Booster pump erratic operation-Help!

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Raucina

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I thought I knew a bit about pumps, but I am stumped. Well water is fed to a 3000 gallon tank, then feeds to a distribution building via 2" pvc pipe. No filters or restrictions in feed line outside of a valve and checkvalve. A Myers
[8stage?] horizontal booster pump, 1hp then feeds a standard pressure tank. I also have 2 backup pumps at 3/4 hp with about 6 stages that can be put in service if needed. Typical pump switch pressure setting is 60-80 psi.
There is 6psi at the pump inlet from the elevation rise of the storage tank.

The problem is that the pressure boost on the 8 stage unit rises to 50 psi, then very reliably hesitates and drops to 48 psi where it stays "forever", probably until the water would boil in the pump. Ok, so I popped in the smaller pump and it stops boosting at 62 psi and drops to 60 where it stays.

Is this cavitation? Why at different psi's on each pump? I have searched for suction leaks and cannot find any. This same set up worked reliably for years- cant think of any new elements in the system. Pumps are not very old and the water is very clean. Any ideas appreciated!
 

Bob NH

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You may have something that is restricting the flow so the pump overheats the water, causing cavitation.

Try opening a line to discharge a little water and see if that helps the problem.

There could be a restriction in the suction line.

Is it possible that you have a leak in a discharge line that is losing water when you get to high pressure? Maybe a valve cracked open? Or a leak in an underground line?
 

Jadnashua

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Is the valve a full-port valve? Is the check valve actually working, or maybe partially stuck?
 

Bob NH

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Air in the Suction Pipe?

Another possibility is that you could have air in the suction line if it has any high spots between the tank and the pump.

The effect is that a bubble can restrict the flow through the pipe, and that will limit the ability of the pump to develop pressure.

One possible high spot is in the tank. If it has one of those elbows inside the inlet, get a stick or other means and pull its inlet is horizontal, so that any bubble can escape.

If there is a high spot in the pipe, you will have to find a way to make sure there is no air trapped at the high spot.
 

Valveman

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Valveman

I would still bet on a suction leak. They are very hard to find, but they act just like you are describing. Pump works fine at low pressure and high volume, but as pressure increases flow decreases. When the flow rate is reduced at 50 or 62 PSI, it is easier to suck in air than water, pressure drops slightly and pump looses prime and gets hot. While pump is running and pumping water, dab PVC glue in threaded and glued fittings, you will see the glue suck into the air leak. Glue might fix the problem or just show you where it is.
 

Raucina

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Thanks for your time to throw me some ideas... I had previously installed a three way valve into the system that allows me to bypass the storage tank [static, 3,000 g] and directly pressurize the system from the deep well. So using your idea to search in a new way for suction leaks, I opened an isolation valve and back pressurized the booster pump. This of course told me the check valve is okay, and allowed me to search for leaks with soap [there was air remaining in the pipes] So I found the smallest leak at a union - that never leaked WATER. Okay, fixed that, and still no reliable pressure output from the pump. When the pump reached about 65psi. you could hear a slight "churning" sound - sort of a woosh, and then the pressure dropped 3 psi and remained. Air bubble lurking in pipe? Outlet is clear hose, so easy to check that- angled pump up to allow air out - nothing. Then I decided to allow the back pressure to remain inthe pump for a day, maybe to allow the water to absorb the air... restarted the pump while still under back pressure, [then changed the three way valve] and now it seems to work. Interestingly, there is still a hesitation at about 65 psi, but the pump seems to push past it. Still the pump will not pressurize from zero pressure in the pipes. Very strange. What do you guys know about air-entrained water? Water in a clear glass from the system throws a lot of tiny bubbles when allowed to sit awhile... Can my well water itself be the source of the problem? Why are these horizontal booster pumps so sensitive to air? Most pumps push air right through... can it be the small diameter of the impellers? Thanks again...
 

Valveman

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"Still the pump will not pressurize from zero pressure in the pipes." This does not make sence to me. How do you ever get it started pumping? If your water in the 3000 gal tank does not have air entrained, the problem is not your water quality. Air is getting in through a suction leak or from being churned up from the impellers spinning and not moving water. You said you added the three way valve recently, the packing through the stem could be your suction leak. You messed with the three way valve and now it works better? Sounds like a connection there some where!!! These multistage type pumps are no different than any other pump when it comes to air or suction leaks. Let us know when you figure out the problem. Keeps us from just scratching our heads and helps us with the next one down the road.
 

Raucina

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booster pump mystery continued

Valveman, you were right about the suction leak - actually I had previously tried soap on the suction end of the pump plumbing to see if i could see it being sucked in... would have tried glue except that some of the pipe is stainless steel and many connections are threaded sch. 80 pvc, so didnt want to make a mess. The three way valve is downstream from the pump and not on the suction end, not a player in the problem. The valve redirects the static storage tank infeed from the deep well directly to the distribution system. What I called an isolation valve, simply blocks off this water to the booster pump and pressure tank so that you can service it. I know it sounds stupid, but sometimes the pump WILL pump from zero to 80 psi, and at others it will just pause at 20 or 50 psi and churn water and what sounds like air. Today the system is working and I dont want to risk reducing the pressure to zero and try and test it. I found the Myers manual and it mentions throttling the output if there is cavitation - is that something I should try?
 

Valveman

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If you do not have a suction leak and the pump starts its churning at low pressure which means high volume, then you may be cavitating from trying to pump water faster than the pump can get water. Throttling the output will keep it from pumping water faster than it can get it. Sure won't hurt anything. Throttling is also a good way to check for suction leaks. When you throttle the output of the pump to very low flow, you will quickly loose prime if you still have a suction leak. At high flow there is enough water moving that the air leak dosn't take over. At low flow it is easier for the pump to suck in air than water, and a suction leak will cause you to loose prime.
 

Raucina

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New pump ideas?

that sounds about right to me, I will try to restrict the output. Of course since this system is designed to run a few 1" rooftop rainbirds for wild fire protection [california mountains] it will add a potential problem in an emergency. Every above ground pump I have used is problematic, except for some 3phase units at my business. Submersibles seem to last forever comparably - maybe I should toss one into the storage tank and forget the boosters? The GE motors on these myers pumps are just junk, touch the starting assembly housing and it cracks to pieces, even a new one came with a crack, and within a week threw off the spring on the start switch - and again a month later. And myers fiddled with the frame size and thread so no other motor will work - strictly a myers item... Is there a reasonably priced pump that will pass some air and push up to 70 or 80 psi, maybe 18gpm? Hopefully with electronic starting....
 

Bob NH

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It's hard to beat a good submersible for performance and efficiency. They would give you the most options to meet your needs.

Outside the tank, I would use a multistage centrifugal like the Goulds 2 HP HSC20 (20 GPM at 80 PSI).

If you are pumping to a bladder tank, you will need a big tank (or tanks) to provide at two minutes of drawdown for adequate "motor off" time.

I don't know what you mean by "electronic starting" but it is a capacitor start single phase motor, industrial quality.

Your requirement of high pressure and modest flow dictates a multistage centrifugal. With the flooded suction (6 psi inlet pressure) a LITTLE air should not be a problem. If you have an adequate line from the tank, your pressure at the pump should be above atmospheric pressure and you should not have an air problem. How far are you from the tank?

If you have a hump in the inlet pipe that is trapping an air bubble, you need to fix that for any pump system.
 

Valveman

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At least with a submersible you would not have to worry about a suction leak or too small a pipe starving the pump. The problem with the equipment you are seeing is called "planned obsolescence". Almost everything manufactured today is de engineered for "planned obsolescence". See the following : http://www.cyclestopvalves.com/homeowners_4.html
 

Raucina

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The pump feed is 2'' within 2 feet of the inlet, one elbow in the line, no traps or humps in pipe. Judging by the sparkling water industry, some wells have gas built into the water - churn it up and it comes out? I do see drinking glasses lined with air bubbles after a short rest.

Electronic starting is the same as on 3 wire submersibles - no centrifical switch telling the start windings to shut down - the micro chip figures it out in a better way. Probably why they last so long. And 3 phase beats all with no starting circuit needs at all. Yes, planned self destruction in order to be the low cost leaders. This cycle valve sounds good, thanks.
 
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