Jet pump introducing air?

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Old 08-29-16, 07:18 AM
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Jet pump introducing air?

Hi, looking for input on a recent puzzling problem:

I have a household water system which consists of 3 ea. 3,000 gal. above-ground tanks, from which I pull water with a jet pump, into a conventional pressure-tank system (bladder type, 2 year-old tank). The line runs through a filtration system (sediment, charcoal, and UV), and then to the various fixtures in the house.

This system, self-installed 6-7 years ago, has been operating with no issues, but in the past few days, air is somehow being introduced into the system. I've checked the intake in the tanks (1" hoses, floated ~12" below the water surface) and they all appear normal, and I have no leaks evident (visible) anywhere.

To me, the only 2 ways air can be introduced is (1) by the pump sucking air thru the intake or (2) the system being opened and then re-pressurized. I changed filters about a month ago, which normally introduces a small amount of air that works its way through the system in less than a day. While it is possible that an air bubble was trapped somewhere and is just now getting released, that seems unlikely, given that this has been going on for 4 days, randomly, and at various fixtures.

Leads me to wonder whether the jet pump (replaced about 3 years ago) is going south, and the introduction of air is a warning sign. Is this possible? (I'm much more familiar with the characteristics of impeller pumps than jet pumps.)

Thanks for any advice!
 
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Old 08-29-16, 09:28 AM
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It's possible you have a crack or pinhole somewhere on the suction side of the pump. Air doesn't necessarily have to be sucked in at the intake. It can suck in air anywhere along the suction path; piping, fittings and even pump housing or shaft seal.
 
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Old 08-29-16, 02:39 PM
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Yes, that's true, and that was the 2nd thing I looked for, however on the suction side there is a constant head of anywhere from 3 ft. to 9 ft., depending on how full the tank(s) is/are, so I'd think I would see a leak. Hard to say how much air is getting in, but it seems to be enough that a break of any kind would at least drip.

Thanks!
 
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Old 08-30-16, 12:18 AM
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Hard to say how much air is getting in, but it seems to be enough that a break of any kind would at least drip.
Not necessarily.

How much air IS in the system ? How do you know it's there ?
 
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Old 08-30-16, 04:27 AM
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3-9' of head isn't a great deal of pressure. When your pump is operating it may drawing the equivalent of 30' and the leak might not be visible at the lower pressure. It only takes a tiny crack or pinhole to allow in a surprising amount of air. The pump impeller can break the air up into tiny bubbles making it appear like there is more and once in the system air can accumulate in pockets which can also give the impression that there is a lot getting into the system.
 
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Old 08-30-16, 09:40 AM
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How much air IS in the system ? How do you know it's there ?

How do I know it's there? When air spits and sputters out of the faucet, in the toilet tanks when flushed, in the washing machine when it's filling, it's pretty clear that air is in the system. Don't know what else it could be.

Per my OP, I frequently have a little air in the system after a filter change, for a short time, so I'm pretty well aware of what's happening.

Obviously I don't know what volume is involved, but it isn't a great deal, from a few to a number of seconds at the fixture, depending on how high the water flow is. Not consistent - may go a day w/o noticing it, but it seems to be more prevalent first thing in the am for some reason.

Thanks.
 
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Old 08-30-16, 09:58 AM
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3-9' of head isn't a great deal of pressure. When your pump is operating it may drawing the equivalent of 30' and the leak might not be visible at the lower pressure. It only takes a tiny crack or pinhole to allow in a surprising amount of air. The pump impeller can break the air up into tiny bubbles making it appear like there is more and once in the system air can accumulate in pockets which can also give the impression that there is a lot getting into the system.

OK, granted, there could be a tiny leak at a PVC ball valve on the intake side, for example. Not sure how to find that, are you? (Testing with compressed air would be quite difficult.) I needed to open and close 2 valves ~2 weeks ago after they'd been in one position for probably a year, so that's the only thing that's been disturbed - but no air showed up in the system until a few days ago.

Just noodling here, the pump will draw water (or air) from the path of least resistance, so it seems to me that the 1-1/4" intake line (attached to the 1" hoses inside of the storage tanks), WITH positive head, has much less resistance than a minute crack or pinhole. I could see it drawing in air from a pinhole, etc. if it were pulling water from below-grade, for example.

I appreciate the advice, but I'm still wondering whether a tired jet pump could possibly induce air w/o such a leak as we're discussing here.

Thanks.
 
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Old 08-30-16, 10:54 AM
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Many times the answer to a problem is right under our nose but since we aren't there we can't see it. Can you post a few pictures of your setup there ? http://www.doityourself.com/forum/el...-pictures.html
 
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Old 08-30-16, 12:24 PM
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Yes, I can do that, will post a bit later....
 
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Old 08-30-16, 04:12 PM
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If there is a spot you suspect you can smear Vaseline over the spot and see if that stops the air.
 
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Old 08-30-16, 04:13 PM
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System pics. . . and a suspect!

Pilot Dane, you got me to thinking harder about the possible sources of air being sucked in, in spite of the absence of an obvious leak. (Love these forums!)

While the jet pump was running today, I put my hands all over various fittings to see if I could somehow find the air source. [The pump I currently have installed has a SS body, and the piping to it is schd. 40 PVC. The threaded (female) inlet on the pump has been something of a problem child since I put the pump in service. I re-sealed the threaded connection a couple of times with different teflon tapes (pink, blue) but it continued to have a slight drip. Finally, it resolved itself after a few months, but I'd never had any trouble with air in the system before now.] Today when I wrapped my fingers around that connex, it was slightly damp on the bottom, and I will swear I felt a slight suction (really? or my imagination??). Loosened the union and I was able to snug up the pump connex about 3/4-turn w/o over-tightening (hmmm, maybe.. .).

So, I will see, over the next couple of days, whether this was the perp. Should know by Friday, so will re-post with results by then.

In the meantime, as requested by PJMax, I'm including photos of the system. These were taken about 4 years ago, and since then I've put the new pump and a new pressure tank, but the config is exactly the same. (Including the temporary wiring to the jet pump ) Maybe you guys will see something that doesn't look right? (As you will notice, this is a rainwater collection system - we use it for all household water needs. Well is a backup.) Thanks again!

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Old 08-30-16, 06:37 PM
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Thanks for the pictures.... pretty cool setup.

I labeled one of your pics. As long as the A valve is closed... everything in blue is under pressure and won't cause any air introduction problems.

Everything in red is under a vacuum. I have to tell you.... I have those unions (C) on my pool pump and they are a bear to seal for vacuum. I ended up using silicone on the mating face to seal it. I know the silicone will break loose when I open the connection.

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Old 08-31-16, 07:08 AM
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Thanks for the comments and for taking the time for the mark-up. I had not considered the unions to be suspect, but your solution is a good idea if the snugging-up I did yesterday doesn't solve the problem.

I have had several instances of leakage in the past with female SS or galvanized threaded connections to PVC male adapters or nipples. It seems to be due to our high summertime temps here in TX, expanding the metal more than the PVC, that causes the trouble.

In this instance (the new/current pump having a SS body & coupling on the intake), I really need to swap that PVC male adapter out for a SS nipple, and thread that into a PVC female adapter, in order to permanently fix it. My pumphouse is insulated but not cooled, so it gets pretty hot in there on 100-degree days.
 
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Old 09-02-16, 09:21 AM
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Nuts! Still some air

Still getting some air in the lines, although it seems to be about half (?) of what it was, so maybe I'm on the right track. Took apart the threaded joint at the pump and re-sealed it, and noticed the pump outlet was seeping too; tightened it, but still leaking. . . as is inlet side . Next trip to "the big city" I'll find a SS nipple for the inlet side and re-pipe it to see if metal-to-metal seals better, using pipe dope. (Also will employ the silicone trick on the union, suggested by PJMax.) Outlet side will require some thinking, don't have much room to play with unless I do a major revision of the piping.

What the heck is up with this SS pump body?? Wonder if the fact it is Italian-made has anything to do with it; maybe the couplings welded to the pump body were not threaded perfectly?

More later. . .
 
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Old 09-07-16, 06:29 PM
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The final solution: It wasn't "air" in the plumbing!

Posting this info in case anyone else has a similar issue. Turns out, what seemed to be air in the piping was in fact GAS being generated in the electric HW heater. I believe this was hydrogen gas, which is flammable (oops).

Noticing that most of the "burping" was happening from the HW lines, and after heavy use of hot water, I started looking into why that might be. Found a forum on which it was mentioned that a busted heating element can cause gassing in the water heater. Drained the heater and removed the elements, and noticed the inside of the heater was badly corroded (16 years old).

New heater in place, and no more gas/air in the lines!! Apparently, the gassing in the heater was also back-feeding into the house's CW lines as well.

Ya learn something new every day, huh?
 
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Old 09-07-16, 06:53 PM
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Ya learn something new every day, huh?
You can say that again. At least the problem is solved.
 
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Old 09-11-17, 07:37 AM
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Thanks for sharing such useful information.
 
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