Pipe Size From Well To Pressure Tank

[madisonplumdesign]

Hi all,

I'm designing the plumbing for a vet. clinic addition. The current well has a 3/4 HP, 10 gpm pump. The pressure tank is a Well-Ex-Troll 250. The pipe size from the well to the pressure tank is 1".
After counting the fixture units and gpm for the new and existing building, I'm at 44 gpm for the total flow. In my oppinion based on the number of employees, the worst case scenerio would be 20 to 25 gpm being used at once. I actually have two questions...

1) When sizing this well pump, would I size it for total flow? What I mean is, would I need a 44 gpm pump?

2) How concerned should I be with the 1" line coming from the well? Per the WI code, water velocity needs to be 8 FPS or less within the building. I've been told by plumbers that this doesn't apply to the pipe coming from the well. Also, what is the largest pump you would comfortably suggest using with that 1" line?

Thanks in advance for your suggestions!

Shane

[Bob NH]

You need to get a good idea of the demand for the clinic. Not something about adding up fixtures, but about how many real gallons per minute you are going to need.

Determine the design demand (which should be right up your alley, given your id name here) for the following:

Total demand in any 1 minute.
Total demand in any 3 minutes.
Total demand in any 10 minutes.
Total demand in any 30 minutes.
Total demand in any 60 minutes.

Then someone can figure out how much pump capacity (GPM) and pressurized storage you will need for the clinic.

You also need to know how much the well (not the pump) will produce in 30 minutes, and 1, 2, 4, 8, and 24 hours.

With that information, you (or someone) can design a system and select components.

The pump has to match the capacity of the well, although you can overpump for a short time. What the well or pump can't produce, you must deliver from storage.

That is why the total demand over various time intervals is important.

Ordinarily, the pipe size from a submersible in a well is equal to the size of the discharge of the pump. If it is a jet or centrifugal pump, it is common to upsize one pipe size because the pump inlets and outlets are often undersize because of casing design constraints.

A good starting point for demand estimate is to find the total daily demand, and take maybe 25% of that for the peak hour.

[speedbump]

That 1" pipe is about maxed out at 25 gpm. There is already a lot of friction loss in the 1" at that flow, but more would be practically impossible.

bob...

[madisonplumdesign]

Thanks for your help guys. I sincerely appreciate the info.

Shane

[John_NC]

You may be fine with a 1" pipe on a 10gpm pump however today's pumps are usually 1 1/4 " for 10gpm - 20gpm capacity. It's fairly common for installers to reduce drop pipe size on these to 1" but I'm not a fan of introducing any unnecessary restrictions or friction loss if it can be avioded. Simple rule of thumb, I would use a pipe that fits the intended output size.

Also, from my research, pumps are capable of pumping up to around 40% more gpm than they are rated in the best case scenarios. IE, you have well production = to the pump's maximum output. So, a 10 gpm pump could deliver 14 gpm if your TDH is less than 150' or so.

I'm not an expert so feel free to take this free advice for what it's worth. I'm just sharing the knowledge I have learned while researching my own pump sizing for a particularly challenging application.

John

[speedbump]

One of the reasons we drop down to 1" from 1-1/4" is to add a little friction to keep the pump from pulling over max amps when people run them to fill ponds etc. When you run a pump open discharge, the amps can go over the motors rated value. This overheats the motor and will eventually trip the overload protector. This extra heat is just one more thing to shorten a motors life expectancy.

bob...