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# Sprinkler piping

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• This topic has 3 replies, 4 voices, and was last updated 22 years ago by TheLocalPlumber.
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• #272980
MasterPlumbers
Keymaster

I am looking to install a lawn sprinkler system. The contractors are requesting a 1″ water supply
to feed the system. It would be plumbed from just above the water meter. The main water supply is 1 1/4″ but is reduced to 3/4″ as it passes through the water meter.

Wouldn’t the 3/4″ restriction through the water meter eliminate any benefit of having a 1″ supply to the lawn sprinkler?

• #286666
hj
Participant

Some, but not as much as the pressure loss running the system through a 3/4″ pipe.

• #286667
SylvanLMP
Participant

Steve the 1″ pipe could be sized by the volume required. You see a lot of “plumbers” confuse pressure with volume. If you have a 11/4 line with 50 PSI and install a 3/4″ in line off of it YOU just lowered the volume BUT not the pressure.

This is why some “plumbers” should never get involved in sprinkler work as they have no conception of the K factor and other parts of a system that must be taken into account.

The only aspect that should concern you about this reduction from 11/4 to 3/4 is the velocity created which on copper tubing can cause severe erosion problems.

What your sprinkler contractor should do is find the orifice of each head and then find the total area of the combined area.
Here this may help if you have an 11/4 @ 8 FPS (velocity) you would have a flow rate 3of 1.25 GPM now that it is cut down to 3/4 “your flow rate would be 5.83 GPM and here lies the problem NOT THE PRESSURE as your pressure would remain constant UNLESS you went from small piping to larger piping then under a flowing condition your pressure would drop considerably.

I am sure you can get a larger meter installed OR increase the 3/4 outlet to a larger size and have the plumber calculate the flow with just knowing the pipe sizing and the available pressure THEN he/she can work out your exact requirements.

If you have a local plumbing trade school near by ANY 2nd year apprentice can work out this formula. Good luck

• #286668
TheLocalPlumber
Participant

Steve,
Your main water service starts at the meter, hence, your main water service is 3/4.
Increasing the 3/4 to 1″ for a sprinkler system serves no usefull purpose. Good Luck.
Bill
The Local Plumber
Tustin, California
http://www.thelocalplumber.com