Well pump slow down (a bit long)

[Treetops]

Lately my well pump has been taking a long time to get to shut off pressure. When I am using 8 -10 gpm continuously (running my geothermal heat pump), the normal duty cycle of the pump was about 66% i.e. it ran for

4 minutes to get to shut off(60psi), then for 2 minutes to get to turn on pressure (40psi). This has been the case for the last 10 years.

Now the off time is still 2 minutes but the pump runs (at 8-10gpm) for upwards of 45 - 60 minutes before it reaches shut off pressure. Also, in the past, I could run 18gpm steady and pump would hold 55 - 60 psi. Now the best it will do is 12gpm steady but pressure will not get above

27psi. Pump is a 1HP submersible Gould 10GS10412 3 wire with an 85gallon diaphragm pressure tank. Pump amp drain is normal at 10amps. Well is 200ft deep and a static water level at 45 ft. and was rated at 40gpm when drilled 10years ago. Pump is at 160ft. Terrain is granite and I have never had any problem with water supply; lake is 100ft away and 50 ft below well head. Pressure in system holds at 60psi when not used or pumping. Water is moderately hard with moderate level of iron bacteria. No sediment.

People, could you give me your ideas on what might be going wrong here?

Pump motor was replaced after first 5 years due to motor winding failure. Now its another 5 years and trouble again. Same model of pump. Is it the type or brand of pump? (assuming I have a malfunctioning pump)

At this time of year, it is not unusual for the heat pump to be running

24/7 for days on end. In a normal winter, the heat pump may be on 50% of the time for 3 -4 months. So a lot of pumping but I understood this pump should be up to it. But maybe I'm misinformed???? Is this kind of problem a normal failure mode after heavy use? What would be an expected life under these conditions?

Thanks for your input!

[dpb]

...

Sounds like worn impellers. When changed/rebuilt motor, most likely didn't do anything to the pump. W/ time you've now just basically worn it out. It's possible there's a leak in the system somewhere, but 10 years of which roughly half is nearly continuous operation is a lot of operational time. You can probably limp along for a while, but the increased run time will shorten motor life, so would be best to try to get it solved as soon as conveniently possible. It will only get worse and since you already are seeing sizable pressure drop, it's going to continue to progress. You're losing operational efficiency on the geothermal system as well as pushing the point at which you may have a catastrophic failure ultimatly if don't get it taken care of.

BTW, had geothermal, albeit closed loop ground source system in TN and loved it...are you recycling water or is it once-through?

[Treetops]

Dpb Thanks for the reply.

Impellers are quite probably the answer but I was thinking that since I see no sand or grit in my water, I didn't expect significant wear. Also per the manufacturer's blurb "face clearance floating impeller stack proven over 40 years as superior sand handling durable pump design". Also this problem seems to have developed relatively quickly as I have noticed the reduction only over the last 4 - 5 months. So I thought something else may be the culprit. But then I'm no expert on pump wear and lifespans.

WRT a possible leak. Would I not see a drop in pressure when the pump is idle?

As pulling a pump in winter here (Quebec Canada) is not too pleasant, I think I will monitor the pump output and may try and limp by until spring. Will have a contingency plan for heat though!!

My system is open loop with the water disposed into a stone pit which then drains into the lake. Love the system and the yearly cost is about

1/3 of the cheapest alternative. Also SAFE!!! No combustion, high temperatures, gases or pollutants.!My last house suffered a massive oil tank leak contaminating the basement and ground. Worst part, this was in Massacheusets, a state with the most severe environmental rules regardong ground contamination. Cleanup was a real nightmare! No more oil for me!

[dpb]

That it's fine so that it's not visible doesn't mean there are dissolved and other sediments. Wear is inevitable and you're talking a lot of running in the mode you're using it as compared to a typical well-supply. And, "proven over 40 years" doesn't mean a 40-yr lifetime, but implies the manufacturer has 40-yrs of development/experience w/ the design. As compared to some other design/material, it's quite possible it is superior.

The relatively rapid change is also characteristic of pumps and similar mechanisms in general. The pressure loss is highly dependent on clearances and drops quite rapidly as tolerances are lost. Same thing is true w/ air handlers, vacuums, etc. That's why you may lose essentially all performance.

Probably, depending on where any leak is compared to the pressure measurement point, of course. But, in general, I think it unlikely, agreed and that the problem is the pump itself and either impeller or housing wear (or a little of both) is, imo, the most probable cause of the symptoms as described.

I gather this isn't also potable water so that losing this pump doesn't affect that...

[Treetops]

Thanks again for your reply!

Your comments on dissolved minerals and wear, as well as on clearances and loss of performance make sense to me and appear to explain my problem. So I'm probably looking at pulling the pump in the near future. Maybe we will have another balmey day this January!! (Two days ago temp was 45F:temp tonite is forecast to be -5F and -25F tomorrow nite)

One other possibility, which I think is remote, is that the static level of the well has lowered from 45ft to 120ft or lower. According to the pump curve, this would explain my lowered output. I haven't measured this level in several years but given the stable nature of the terrain around here, the record rain falls last fall and the fact the lake level is at 50 ft below the well head and only 150 ft away, I don't beleive this is the case.............and I hate putting something in the well to measure the level especially with cold fingers.

BTW this is my source of potable water but I have a number of 5gal buckets filled to the brim!!!!!

If my pump is the problem, I will have to do some research to find a pump better suited for this application.

[dpb]

What the water table is and the well regeneration capacity and how fast the surface recharge rate is are impossible to tell remotely, of course, but not likely if it's a potable water source that it's at all directly related to the lake level. But, if you've used this well for

10 years prior to this for the same purpose, it's unlikely it's the problem, but not impossible. Unless the groundwater there is pretty quickly renewable and not a problem, however, the once-through nature is pretty high on consuming water. Is it feasible to have a closed loop w/ the lake as the heat source/sink? Then you could use the well only as potable water source and have only a circ pump for the heat pump.

As a deep well pump, doesn't seem like a bad choice and I wouldn't consider a 10-yr lifetime under the kind of usage you described as a particularly short lifetime -- in fact, it seems pretty good to me in comparison w/ our well here of roughly same size and depth.

[jaytaylor5555]

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