Golf Committee’s Irrigation Subcommittee Report

 February 3, 2009 Meeting

Bob Pleski

 

Attendees:  Ken Wolford, Ed Lauchner, Tom Watson, Bob Pleski

 

Item A: We reviewed the pipe-break data that was provided by Ken Wolford a couple of months ago that covered breakage up through September 4, 2008.  There were 17 breaks; one break on the mainline, and the rest were all in the laterals or a broken sprinkler head.  Of the 16 breaks on the laterals and head, six were on the front nine and 10 were on the back nine. 

 

Item B: We discussed the Toro video that we watched about the reduction in water hammer with heads that are slow turn-on/off, and the consensus was slow turn-on/off put less stress on the pipes than fast turn-on/off. 

 

Item C: I have been in contact with the superintendent at The Ridge Golf Course in Auburn.  They have a Flowtronics Pump Station similar to ours and the pressure leaving their station is 115 psi for the lower elevation and 140 psi for the higher elevations.  They use slow turn-on/off heads, mostly Toro, but does include some Hunter.  They have had no pipe breaks in the past two years. 

 

              We did some analysis of the flow in the pipes and using Newton's second law of physics, which covers the basics of acceleration (also deceleration) which uses the main formula:

 

                                    F= Ma   (Force = Mass x acceleration)

                                    (acceleration = ft/sec. squared

                                    F=M x ft/sec. squared

 

Looking at a typical 1/1/2" pipe, 60 ft long and ending at one head, putting out 27 gpm, there is approximately 58 lbs of water in the pipe flowing at 4.2 ft per second and this flow is stopped when the sprinkler shuts off.  We don't know what the shut-off time is on the Rainbird heads, but we do know it is fast.  If it shuts off in 100 milliseconds (1/10th of a sec.) then the force will be 100 times the force as if it shut off in one second.  This force tends to pull the pipe in the direction the water was going and puts stress on the elbow near the water main, and this most likely causes the elbow or tee to crack on the inside bend. 

 

Again,  we agreed that slow turn-on/off heads put less stress on our pipes. 

 

The sudden stopping of water also puts a high-peak pressure on the pipe and all fittings, and this transmits through the water at the speed of sound in water, approximately 4800 ft/second.  This is why we see so much needle movement when we try to measure our pressure with the strip-chart recorder that we have been using.

 

Item D:  Are we in agreement that when the sprinkler heads are replaced we will use only heads that provide a slow turn-on/off?  There was not an unanimous agreement on this question.

 

Item E:  When we did a catch-can test on the 15th fairway on Sept. 5, 2008, we found that the distribution uniformity was very good on the Rainbird heads, calculated to be 88%.  However, some of the areas where observation was made that the grass appeared dry, had 100-115 grams collected versus the average of 137 grams. 

 

Question:  Why does there appear to be so noticeable a difference in grass color and soil firmness for such a small difference in water collected? 

 

Answer:  The consensus was that the soil is hydrophobic (not capable of uniting with or absorbing water). 

 

Question:  What can be done to treat this hydrophobic soil?

 

Answer:  Wetting agents are available that should eliminate this condition over time. 

 

Item F:  We have about 20 donated Toro sprinkler heads and we would like to have 10 installed in the exact location where we tested the 10 sprinklers on the 15th fairway.  Because there are different part numbers of Toro heads donated, Kevin Eppich (Toro) should be contacted and he should tell us which ones he thinks we should put on the 15th fairway and which ones on the 17th.  He should also specify what pressure settings they should be set at before being installed. 

 

Ken plans to have the ones on the 15th fairway installed by the end of March 2009. 

 

We have 10 or more that we want to have installed on the 17th fairway.  Before we install these, we want to do another catch-can test of the Rainbird heads and then do another catch-can test with the Toro heads.  These will be left in and observed at the end of the dry season of summer and fall. 

 

Item G:  Toro is doing a calculation of distribution uniformity of our 9/05/08 water collection and they have not yet responded.  Ken is to contact Toro to get the results.

 

Item H:  We want to get acquainted with the Dickson pressure data logger that was loaned to LWW by Kevin Eppich and then use it to monitor pressure during a regular watering cycle this summer.  We should contact Kevin and see if we can keep it that long, or return it and borrow it again.  This pressure data logger takes a reading of pressure every 10 seconds and can collect up to 32,000 samples before it records over the prior data, about 90 hours.  According to my contact with Dickson, this model is unlikely to record the peak water pressure caused by water hammer.  If we want to capture this peak pressure, we would need another model that records data every second and will record for about nine hours.