Pressure tank outlet size? Pressure tank sizing for trickle irrigation scenario?

[cdherman]

I have bought into the idea of the CSV and smaller pressure tank in the house to get rid of freezing problems in the well.

I see smaller pressure tanks with 3/4" inlets, 1" inlet, and I found one 6 gallon with a 1 1/4" inlet. I presume that larger means better flow and a quicker depletion of the water in the tank and subsequent turning on of the pump which then in turn will provide a constant 50 psi irregardless of flow, so long as its over 1 gpm.

Is 3/4" enough for a 4.5 gallon pressure tank?

Second question -- my mother tends to trickle irrigate garden plots. Probably at rates like 0.25 gallon per minute. A small pressure tank, like the 4.5 gal only has 1.5 gallon water. This could result in the pump cycling every 6 minutes, if I understand things correctly. Should this possible use scenario cause me to consider a somewhat larger pressure tank to avoid cycling the pump too much? In my other post, someone mentions that too large a tank will result in a delay in the pump coming on. While that is perhaps a bit annoying, it would not damage anything.

 

[Valveman]

Even with a small pressure tank there is no flow rate you can use that will hurt the pump when controlled by a CSV. As you stated, even a 0.25 GPM flow will only cause the pump to come on every 6 minutes. It will then take about 1 minute for the CSV to refill the tank and the pump shut off. A cycle every 7 minutes is only 205 per 24 hour day. That is less than the 300 max cycles a 1HP or smaller pump is designed to handle.

However, 205 is still a lot of cycles per day. We always recommend a larger tank when flow rates of less than 1 GPM are used or leaking for long periods of time, like with drip systems. Setting the CSV closer to the off setting can create 1 or 2 minute fill times for any size of tank. So, you can use as large a tank as you want. An 86 gallon size tank holds 20 gallons of water and would let a drip run at 0.25 GPM for 80 minutes. A cycle every hour and a half reduces the total to 16 from 205. However, for other uses the large tank means you will be at the low end of the 40/60 pressure switch for longer periods of time. With a 3 GPM shower running the first 7 minutes will be with pressure decreasing from 60 all the way down to 40. As soon as the pump comes on the tank will refill to 58, and the rest of the shower will be at a strong constant 58 PSI from the CSV.

With the small tank the pump cycles more for flows less than 1 GPM, but the pump is on and the pressure is at a strong constant 50 PSI before you get the temp adjusted. A 20 gallon size tank, that holds 5 gallons of water is a good compromise.

 

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[cdherman]

Even with a small pressure tank there is no flow rate you can use that will hurt the pump when controlled by a CSV. As you stated, even a 0.25 GPM flow will only cause the pump to come on every 6 minutes. It will then take about 1 minute for the CSV to refill the tank and the pump shut off. A cycle every 7 minutes is only 205 per 24 hour day. That is less than the 300 max cycles a 1HP or smaller pump is designed to handle.

However, 205 is still a lot of cycles per day. We always recommend a larger tank when flow rates of less than 1 GPM are used or leaking for long periods of time, like with drip systems. Setting the CSV closer to the off setting can create 1 or 2 minute fill times for any size of tank. So, you can use as large a tank as you want. An 86 gallon size tank holds 20 gallons of water and would let a drip run at 0.25 GPM for 80 minutes. A cycle every hour and a half reduces the total to 16 from 205. However, for other uses the large tank means you will be at the low end of the 40/60 pressure switch for longer periods of time. With a 3 GPM shower running the first 7 minutes will be with pressure decreasing from 60 all the way down to 40. As soon as the pump comes on the tank will refill to 58, and the rest of the shower will be at a strong constant 58 PSI from the CSV.

With the small tank the pump cycles more for flows less than 1 GPM, but the pump is on and the pressure is at a strong constant 50 PSI before you get the temp adjusted. A 20 gallon size tank, that holds 5 gallons of water is a good compromise.

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Hey Valveman. I have another question. I see a check valve in a lot or perhaps all of your diagrams. That got me researching and I found a post from YOU of all people from like 2009 where you come out against additional check valves IF the submersible pump has one already built it. Does that advice still apply? Or have you changed your mind? You gave pretty decent explanation back then!

 

[Valveman]

Yes. Only one check valve on the pump the same as the diagrams above.

 

[cdherman]

So are you saying one check valve just above the pump PLUS the built in check valve in the pump?

 

[Reach4]

So are you saying one check valve just above the pump PLUS the built in check valve in the pump?

That would be OK.