SPRINKLER TALK FORUM - You Got Questions, We've Got Answers

I copied this from Jess strykers tutorial and it was the source of the 7 ft per second rule that I stated.


Water Hammer

True water hammer is essentially the sound of a "water wreck" occurring. It happens when moving water suddenly changes speed. Water hammer can be caused by a pump starting or a valve rapidly opening, however in the vast majority of cases it results when a valve closes. Sometimes you can create it simply by closing a faucet very fast. Many single lever household sink faucets will allow you to slam them closed fast enough to cause water hammer. Closing the same valve slowly will not cause the water hammer. However, more often the valve causing the problem is an automatic valve such as is used on an irrigation system. Since most dishwashers and washing machines use the same type of valves as irrigation systems, you will sometimes get water hammer when the dishwasher or washing machine fill valve closes. So for this tutorial I am going to focus on water hammer caused by closing valves. Even though these so-called "electric valves" appear to be powered by electricity, they actually use water pressure as their major power source. The electric solenoid on the valve operates a tiny "pilot valve". The water flow from this tiny valve is then used to open and close the bigger valve using hydraulic pressure. This works well, but leaves a minor engineering problem. It is very hard to get these valves to close slowly! Engineers have made some great progress but they still haven't fully defeated what I call the 80/20 problem. The 80/20 problem is that valves close slowly until they are about 80% closed, then they tend to snap fully closed in a millisecond! This causes the water in the pipes to suddenly stop moving. Now we all know the story of Jack and Jill, and the reason Jack fell down is that water is heavy (and perhaps Jack was paying too much attention to Jill , and not enough to his bucket, but I'm getting off-track here.) A column of water moving through the pipe at 7 feet per second carries with it a tremendous amount of weight and momentum. While it's not a perfect example, the one commonly used is to think of the water in the pipe as a big freight train going through a long tunnel. The valve closing is like blocking the end of the tunnel with thousands of tons of rock. When the train slams into the blocked end of the tunnel there is going to be one horrific crash! The faster that train is moving, the worse the crash will be. Thus the problem with water velocity in the pipe. The faster the water is moving, the worse the crash is going to be when the valve closes. That crash is the cause of a big thumping noise when the valve closes. Secondary thumps that follow are essentially "echoes" in the pipe.

Listen. With 1 inch pipe you dont want over 18 gpm. I think this is according to Jess tutorial. It has to do with velocity of the water going thru the pipes. If memory serves me correctly its like 7 ft per second. Ill see if I can find my source.

If you don't need more distance from the sprinklers, then you don't need more pressure at the sprinklers. If the original install is unsatisfactory to you, you may never be satisfied until it's completely done over again. In that case, you would start with a new pump in the well, and new numbers for flow and pressure, and a new layout with new heads and pipe. If the existing system can keep the lawn green, regardless of watering time, there isn't a tremendous need to change anything. If it doesn't satisfy you, why take any half-measures short of an entire new system? Anything inbetween is to be dealt with by someone who will charge you by the hour to visit the property and evaluate the system.

no not really ..i laid the sprinklers out the first set was laid out on the 1/2acre the house is on well i messed up when i designed it b/c i listen to a guy at home depot big mistake ii ran the system with 1" pvc b/c thats what he told me to do..well he had me run one zone for the back yard and frt yard he tl=old me i could run like 18 k-rain k2 rotors on one zone so i did big mistake well i had to go back and add another zone one for the frt yard and one for the back ..well when i bought the 1/2 acres next door i installed sprinklers on that also well i learned something from the first time.i only installed 6 heads per zone but now theres a alot of pvc in the ground to go from the house where the valves are to across the yard and split out one zone has maybe 250ft of pvc from the valve to the last head i know now i should have went with bigger pipe like maybe 1-1/2 to 2" into the yard and then branched off..i am just trying to find a fix with out digging the whole yard up and starting over ....most of if not all of the rotors have head to head coverage ....i have been talking to a well guy that i am friends with and he seems to think i could get done what i want if i go with a bigger pump ...i called sta-rite pump company talked to 2 different guys and got 2 different answers so whos right ? tks for all the help wet boots i know you don't have to help but i am glad you offer your help......

Do you need more distance from the rotors?

besides going to smaller nozzles how could i increase the psi at the rotor.would a bigger pump do this

In theory, that could mean that the well was pumped at a rate of 40 gpm, and didn't run out of water. I say theory, because I've worked with 'official-looking' performance figures provided by a well driller, that weren't even close to the (much less) true performance of the well. The government records of well performance serve a purpose of keeping an eye on all possible sources of potable water. You might think it's your water, but it actually belongs to the state, as long-ago established as being for the common good.

i found my well info off the internet from the county records....its a 4" casing casing depth 68' total depth 82' need some help with this one AIR (YIELD GPM) is 40 what does this mean my max out of the well is 40gpm?

well i dug up my old sprinkler design info and when i did the old 5 gallon bucket test i came up with 18gpm so i could go with a 25gpm pump and that would almost be a 50% increase if i did that would that also increase my sprinkler line pressure or only the flow?

i will do some checking..........i was looking at my k-rain nozzle chart and they seem to (according to the chart)throw water futher then the hunter i-20 what gives with that how can k-rain nozzle throw water futher at the same psi then a hunter I-20 ?