Pump tank pressure
#1
12-18-12, 05:06 PM
Pump tank pressure
I have read through and even helped on several threads concerning the proper pressure on holding tanks for a well pump. I seem to be having a problem of my own that others may have experienced.
In my weekend rental cabin I have the holding tank. Cut in is 30 out 50. 42 gallon blue tank. I turned off the breaker to the pump and drained the system. Checked the pressure on the top of the tank and it was 18 lbs. Pumped it up to 28 psi and turned on the system. Pressure in the showers seemed to be much better.
However, there doesn't seem to be any water in the tank. It is light, and I can tilt it slightly with little pressure. Is this normal? Should there be gallons of water in the tank below the bladder, or is the extra pressure keeping it down?
Puzzled at best. Thanks for the insight.
In my weekend rental cabin I have the holding tank. Cut in is 30 out 50. 42 gallon blue tank. I turned off the breaker to the pump and drained the system. Checked the pressure on the top of the tank and it was 18 lbs. Pumped it up to 28 psi and turned on the system. Pressure in the showers seemed to be much better.
However, there doesn't seem to be any water in the tank. It is light, and I can tilt it slightly with little pressure. Is this normal? Should there be gallons of water in the tank below the bladder, or is the extra pressure keeping it down?
Puzzled at best. Thanks for the insight.
#3
12-18-12, 06:24 PM
Not 100%, but had one at the location and one from my truck console. Do you think the pressure is too high or too low with the situation as it is??
#4
12-18-12, 06:31 PM
Join Date: Jan 2008
Location: Southeastern Pennsylvania
Posts: 3,104
Received 93 Upvotes
on
85 Posts
Hi chandler –
I am an absolute newbie so you’ll have to wait for the pros. But I know a Gould V140 tank is about 45 gals and has a drawdown of about 14 gals at the 30-50 psi setting. A gal of water weighs about 8.3 pounds.
So it seems to me your 40 gal tank pumped up to 50 psi should contain at least… let’s just say 10 gals of water? And thus should be weigh at least 10x8.3 pounds? But I guess I sure could be wrong, just playing an expert!LOL
Will be interesting to hear what the pros say.
Good luck!
I am an absolute newbie so you’ll have to wait for the pros. But I know a Gould V140 tank is about 45 gals and has a drawdown of about 14 gals at the 30-50 psi setting. A gal of water weighs about 8.3 pounds.
So it seems to me your 40 gal tank pumped up to 50 psi should contain at least… let’s just say 10 gals of water? And thus should be weigh at least 10x8.3 pounds? But I guess I sure could be wrong, just playing an expert!LOL
Will be interesting to hear what the pros say.
Good luck!
#5
12-18-12, 06:39 PM
Super Moderator
Chandler when my tank kicks on it working off direct draw until it builds up psi. The tank is as far as empty when the pump is running.
After the pump kicks off then it has some weight to it. But not so much weight that if you assumed the whole tank was full. Probably in the bladder tanks not even 1/3 of the tank is full of water after kick off.
hope this helps....
After the pump kicks off then it has some weight to it. But not so much weight that if you assumed the whole tank was full. Probably in the bladder tanks not even 1/3 of the tank is full of water after kick off.
hope this helps....
#6
12-19-12, 05:17 AM
OK, so almost total drawdown as long as the pump is working. Then when demand is at idle, pump puts 28 pounds of water/pressure in the tank. Makes sense. I was running the water when I felt the tank's weight. Since I have adequate water pressure I will let sleeping dogs lie.....or chickens, either way. Thanks, guys.
#7
12-19-12, 05:27 AM
Super Moderator
Yeah...I have a 36 gallon tank. I believe it takes 9 gallons to drain before the pump kicks on. Then the tank is pretty empty.
If you had too much air in the tank ,you would get a brief , no water situation just before the pump kicks on. Thats from pump lag.
If you had too much air in the tank ,you would get a brief , no water situation just before the pump kicks on. Thats from pump lag.
#8
12-19-12, 06:58 AM
OK, one more question. I have read differing opinions on this. Does it really matter where the tank is in relation to the pump? Both my house and cabin tanks are inside the house, probably 100' from the pump. I figure pressure is pressure. Am I wrong?
I certainly hope not, because I just had my guys pour concrete foundations around the well head and build cute little houses around them, and there is no room for a tank in either one, without making a front porch on them
I certainly hope not, because I just had my guys pour concrete foundations around the well head and build cute little houses around them, and there is no room for a tank in either one, without making a front porch on them
#9
12-19-12, 07:47 AM
Member
Join Date: Nov 2012
Location: Canada
Posts: 298
Upvotes: 0
Received 0 Upvotes
on
0 Posts
.
Some friction loss is simply unavoidable.....your layout is fine.
If you installed the pump inside it would still have to move the water the same distance.
If you move the tank to the pump location then you will likely be worse off.
It's better to have the tank in the house as the initial supply is provided by the draw-down.
That flow and pressure is less than the pump......so the shorter outlet run on the tank is ideal.
.
Some friction loss is simply unavoidable.....your layout is fine.
If you installed the pump inside it would still have to move the water the same distance.
If you move the tank to the pump location then you will likely be worse off.
It's better to have the tank in the house as the initial supply is provided by the draw-down.
That flow and pressure is less than the pump......so the shorter outlet run on the tank is ideal.
.
#10
12-19-12, 09:23 AM
Just to put a finer point on it...I believe for the tank to be completely empty the supply side pressure would need to be 28psi or below (using your numbers).
Is there a way to calculate tank water capacity based on the delta pressure?
Is there a way to calculate tank water capacity based on the delta pressure?
#11
12-19-12, 10:57 AM
Member
Join Date: Nov 2012
Location: Canada
Posts: 298
Upvotes: 0
Received 0 Upvotes
on
0 Posts
.
The formula to calculate the drawdown volume on a (captive-air) pressure tank is.....
(P1 / P2 – P1 / P3) x V
P1 = the pre-charge pressure
P2 = the cut-in pressure
P3 = the cut-out pressure
V = total tank volume
( +14.7 psi at sea level altitude )
For Chandlers' setup....
(28 + 14.7) divided by (30 + 14.7) minus (28 + 14.7) divided by (50 + 14.7) times 42
Or....... (42.7 / 44.7) – (42.7 / 64.7) x 42
Therefore......the drawdown volume is...... 0.295 x 42 = 12.39 gallons
.
The formula to calculate the drawdown volume on a (captive-air) pressure tank is.....
(P1 / P2 – P1 / P3) x V
P1 = the pre-charge pressure
P2 = the cut-in pressure
P3 = the cut-out pressure
V = total tank volume
( +14.7 psi at sea level altitude )
For Chandlers' setup....
(28 + 14.7) divided by (30 + 14.7) minus (28 + 14.7) divided by (50 + 14.7) times 42
Or....... (42.7 / 44.7) – (42.7 / 64.7) x 42
Therefore......the drawdown volume is...... 0.295 x 42 = 12.39 gallons
.
Thanks guys!! Always a treat to get answers here when you're supposed to know this stuff.
#13
12-19-12, 11:12 AM
Super Moderator
The formula to calculate the drawdown volume on a (captive-air) pressure tank is.....
(P1 / P2 – P1 / P3) x V
(P1 / P2 – P1 / P3) x V
Yeah...I have a 36 gallon tank. I believe it takes 9 gallons to drain before the pump kicks on. Then the tank is pretty empty.
Funny , I did the calculation and I got 9.36 for mine...
Its good to know the math to figure, but I just filled a bucket when I tested my capacity until the pump cut in, and got 9 gallons....LOL
The .36 gallons is whats left in the tank so the bladder does not collapse on itself....hence the 2 psi lower then cut in.
