# Friction loss in reverse: Small pipe to Large.

Discussion in 'Pumps and Tanks Well Forum & Blog. Water is life.' started by stormlight, Sep 13, 2018.

1. ### stormlightNew Member

Joined:
Sep 11, 2018
Location:
CA
I understand the concept of friction when going from a larger pipe diameter to small. However, what happens in reverse?

For example, I have a well pump that has a 1 inch output and I have 1 1/4 sprinkler lines coming of that 1 inch pipe.

Since the well pump has 1 inch output does that mean I will never get to use the extra friction room that a 1 1/4 pipe gives over a 1 inch pipe?

Basically it goes: Suction up the well water via the pump at 1 1/4. Then go through the pump and then discharge out of the pump orriface at 1 inch. It gets imediatley converted to a 1 1/4 pvc going out to various devices. Is the 1 1/4 pipe useless after the 1 inch discharge?

Thanks all

2. ### Reach4Well-Known Member

Joined:
Sep 25, 2013
Location:
IL
No. The pressure drops add. The one inch section has a drop. Then the 1-1/4 section has a drop. It's not like road traffic where the slowest section determines the throughput.

4. ### stormlightNew Member

Joined:
Sep 11, 2018
Location:
CA
So if im understanding since there is less then an inch of 1 inch pipe in this run (it gets converted from the 1 inch output to 1 1/4 pipe right at the pump) I can pretty much ignore the friction from the 1 inch pipe since its so small.

5. ### valvemanCary AustinStaff Member

Joined:
Mar 15, 2006
Occupation:
Pump Controls Technician
Location:
Lubbock, Texas
No. As Reach said each leg adds additional friction loss. Determine the friction loss in the length of 1" pipe. Determine the friction loss in the actual length of 1 1/4" pipe, and add the two together. You would have even more friction loss if all the pipe was 1".

6. ### stormlightNew Member

Joined:
Sep 11, 2018
Location:
CA
What I was saying is that the total length of the one inch pipe in this run is less then .5 inches. According to the friction calculator 1 foot of 1 inch sSCH 40 pipe has .31 of pressure loss. If i divide .31/12 that is not even measurable for me. What I was most concerned was for that tiny .5 inch run of 1 inch pipe to be the limiter in the entire run of all my 100 foot four zones that have 1 1/4 pipe size.

It looks like its not and i just need to ad .02 (.32/12 inch) to my friction.

7. ### valvemanCary AustinStaff Member

Joined:
Mar 15, 2006
Occupation:
Pump Controls Technician
Location:
Lubbock, Texas
That is correct. You can push a lot of water through a short piece of small pipe without much friction loss. But it you have hundreds of feet of small pipe the friction loss adds up quickly. We can easily push 25 GPM through a short 1" CSV, but you want to go back up to 1 1/4 or larger pipe after that or you will start losing pressure.

8. ### Reach4Well-Known Member

Joined:
Sep 25, 2013
Location:
IL
Maybe you chose too high of a flow. Your pump is not going to put out more than about 10 gpm I suspect.

You might try this calculator: http://www.pressure-drop.com/Online-Calculator/ Maybe use 0.1 mm for the roughness.

It has choices of things other than straight runs, such as change of section, although I have not played with those.

Last edited: Sep 13, 2018