- SPRINKLER TALK FORUM - You Got Questions, We've Got Answers »
- Help Choosing The Right Sprinkler Products »
- Miscellaneous Items »

Our sprinkler system uses lake for it's water supply. The lake has gone down so far that we have extended our suction pipe over 100 ft. to reach the water. Is this the reason we've lost pressure to our sprinker heads? We were able to run 6-7 heads at a time, now we are only able to run (3) heads at a time. Thanks for your input.

1) Depending on the diameter of your suction pipe and your flow rate, your additional pressure loss due to friction could be high. For example, if you are using 1" copper pipe at a flow rate of 10 gal/min, 100 ft of pipe would add an additional 3.7 psi of pressure loss. See this link for some great friction loss tables: http://www.irrigationtutorials.com/sprinkler09.htm

Please note that pipe friction is a beast, if your pipe has significant build up, or lots of fittings, your friction loss could be much greater depending on flow rate.

2) The formula for the pressure loss due to the decrease in lake level is:

(Change in Pressure) = (density of water) * (gravity) * (change in suction point elevation)

Given that you are on the plant earth and the water you are using is of normal density (no nuclear power plants nearby), plugging in the constants gives you:

P(psi) = 0.0362 * height (inches) or

P(psi) = 0.434 * height (ft)

Therefore if you lost 10 ft of elevation at your suction point, you would have an additional 4.3 psi of pressure loss.

If after you have done the math and you find that you still have plenty of pressure available in your system, then I would suggest you start to look for some sort of clog or flow restriction in your system. Clean your filter, etc....

Hope this is helpful!

-gus