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Water Hammer 101

irrig8r

LawnSite Platinum Member
Seems I need a refresher course on this subject.

Looked at a job yesterday where they want add to a couple of drip systems and split an existing one, and need help with lawn head spacing.

Former owner was a DIY, combined with lawn changes when a brick patio was added and sprinklers moved...

Heads too close in some spots and too far in others, and mismatched nozzles all the way around...

In ground in-line valves were replaced by some one with Rain Jet RJ711s anti-siphon valves along the way. The system comes off 3/4 copper pipe at the rear of the house and measures 50 PSI static at the hose bib at the same tee as the POC...

A couple of the lines have water hammer problems when the valves shut off. The worst has what looks like three 15F and one 15H spray heads on it.

Should draw something like 10.5 GPM, right?

10 GPM through CL 200 comes to 4.72 FPS according to the chart, just above the 5 FPS "red zone"...

So in order to make all that water hammer racket (about 20 "kicks" after the valve closes) there must be more water going through the line than I thought...

Cranking the manual flow control knob down I was able to reduce the number of "kicks" some... but doesn't that also make the valve close faster? And isn't a fast closing valve part of the problem?

I have never added a water hammer arrester... my recollection is that they just sort of fill up with water over time and have to be emptied...

And I don't think I've ever seen water hammer at this pressure range before, usually much higher.

I watched this manifold pulsing... scary stuff... so I'd like to fix the problem and not create any more...
 

Mike Leary

LawnSite Fanatic
Rain-Jet?..Jeez, we'd forgotten what a quality product that is!
Are you that low on work, Greg? I think you are exceeding the 5' rule.
Deep pockets? we've talked about this before...spare wire? Split zones?
Start over? MP Rotators?
 

Wet_Boots

LawnSite Fanatic
Location
metro NYC
Would they even bother manufacturing a crummy diaphragm? Seems like too much effort. I think they do use a bonnet that doesn't have the manual-open lever on it, so it can be declared to be a lesser item than a 2711APR
 

PurpHaze

LawnSite Fanatic
Location
Visalia, CA
A couple of the lines have water hammer problems when the valves shut off. The worst has what looks like three 15F and one 15H spray heads on it.

Should draw something like 10.5 GPM, right?

10 GPM through CL 200 comes to 4.72 FPS according to the chart, just above the 5 FPS "red zone"...
General rule of thumb on 15' sprays is 1 GPM for Qs, 2GPM for Hs, 3 GPM for 3/4s and 4 GPM for Fs which would total 14 GPM in your case. Without the brand/model of nozzle and without looking at their charts it's only guesswork.
 

PurpHaze

LawnSite Fanatic
Location
Visalia, CA
Cranking the manual flow control knob down I was able to reduce the number of "kicks" some... but doesn't that also make the valve close faster? And isn't a fast closing valve part of the problem?
Total amount of closure time is reduced when you throttle down the flow control but what you've done is reduce the flow through the valve in the first place. This allows the diaphragm to overcome the water flow and pressure sooner.

All automatic valves are slow closing for their first 85% of closure and then are considered fast in the last 15% when the diaphragm finally seats.
 
OP
irrig8r

irrig8r

LawnSite Platinum Member
Would they even bother manufacturing a crummy diaphragm? Seems like too much effort. I think they do use a bonnet that doesn't have the manual-open lever on it, so it can be declared to be a lesser item than a 2711APR
The only apparent difference is the lack of a lever under the solenoid, and the color.

My recollection is that Rain Jet and Safe-T-Lawn were merged with Hydro Rain to become Hardie. Then Richdel, Irritrol and Hardie got together under the Irritrol banner, and finally Irritrol was bought by Toro.

Rain Jet and Lawn Genie are DIY versions of Richdel valves. The diaphragms all appear to be interchangeable. Lawn Genie was owned by Black and Decker for a while, but no longer as far as I remember.
 
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