Cistern pump and pressure tank setup

[jbarilwalker]

Hi all, new member with some questions.

I'm designing a water system where I will be filling a 1500 gallon underground cistern gravity fed from a spring for part of the year and from a low production shallow well for the rest of the year then pumping from the cistern to my house. Getting water from the spring to the cistern is no problem, and getting water from the shallow well to the cistern for the rest of the year is no problem, either; that can be done with a small sump pump that slowly fills the cistern and a float switch.

I like to think that I'm fairly smart, but it's good to ask questions when you aren't sure of something. With that being said, I'm trying to decide on the best pump and pressure tank set up before I move forward.

My cistern is buried around 10' from an insulated utility shed with an electrical service panel. On the advice of a professional plumber (not so sure about that now) I buried 1" municipal waterline from the shed to the house. My original plan was to use a large jet pump and pressure tank in the shed to send water up to the house. Many people use this kind of setup in our area, I know it's probably not the "best" way to do things, but that's what I modelled my plans after. Based on my calculations, I would need a 2hp jet pump and something like an Amtrol Well-X-Trol pressure tank which can hold high psi to make this work.

I'm wondering if there is a better way. I realize now that it would have been much, much better if I had buried 1.25" or even 1.5" municipal waterline up to the house (less friction loss). Perhaps using a submersible pump will be better for me (more efficient pump, longer life etc). Having the pressure tank in the house, not in the utility shed might also have been a better choice (trying to avoid this situation because then I will need to run extra wire between the pump shed and the house for the pressure switch).

Heres the numbers I'm working with, any advice on what YOU would do for an efficient, long lasting setup? This is new construction, DIY everything, so whatever I do now I will be living with for many years.

Desired flow rate: 10gpm
Total Pipe Length: 220'
Pipe Diameter: 1" municipal (0.863" ID, C factor of 150)
total vertical height from cistern to house: 40'
pumping depth from cistern to utility shed: 5' (only really applicable if I use a jet pump)

I've calculated that the total pump head required will be around 220' - friction loss from the marginal 1" municipal waterline is very significant. Burying a second, larger pipe is an option if it will really make my situation better. I would still prefer to keep the pressure tank in the utility shed if at all possible since I've already started doing things this way.

 

[Reach4]

Pipe Diameter: 1" municipal (0.863" ID, C factor of 150)

I am not familiar with that kind of pipe.

http://www.pressure-drop.com/Online-Calculator/ is good for figuring the dynamic pressure drop in the pipe to the house.

You seem to have thought about all of the right things. A house would usually be good with a 7 gpm pump, unless you have some special loads.

 

[Sponsor]

 

[Valveman]

I think you are over figuring a bit. The 220' of pipe is horizontal, so all you have is about 5 PSI (11' of head) friction loss, plus the 45' lift, and another 50 PSI (115' of head) totaling 171' of head or (74 PSI) at 10 GPM. That would only take a 10 GPM, 1/2HP submersible, like a 10GS05 Goulds. Or you can use a multistage booster pump like a 10GB07 Goulds. You would need more horsepower and a multi-stage jet pump to make that kind of pressure. Pumps are more efficient pushing than sucking, so it takes a larger jet or booster to do what a smaller sub would do. With a jet pump you would need about a 1.5HP , like a Goulds HSJ15N.

Any of those will work with a PK1A control kit, You would need the 10 gallon size tank and a 60/80 pressure switch so the CSV could deliver 74 PSI constant up the hill. Also the friction loss is figured with 10 GPM flow, and with the CSV in the PK1A the flow will only be as much as is being used. When you are using a 3 GPM shower and the CSV is making the pump produce only 3 GPM at 74 PSI constant, there will be no friction loss and you will actually have 5 PSI more than we are figuring at the house.

 

[Reach4]

I did this calculation. I put the roughness at 0.1 mm, because I do not know how to convert from C factor. I used 240 ft for the length to compensate a bit for fittings and whatever.

Flow medium: Water 20 C / liquid
Volume flow:: 10 gal/min
Weight density: 998.206 kg/m3
Dynamic Viscosity: 1001.61 10-6 kg/ms
Element of pipe: circular
Dimensions of element: Diameter of pipe D: 0.863 in.
Length of pipe L: 240 ft.
Velocity of flow: 5.48 ft./s
Reynolds number: 36521
Velocity of flow 2: -
Reynolds number 2: -
Flow: turbulent
Absolute roughness: .1 mm
Pipe friction number: 0.03
Resistance coefficient: 106.96
Resist.coeff.branching pipe: -
Press.drop branch.pipe: -
Pressure drop: 3116.12 lbw./sq.ft.
21.64 psi​

So the altitude difference will be constant. When you go up to 10 gpm usage (a very high rate for a house), the pressure will drop about 22 psi. Not terrible. Not great. I re-ran for 5 gpm, and there was only 6 psi drop.

Raising the roughness to 2 mm and still at 5 gpm, I got a dynamic drop of 16.4 psi. Click on the book icon on the roughness number, and it will tell you the roughness of various kinds of pipe.

If you put the pressure tank and pressure switch inside, that dynamic drop mostly disappears in effect.

 

[Valveman]

I guess that is closer to the 3/4" pipe in my book. If there is 22 PSI instead of 5 PSI loss at 10 GPM, you will need to add 17 PSI to the numbers I gave earlier. That dynamic drop will still be there no matter where you put the pressure tank. But tank and switch after the dynamic loss you can set it 22 PSI lower than if it was at the beginning of the loss.

 

[jbarilwalker]

Thanks for the prompt replies and advice. Overcomplicating things is typical for me, thanks for simplifying it a bit.

I re-ran the numbers a multitude of ways; I crossed referenced the calculator above and pipe roughness for my 1" HDPE municipal pipe is = to 0.0015". Let's say I do as suggested and drop to 7gpm flow, probably more than adequate for our needs (I tend to overdo things). I end up with an 8.13psi drop, or a little under 19' of head from the run to the house. Add on my 45' of lift to get up the hill to the house, plus 50psi/117' of head needed once I'm up there for end use. Now it's all starting to make more sense.

Few more questions for you guys when you have a chance.

Lets say I live in a very rural area (I do) and the closest Goulds dealer is over 5hrs away. Other quality pumps can surely be sourced closer to me. I know I'm overcomplicating matters when I think it through but am wondering if you could simplify pump selection for me. In my case the numbers I'm concerned with are a total head of approx 180' and a flow of 7gpm. If I cross reference any submersible or jet pumps I can find locally, as long as I'm within those numbers I should be good to go - correct? I have read about performance curves and have a bit of a grasp on what parameters I want to stay within.

Second question, using a CSV makes sense and is a possibility, but if I want to keep this simple and stick the pressure tank in the utility shed close to the cistern and pressurize the system up to the house using a conventional pressure tank/switch with parts I can buy easily at my local suppliers, I would simply want to select a large enough pressure tank so I have ample drawdown capacity since I'm using such pressure in the tank, ensure the tank can handle the high pressure needed and select a suitable pressure switch. In this case I would probably go up to a 70/90 pressure switch.

What happens if I put a yard hydrant (or two) along the line between the pressure tank and the house. Lets say I have one yard hydrant close to the utility shed, and another halfway up to the house. If they are not subject to as much vertical head loss and as much friction loss in the pipe, the pressure coming out of those yard hydrants will be significantly different from what's in the house, could this plan be problematic? Possibly warrant the need for a pressure reducer on the yard hydrants?

I'm very grateful of the help, I've got an inquisitive mind and like to learn as much as I can when I do something!

 

[Reach4]

I re-ran the numbers a multitude of ways; I crossed referenced the calculator above and pipe roughness for my 1" HDPE municipal pipe is = to 0.0015".

I was looking what you get when you click the book icon. A snip of most of that is attached. I had looked for such a conversion/cross-reference, and did not find one.

You should be fine, as long as your expectations are reasonable.

 

[Valveman]

Using a submersible any 10 GPM, 1/2HP pump will do that job. Some are made a little better than others but not that much difference. With a multi-stage booster it will take 3/4HP, and still at least 1.5HP with a jet pump. Your water comes from the pump, not the tank. The tanks only purpose is to limit the number of on/off cycles. When you have a Cycle Stop Valve to stop the cycling, you don't need much of a tank. But otherwise the CSV works with the conventional pressure tank/pressure switch and parts.

The higher the pressure setting the less water a pressure tank holds. At 70/90 I would use at least a 1o gallon size conventional tank as comes with a PK1A kit. But without the CSV, it would take a 36 or a 44 gallon size tank to get the minimum one minute of run time. Without a CSV two minutes of run time which requires twice that size tank would be best, and still not as good as the CSV and small tank.

 

[jbarilwalker]

Thank you both very kindly. Reach4, I found another couple of conversion charts online that gave the pipe roughness value of 0.0015 so I stuck with that.
Valveman, I might just order the CSV and use it with a smaller pressure tank here. Reason I wouldn't order the entire system is that shipping to western Canada is probably fairly expensive and given the world "situation" at the moment shipping is slower than usual.

 

[Valveman]

Shipping a tank is expensive, even a small tank. You can get the PK1ALT, which the LT means less tank. The shipping will be much less expensive but everything you need is still in the kit except for the pressure tank, which can be a locally sourced 4.5 gallon or larger tank.