom of the mounting bracket to the top of the 4FV valve is another 10.5 inches. This leaves me with only about 2 inches of rise to make a 90 degree bend in the line coming out of the pump and continue a constant rise to the feed point an injector valve screwed into a reducer T to be added inline with the filter output fitting.

A, Is this 2 inches from the top of the 4FV valve enough rise, or will I have problems with out gassing in the line?

B, Should I turn the reducer T to face up, then add a 90 degree fitting (street elbow?) to give me another couple of inches to the injection site, but leaving the potential for a little trapped air in the line?

C, raise the whole filter assembly (big headache replumbing)

D, Change to a different type of feed tank (I don't know what)/ build a shelf and use this one laying on its side in with a semi-flooded pickup and pump mounted lower? If so refilling could be an issue as I would have to build some sort of feed pipe/funnel 90.

thanks for your thoughts
Ike

 

[Bama Rambler]

I think you'll be fine. If you have issues with it you can change it then.

 

[Isaac-1]

Well I installed my LMI pump tonight, so I thought I would share some details on what I ended up with (photos coming tomorrow, hopefully), first the technical stuff:

The pump is a P series LMI metering pump, model P-121-151 as mentioned above, it was sold as new in the box on ebay, it turns out that was some ones on the shelf spare, and some of the accessory items were missing, namely the tubing, the foot valve weight and 4FV valve, everything else was there, it appears unused, factory plugs were still in the holes for the liquid end, foot and injection valve. I ended up using a 15 gallon poly drum commercial laundry bleach container (it even has the correct Corrosive Haz-Mat label and ingredient list), I have the pump mounted on a drum top adapter that screws into the 2.5 inch fitting with a hole for the suction line to draw through. I ended up adding an inverted T fitting to my return line leaving the filter with a 24 inch section of 1.5 inch PVC rising up from the T terminating in a 1/2 inch reduction fitting with a brass T screwed in, one side with a garden hose style gate valve to bleed air and the other with the injection valve from the metering pump. I know this may give me a semi static water column, but I am hopeful the relatively short length to diameter ratio will allow for fairly even water exchange. If nothing else it should even out the mixing of the bleach pulses from the metering pump, currently set at 3 pulses per minute, maximum stroke. (.22 ml per stroke X 3 strokes per minute X 1440 minutes per day x 7 days per week = about 6.6L or about 1.75 gallons gallons per week) I will tune it up from there if it does not maintain a steady ppm, I just don't want to overshoot. There are still a couple of fine tuning items I need to deal with, like get a one way 3/4 inch check valve to allow air in the drum as the bleach is pumped out ( I plan to use a poly T on its side with a ball valve on top and the check valve on the side that way I can put a funnel in the ball valve and open it to refill the drum (hopefully I can find one in PVC with screw fittings). I am not worried about positive pressure since the suction line feeds through a simple rubber stopper that would blow out under fairly low pressure lifting the foot valve with it, then drop back in place. Lowes sells the 3/4 inch check valves for about $7, they are just out of stock at the local store.

Ike

Ike

 

[Bama Rambler]

Excellent write-up. I can't wait for the pics.

 

[Isaac-1]

Here go some photos taken from a cell phone with limited light, sorry about the quality also, pardon the mess and the water on the floor, some fitting started leaking after all the work (I finished a bit after midnight last night, and it was still around 90 degrees in the pump room)

Ike

 

[Bama Rambler]

I really like the fact that you found a bleach drum to use. Where did you get that?

I only see one thing that I would change. The stand of pipe where the injection is connected is large and long. I think it's going to take a lot of bleach to fill it to the point of being injected into the return stream. I mention this because I think it'll affect the ability to control the FC. Once you've gotten the amount of chlorine in the pool you want and shut it off the bleach left in the pipe will continue to diffuse into the water left in the piping and keep slowly adding FC after the pump is off. You might be able to overcome that but injecting the chlorine directly into the return stream would prevent that.

 

[Isaac-1]

The bleach drum came from a commercial laundry program auto dispenser. Specifically from the local hospital, one of my families businesses is a janitorial supply company, the local small hospital is our only customer that uses the 15 gallon size drums, they go through about 2-3 per month of bleach. So I had the salesman that handles their account pick up a couple of empties (the empties seem popular, it took several of his weekly sales calls before they had one on hand), as chance had it he picked up 2 and one turned out to be bleach, the other was laundry break or laundry sour. Many mid size motels use similar dispenser systems, smaller ones use 5 gallon pales or proprietary bulk containers, larger ones use 55 gallon drums, or even multi hundred gallon totes. I too have concerns about the 24 inch long 1.5 inch PVC column, I was going to use 3/4 inch PVC, but was worried it would flex too much or not support the weight of the brass fittings, after running the numbers the volume of that 24 inch section of pipe is only about 1/5 of a gallon it looks like it should be more, but that is the way of tall thin cylinders, and I am sure there will be some slow water exchange due to turbulence in the T fitting. Even if it does somewhat randomly mix 1/5 gallon of 5.25% bleach is only about a .3 ppm FC change in the pool according to the pool calculator, I worry a bigger variation may be due to outgasing in the suction / injection line, so I kept them as short as practical.

 

[Isaac-1]

Just an update for those that may refer to this in the future, at the time I installed the LMI pump I had some tri-chlor pucks in the floater (I needed to bring up CYA a little) therefore it was 5 days from the time I installed the pump, until the FC levels were right to run it, during those 5 days (well closer to 4.5) there had been significant outgassing by the bleach, enough to leave about a 1 inch gas space at the end of the tubing by the injection valve (tubing is polyethylene 1/4 inch OD, probably about 1/8 inch ID), and numerous small bubbles along the line. The pump had no problem with priming and cleared these bubbles from the tubing within a couple of minutes. I therefore suspect I will have no problem with outgassing during normal operation even if I do switch to using a timer and only running the pumps a few hours per day.

Ike

Note I have also added a one was air break valve to the 3/4 inch drum fitting, it will let air in, but not out.

 

[aiannar974]

3 years later, how is the pump working? would you recommend it for acid?

 

[Patrick_B]

3 years later, how is the pump working? would you recommend it for acid?

I would not in that configuration. It might be OK, but I prefer PVDF liquid ends for acid. Even HCL. Others may disagree, but you can't go wrong with it for acid. I know from experience that the LMI PP liquid ends hold up very well to bleach injection, even 12.5% neat bleach. Perhaps not the best first choice, but they hold up.

I just sent an LMI AA171 to P&C in Arlington for repair. After ten years, the diaphragm gave up, leaked behind, corroded the stud, and I couldn't get the diaphragm off. They did, replaced it, and it's pumping bleach right now for a little muni-water sytem we own. It cost me less than 150.00 for the repair and I expect at least a few more years out of it. Some milage varies, but I have had a lot of good luck with LMI for many years.

 

[Isaac-1]

Sorry for the delay getting back on this one, I have been out of town the last couple of weeks, and must have missed this in the preparation for the trip. Overall things are still going good, however I did replace the pump earlier this year with a very similar LMI A941 pump body which has digital speed control that I bought off ebay, as the old one seemed to have developed a problem with its electronic timing where the injection rate would vary considerably with temperature changes. I do find that when using 6-8.25% bleach that the diaphragm must be replaced ever 12-18 months to avoid leakage and that the stainless steel springs in the injection valve, etc. do corrode (I have been changing these springs out with the diaphragms as they can be bought combined in a "service kit", even though it looks like they are no where near the failure point).

Ike

p.s. I stuck with the LMI pump on the replacement because I found a deal on one new in the box, but that was missing the associated accessories, inlet, outlet, foot and injection valves , and was able to reuse the ones from the old pump

Oh, also I had to replace the brass/bronze fitting and hose bib faucet that the injection valve screwed into with Nylon parts, as the chlorine complete ate through the brass/bronze within a year or so.