Air in impeller? From where?

Maybe you guys have ideas for me: My 3/4HP shallow well pump, for 10-15 seconds on startup, makes a somewhat harsh sound from the impeller that then "smooths out" to be very quiet, as its pumping-up from 40 to 60 psi. This pump's 1 1/4" input is tied not to a well, but to the bottom bulkhead fitting of a storage tank which always has 500+ gallons of water in it (about 8 feet of pipe interconnecting the two, at the same low ground level).

Wondering about the noise on startup--my assumption has always been (this pump has worked fine for a couple yrs now) that somehow there are air bubbles in the pump that the impeller "spins out" then things quiet down. But where would/could air bubbles possibly come from--I'm certain there are no leaks in the intake pipe, and there is always a ton or more of water on top of the intake pipe (it never ever "sucks air" from the tank).

The pump has an integral check valve and serves a large pressure tank w/bladder (below it underground), a couple of Big Blue filters (above it), and eventually a water softener and a couple of pipes to our house & garage.

As I type this the only thing I can think of is possibly air bubbles in the pressure tank below that the pump "trades back & forth" time & again? Gosh, even that theory seems unlikely--any air bubbles should rise UP thru the pipes into the filters and out the system eventually...

Like I said the pump has worked fine, the noise is not actually a problem--just wondering what could be causing this, and assuming if it's cavitation that the impeller life will be shortened thru this?

I don't see how it can be air, unless the pump was cavitating which with flodded suction, it shouldn't IMO. So, think bearings as in going bad.

Gary Slusser said:

I don't see how it can be air

Click to expand...

Well, that's what I thought, but honestly I don't think "bearings" either because it's been doing this from Minute 1 (I bought and installed the pump brand-new), and it runs quiet & smooth-as-silk except for those initial seconds.

One would think if there was an air leak somewhere, I might notice too an accompanying water leak, if only a drip. And if there was an air leak, why would the gurgling last for only a few secs, and not be continuous...

Do you have any air in the water at the faucets?

If not, then IMO it's cavitaing or bearings. Call the folks you bought it from and see what they suggest.

You could have a leaking foot valve allowing a little air in when when the pump is off, but you should see some air at the fixtures.

Yes, there is sometimes unexpected "burping" at faucets... never thought the two might be related (duh).

I bought the pump from Sears; you inspired me to look again at the installation drawings for it. Immediately adjacent to the pump's 1" output is a "Captive Air Tank" connection. I do not have my pressure tank connected here, it is instead a coupla feet downstream from the pump, so I simply put a plug in there.

I wonder if that plug needs re-taping, or is there maybe some magic to the positioning of the pressure tank that I don't understand? I could pipe my pressure tank to this specific point on the pump, but it never occurred to me that it might matter for proper pump operation. The Sears manual does say "Sears Jet Pumps should be used with Captive Air(r) Tanks". But who forheavensake pays attention to stuff like that?

There is also a Priming plug up there (across the impeller housing from the output/airtank connections) which I should check while I'm at it.

Thanks Gary for showing an interest in this! I'm out in the "extreme country" and am (unfortunately for me) the most knowledgeable guy around!

Gary Slusser said:

You could have a leaking foot valve allowing a little air in when when the pump is off...

Click to expand...

I should add, I don't HAVE a foot valve, just an open-ended 1 1/4" pipe sitting in the bottom of this storage tank, which always has 100s of gallons of water on top of it. So I believed I didn't need one?

I have an identical set up, and have had the same sound and "churning" at pump startup. It would seem with a flooded or slightly pressurized inlet that all should work simply, but it is not so.

Your problem if it is one, is on the suction side, so dont look at the outlet at all.

I would add a good check valve just at the pump inlet no matter that sears gave you a nylon one inside the pump, then check religiously for suction leaks
that may draw air no matter that there is no noticable leak outward.

My water, when allowed to settle overnight in a glass shows many bubbles. Perhaps there is dissolved gas in our water that is "exploded" out by impact on impeller start up only. It does not seem to cause any problems [in my case] over time.

Raucina said:

I have an identical set up, and have had the same sound and "churning"... I would add a good check valve just at the pump inlet... Perhaps there is dissolved gas in our water that is "exploded" out by impact on impeller start up only.

Click to expand...

Many thanks Raucina for your comments--very reassuring to me!

I installed the tank in the 1st place as an Aeration tank to see if it alone would clear-up our "smelly water" problem (it did). Our well's since gone dry but I still run water (from our pool & rainwater tanks) into this tallish tank (what a blessing that I had it already in place when the well stopped producing! ) from the top, so there is much splashing that occurs, then the tank is regularly "in-use" so the water never gets too stagnant/still.

Your check valve idea will be easy to try so I'm gonna do it! Probably won't get to it until after I finish my rainwater system (I have a dozen tanks I have to plumb), but when I do I will report back here whether or not the extra checkvalve does the trick.

If not, like you I'll not lose any sleep over this--if there IS impeller wear that is occurring it will be much easier to fix a $300 shallow well pump vs. the $3K deep-well pump it in effect is replacing.

I would think you have an air leak somewhere in the suction line. And the check valve that comes with those Sears pumps should be removed and the valve put at the far end of the suction line in the tank. No other valves are needed anywhere. This way, the entire system is full of water under pressure, so no air can get into the suction line. Just because Sta-rite chose to put a plastic check valve in the pumps they sell to Sears, doesn't mean it's the correct way.

bob...