# changing water pump outlet connection from 1.25-inch to 1-inch, how to calculation flow and pressure

Submersible well pump with 1.25-inch outlet connection I've changed to 1-inch how to calculation the flow and the pressure?

Here's the submersible well pump details with standard 1.25-inch outlet connection.

Q = 100 L/min

How to find out the Q and the head of the same pump with 1-inch outlet connection?

• This depends on more than the connection itself. It also depends on the developed length and diameter of the pipe it's connected to. If you leave it open to the atmosphere, just pumping away, you won't likely see any difference in pump performance, whereas over 1km of 1" pipe, you might find there's a huge difference. – Hari Ganti Feb 15 '18 at 1:24

Actually, the pressure will not change. Pressure is resistance at the end point, where ever that may be measured (in your case, the holding tank setup). The pump doesn't create pressure. Once the water pressurizes, the intake water will stagnate, not continuing through the pump.

To not go too deep, I'd say, if you have a factory flow rate of 100L/m with a full size outlet of 1 1/4", it's probably safe to say that reducing the pipe size about 20% to 1" pipe would give you a flow rate of around 80L/m.

Btw, great question.

• 1 1/4" to 1" isn't a 20% reduction, it's ~36% reduction (the cross section area is what affects flow). – fixer1234 Apr 27 '18 at 18:57

You'll have to look into bernoulli's equation which esentially describes how fluids work in a system. You'll want to focus on the Head loss Portion of that equation. Head loss is what your pump has to overcome to push water through the system. I can tell you that by reducing your pipe size you will increase your system head, which will require your pump to work harder. Whether or not your pump will actually overcome this increase in head would have to be determined by using bernoulli's equation and comparing it to your pump's performance curve. Hope that helps.

First off, the largest residential submersible pumps (5HP +/-) will not typically have 25 GPM flow at a total system head of 800' or so, so I think you might be a bit misinformed as to the capabilities of your pump. A 5 HP pump I found showed about 4GPM +/- at 800' of head. At that flow 1" pipe will be no problem.

Second, pump aside, 100L/min will flow way too fast through 1" pipe, so assume you will not be getting any where near that even if you could.

A typical way to identify flow from a pump through a system is to calculate an equivalent head, then reference the pump data to find the flow at that head (PSI instead of ft/m).

That is

actual head + head from pipe losses (typically PSI per 100' at given flow) + head from fitting & valve losses + target output pressure.

Say you had a bushing and fittings that added 2 PSI and 700'+100' of 1" pipe that adds 3.5 PSI per 100' @ 15 GPM + target output pressure of 50 PSI , you would have an equivalent head of about 875'. Then you could reference the expected output on the pump chart at 875' of head and select a pump based on the total system head pressure.

Although again, to get the flows you are talking at the head you are talking would be a three phase higher HP (for residential) pump which would be rare.

Fluid dynamics is actually rather complex to predict. This is why manufacturers use test and measure methods and then let you extrapolate on the data based on your total calculated head.