Pump Recommendation

Zman

I am working on a project in a 6,000 square foot custom home.
The home has a deep well that can't keep up with demand. As a solution, someone installed a couple 200 gallon (5' tall) non pressurized storage tanks, a booster pump and well pressure tank. The well keeps the storage tanks full and the booster pump pressurizes the house.

The problem is that the booster pump frequently air locks due the the fact that it only has 2'-5' of head pressure on the inlet. The fact that the home is 10,000 feet above sea level (~10 psi atmosphere) isn't helping much either.

The home requires about 15 gpm @ 70 PSI

Here is the installed pump and system curve. The sizing is about right, the NPSHR is a problem at 5.5'
Does anyone have a suggestion for a pump with lower NPSHR requirements? Shallow well pump?
Thank you in advance.

Jamie Hall

With that combination of flow and suction head, I'm sort of surprised that it works at all.

If you could find a shallow well jet pump with that combination of output flow and pressure, it would probably work. However, that's a pretty big if.

The cheapest solution -- if the facility is arranged to permit it -- is to relocate the pump 10 feet lower (or the tanks 10 feet higher...). Be very careful about the inlet piping -- large diameter, long sweep bends if any are necessary, full port valves, a couple of feet of straight pipe before the inlet to the pump -- the usual.

Not so usual, provide an anti-vortex set of baffles at the inlet from the tank. These will be needed for any external pump.

Somewhat more expensive would be an irrigation type pump with the ability to operate with a suction head.

Steve Thompson (Taco)

Assuming the booster pump (not the pump supplying the water to thee storage tank) is installed close to the water storage tank and has minimal, unobstructed piping between the water tank and the pump inlet you should have sufficient inlet pressure. NPSH is absolute pressure. So at 10,000 ft, assuming atmospheric pressure is 10 PSI (it's 14.7 at sea level) you have 10 PSI x 2.31 or 23' NPSHa (reality is 23' less elevation and suction piping losses).

I would check for leaks in the suction line (suction lines can draw air). Where is the pump installed on reference to the storage tank?

Pumpguy

You might look into a 2 foot NPSH pump. These pumps are really 2 stage type, using an axial flow prop ahead of the centrifugal impeller.
These pumps are usually used for pumping high temperature condensate from a steam heating system, but this may work for your application too.
SHIPCO is one manufacturer, and I believe the old ITT Hoffman / Domestic made them too.

Solid_Fuel_Man

Can you replace the two non pressurized tanks with to diaphragm well tanks? Would definitely be an expensive solution as I think the hundred gallon ones are only about 25 gallon drawdown.

Zman

Steve Thompson (Taco) said:

Assuming the booster pump (not the pump supplying the water to thee storage tank) is installed close to the water storage tank and has minimal, unobstructed piping between the water tank and the pump inlet you should have sufficient inlet pressure. NPSH is absolute pressure. So at 10,000 ft, assuming atmospheric pressure is 10 PSI (it's 14.7 at sea level) you have 10 PSI x 2.31 or 23' NPSHa (reality is 23' less elevation and suction piping losses).

I would check for leaks in the suction line (suction lines can draw air). Where is the pump installed on reference to the storage tank?

@Steve Thompson

I am going to take a look again today. I am suspect of a union and balancing valve on the suction side allowing air intrusion and creating drag.
The solution may be to upsize the 1" copper on the inlet side and perhaps put a balancing valve on the outlet to keep the flow rates in check. I realize that 15 GPM is pretty fast for 1" copper pipe on the discharge side, it is just a short run with intermittent use.

STEVEusaPA

Water tower?...jk

hot_rod

seems you would want a booster pump like this.

https://us.grundfos.com/content/dam/GPU/Literature/CM-CMBE/LCMBSL01-0615-CMBE-Brochure.pdf

Jamie Hall

Actually I'm not sure that it really is a NPSH problem -- although it may be. It may also be a vortex problem at the inlet from the tank. Whatever you do about the pump, installing anti-vortex baffles at the inlet is going to help.

And it's true that the apparent NPSH at the pump looks as though it should be enough -- and assuming that the head loss at the entrance is small, and that the piping is adequately sized -- which if it is 1 inch and any length at all it isn't -- and that the balancing valve has no flow restriction -- which seems unlikely -- it might be.

On the whole a very marginal installation.

Zman

hot_rod said:

seems you would want a booster pump like this.

https://us.grundfos.com/content/dam/GPU/Literature/CM-CMBE/LCMBSL01-0615-CMBE-Brochure.pdf

@hot_rod
I was looking at that one and became concerned about the altitude and cooling. I seems like going oversized by one model and then turning down the pump would help.



In either event, I plan to go with 1 1/2" pipe on the suction side and raising the tanks a few inches above the pump.

The rest of this house could win a heating hell award. 500,000 BTU's of boiler in a 3.5' crawl space. I will post it if the pictures turned out well....

SuperJ

EDIT: HR posted a all in one solution. My experience was about 10 years ago. I agree with the oversizing one notch.

I've had good luck with the variable speed grundfos pumps (mostly the SQE deep wheel pumps though), typically you put a small expansion tank (2gal) on the outlet and then a check valve. They will vary speed to maintain a constant outlet pressure, and have intelligent protections against running dry. Might be less likely to air lock since it won't be running full speed often.