Tank pressure changes

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Anna W

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For some reason the plumber who installed our 40 gallon pressure tank originally set the cut in/out pressures at 30/50 even though the switch is a 40/60. Our pressure has always been low, and after reading a million posts when we recently had a lightning strike, we asked the well guy who fixed the outside box to up our pressure tank to a 40/60 cut in/out. Since the air pressure was set for the 30/50 (27 or so PSI), we added air to the tank (air in tank now at 36.5 PSI) to 3 PSI below the higher cut in. The well guy was not very helpful beyond replacing the switch box, so I just wonder why the initial setting was low (30/50) when the switch was rated 40/60? Why do other posts say a 40/60 wears out a pump more than a 30/50 when the pressure differential for the pump going on and off is the same (ie, 20 PSI)? My hub was freaked out to add air to the tank (which we did) but I wonder why it matters if the air pressure is LOWER, if the pump is going to kick on at a higher cut in anyway (ie, if we had left the air pressure at the old 28 PSI) (this is just for my info/ general knowledge)? Our pressure is better now, but I don't want to cause our pump stress as we have a deep well, and seem to draw water issues to us like magnets. Thanks for your help/comments. aw
 

Reach4

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The drawdown for the pressure tank is a little more for 30/50 vs 40/60. On the other hand, the pump will produce a little lower GPM at the higher pressure.

What is the minimum time the pump runs?

Is this a submersible or jet pump?
 

Anna W

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The pump is submersed in the ground/well. I am not sure if when you say how long does the pump run, do you mean how long does it take b/t the time the cut in goes and the cut out goes off? (I am a layperson, sorry for ignorance...learning.) I forgot about the drawdown, I saw a chart that showed the different specs.... will look that up again.
 

Valveman

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With the proper air charge a 40 gallon tank will hold about 12 gallons at 40/60. But with low air pressure it will only hold about 10 gallons and you are over-stretching the tank bladder to do this. However, low air pressure in the tank is the only way to guarantee a few gallons of water stored for power outages. There is always a tradeoff.

The longer it takes to fill and/or drain the tank, the fewer cycles the pump will have, which is better of course.
 

Reach4

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The pump is submersed in the ground/well. I am not sure if when you say how long does the pump run, do you mean how long does it take b/t the time the cut in goes and the cut out goes off? (I am a layperson, sorry for ignorance...learning.) I forgot about the drawdown, I saw a chart that showed the different specs.... will look that up again.
(I had written this earlier, but neglected to post)
It is good that your pump is submersed.
Yes, the time between cut in and cut out. You want that to be at least a minute. If the pressure tank is large compared to the pump flow, the run is longer. A longer run is better. A 40 gallon pressure tank would be good for about a 7 GPM pump-- maybe a pump pumping 10 GPM.

For a submersible pump, if the cut-in is 40 PSI, a 38 PSI precharge is usually suggested. That way the expansion of the diaphragm in the tank is less than if the 36.5 PSI precharge is used. A jet pump would call for a lower precharge, because they are less responsive.

The 40-60 vs PSI pressure switch dropeed to 30-50 PSI is fine. Raising back to 40-60 is fine too, presuming the pump is capable. I have my 30/50 raised to about 38/58. It is not bad for the pump as long as the water pressure was still rising nicely as it cuts off.
 

Anna W

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Hello and thanks for the responses, Reach4 and valveman. I see I should add some more air, and check how long the pump runs when filling. More pending those actions.... af
 

Anna W

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OK, back. Cut in goes on exactly at 40, and cut off at 60 PSI (looked while filling washing machine... did this x 2). Each 'fill' only took 55 seconds. Here's what specs I could find from paperwork (when well dropped and recent std control box replaced): 2 HP, 7 GPM F&W Pump, 2 HP Standard control box (original was 'deluxe'). Feedback (I am trying NOT to project what you are going to say here....)? Thx.
 
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