MHM
New Member
I've got a water intake from a lake for 2 outside spigots that are used primarily for watering the lawn and garden. When installed last year, the plumber put in a 1/2HP pump and only a 2 gallon expansion tank with a 38 PSI charge. The lift from the lake to the pump is less then 10' and the run is around 50'. It was a problem from the beginning with the pump constantly cycling off and on. My complaints about that fell on deaf ears. Now, after less then a year the pump relay contacts burned out and I have his attention. He will now replace the pump and put in a larger expansion tank. The question is how large a tank? The local plumbing supply house recommended a 39 gal tank through my contractor but I don't know what they based it on. The plumber says a 10 to 20 gal tank would be fine. He says anything bigger would result in a slow draw down which I would see as a slow reduction of the pressure and a marked difference in the sprinkler coverage from the pump cutoff to when it kicks back on. From what I can find a typical sprinkler will use around 10 to 15 gals per minute, so running 2 sprinklers will draw down a 20 gal tank (~7 gal drawdown?) in well under a minute. That doesn't seem adequate and even a 39 gallon tank seems marginal at best. What size tank should I use and will I really notice a big difference in the sprinkler coverage between a small and large tank? (I would think that the coverage should be the same at the turn on and turn off points of the pump independent of the tank size but he's saying that with the small tank it's barely noticeable since it happens so quick. That's the part I don't buy.)
Thanks,
Thanks,