Pressure tank configuration as source of flow problems

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jgdyer

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I am troubleshooting poor water well performance in my house, built in 2001. The house is 2 story, elevated on pillars above a flood plain, so essentially 3 story.

Flow performance has always been mediocre.
I just replaced a .5 HP 10 GPM submersible pump with a .75 HP 10 GPM pump with no apparent change in performance.
Well is 45 feet deep.
The well installer calculated pump curves, and we agree I should be getting better flow, but other than proposing I might have a restriction of some sort in the plumbing, he has no suggestions.

Delivery:
18.9 GPM at ground floor from a frost proof hydrant
8.3 GPM at level 1 from a laundry sink, both valves open, no flow restrictor in spout
2.5 GPM at level 2 in the shower with the wand removed, no flow restrictor

So, having eliminated the whole house filter and the water softener as culprits, my attention now falls upon the pressure tank.

As you can see from the layout in the furnace room at level 1, the plumber did not plan his installation very well. Lots of ells and tees and branches ...

The pressure tank installation is not conventional ..

A 3/4" leg off the 1" supply runs down to the tank
A standpipe comes off the tank leg to serve the gauge and pressure switch, both positioned higher than the top of the tank

After doing a little reading, I surmise that this setup can result in, at least, slow tank drawdown and an inaccurate pressure reading at the gauge. And, therefore, pressure switch settings that do not reflect actual tank metrics.

I wonder, too, if my tank isn't forming a hydraulic "speedbump" of sorts that is affecting flow across the supply line when the pump is running.

I also wonder if there is any way of fixing this short of going to a variable speed pump.

Suggestions, anyone?
 

Valveman

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The pressure switch is what determines the pressure the pump operates at. It doesn't help to put in a bigger pump if your pressure switch is still set at 30/50, then 30 to 50 is all the pressure the house will see. The 1/2 HP could have easily run at 40/60, and the 3/4 HP can easily be turned up to 50/70. You didn't say what pressure your switch was set at, but I am guessing 30/50. Just tighten the big adjustment screw in the pressure switch until the pump starts at about 50 and goes off at about 70.

Of course your tank is too small to be running at 30/50 with that size pump. So it is really too small for 50/70, which will make your pump cycle on and off a lot. Even the pressure swinging from 50 to 70 while taking a shower can make it seem like the pressure is low. That tank is plenty big enough when used with a Cycle Stop Valve. A CSV set at 60, will hold 60 constant while you are in the shower, which gives much stronger pressure than when the switch keeps cycling the pump on and off between 50 and 70.

Stay away from the variable speed pumps unless you like jumping from the frying pan into the fire. Those varible speed pumps are making the pump manufacturers rich because there are so many gullible people falling for the hype.
 

jgdyer

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Thanks, Valveman ...

It is set at 50/70 ...

My concerns are that perhaps: a) The smaller 3/4" leg to the tank and the tank location below the supply line both affect drawdown, and b) The pressure switch and gauge above the tank affects calibration ..

I plan to re-plumb with 1" ... drop straight down and approach the tank from behind ( reducing ells and branches ) ... and set a manifold with gauge, switch and drain valve on the front side straight out from the base ...

I cannot decide whether to tee into the supply at the present tap-in point or replace the ell just to the right with a tee and drop from there ... My concern is that I might get too much hydraulic velocity down the tank leg ... But I don't know enough about hydraulic behavior to guess ...

And, while at it, I suppose I ought to go with more than a 20 gallon tank ...

A tank size calculator on a vendor's website advised an 85 gallon tank ...

Gee, what a coincidence it's the biggest one they make in the residential line ...

Do you think I can get away with something smaller? ( two bedroom, two bath, two people )

Also, what's the buzz on Wellmate composite tanks?

Thanks!
 

Valveman

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Better make sure your guage will go to zero when the pump is off and the tank is empty. It is common for a guage to be reading 20 PSI higher than it should, so it won't go lower than 20 even when the tank is empty. If you really have 50/70, it should knock you down in the shower. If you really have 50/70 at the tank, then check the pressure at a sink or shower head, because you must have some restriction after the tank. The water goes right past the tank to the shower, so I don't think your plumbing is a problem.

And don't get a bigger tank. That is the old way of doing things. I only use a 80 gallon tank for a city of 40,000 people. I use a 4.4 gallon tank for a single house, but of course both size systems need a CSV to be able to use such small tanks. A bigger tank just means your pressure stays lower for longer periods of time. Wellmate is OK, but you don't need a new tank.
 

jgdyer

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On the topic of a CSV ... What happens if the CSV were installed in the machine space in my photo ( upstairs ) and I use my hydrants downstairs ( which are plumbed in before the CSV and pressure tank ) .. My well vault floods .. Which I am concerned might affect CSV operation and longevity ...
 

Valveman

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Most CSV's can be submerged with a little preperation. We have some that are submerged in the well for certain applications. The CSV has to go before any water lines tee off to hydrants or anything.
 
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