Sprinklers and Home Water Physics

[Carborendum]

11 hours ago, zil2 said:

 a new sprinkler controller that has a "water hammer" feature that will open the next valve 10 seconds before the current valve shuts off.  As long as my first and last zones are the ones least likely to trigger water hammer

... do you think this will help?  It sure seems like it would - two valves running at once would lower the pressure on both of them, no?

Yes, it will help.  Here is the mechanism:

Consider when you pour a drink from a 2L bottle. 

• As long as you pour slowly enough, the soda will not plug up the opening.  The soda flows freely as air flows into the top part of the opening.  This tends to fail at about an 80% to 90% depth (i.e. the opening is about 1", so at 0.8" soda depth to 0.9"soda depth).  Above that, minor fluxutations in the flow depth as well as the air intake requirement to displace the liquid going out causes too much turbulence to be dependable.
• At that failure point, it will try to compress the bottle.  But then it will start hiccuping by sucking air back and forth.  This is an alternative to water hammer if the "pipe" is effectively compressible.  Plumbing pipes are effectively incompressible.  So, instead of the hiccuping, we experience water hammer.
• If you put a hole in the opposite end of the bottle, air can be sucked into the bottle on one end while the fluid flows through the other end.

Water hammer occurs when the system has no expansion/compression ability.  Water is incompressible. Plumbing pipes are effectively incompressible.  Perhaps if liquid in question has a lower heat of vaporization, it may just evaporate.  But water has a high heat of vaporization, so...

When you turn on or off the only opening (the fixture or sprinkler system) in a brief period of time (i.e.  ΔP/Δt -> ΔP/dt) the system cannot adjust to the rapid change in pressure.  The change in energy has to be attenuated somehow.  So, it moves the pipes and the energy is dissapated via the water hammer.

When ANY fixture is opened, air is introduced.  Air is a compressible fluid.  And that goes in both +/- directions.

Yes, if the first zone is opened or the last zone is closed, you'll hear the hammer as long as the opening/closing mechanisms are both fairly quick.  If there is an overlap between zones, two openings allow for the equalization of pressure becaue air is present in the system on both ends. (an air hole in one end, a water hole in the other).

If you only hear it when the sprinklers turn on, that means the "on" valve is faster than the "close" valve.

[zil2]

59 minutes ago, Carborendum said:

If you put a hole in the opposite end of the bottle, air can be sucked into the bottle on one end while the fluid flows through the other end.

Like a gas can.

1 hour ago, Carborendum said:

Yes, it will help.

  Thank you, especially for the explanation!

So, I talked to the plumbing company today - mostly, I just wanted them to know about the error so they can improve. (I like this plumber - he's not arrogant or unfriendly, and explains what he's doing and why.)  But after the office-person talked to the plumber, they decided to refund my money!  That's a class act, IMO.  I didn't ask them for a refund.  So, I'm going to use half that refund to buy this controller - it's the only residential one I can find that has this feature.  I'd prefer an "old fashioned" one like I have, but it's the only option, so Wi-Fi and "smart" it is - thankfully, I don't have to have any other "smart" stuff, and there's no monthly/annual/service fees.  And technically, once programmed, I could disable its Wi-Fi access and it will work - or I can let it talk to the interwebs and it will adjust watering based on the weather...

I've also found everything I'd need to get to try out a water hammer arrestor.  But I'm thinking the controller is probably the better option, if it will work alone, which it seems like it will. (The water hammer arrestor only lasts a couple/few years, from what I read online - or 10,000 shock cycles, per the manufacturer.)

Anywho, once again, I appreciate all the help and "listening" while I work through this.

[zil2]

1 hour ago, Carborendum said:

Water hammer occurs when the system has no expansion/compression ability.  Water is incompressible. Plumbing pipes are effectively incompressible.

BTW: My morning dive into water hammer arrestors demonstrated this.  I love it when there's a cut-away and/or exploded diagram, and a good explanation of how things work.

[zil2]

13 minutes ago, zil2 said:

So, I'm going to use half that refund to buy this controller - it's the only residential one I can find that has this feature.  I'd prefer an "old fashioned" one like I have, but it's the only option, so Wi-Fi and "smart" it is - thankfully, I don't have to have any other "smart" stuff, and there's no monthly/annual/service fees.  And technically, once programmed, I could disable its Wi-Fi access and it will work - or I can let it talk to the interwebs and it will adjust watering based on the weather...

Oh, and cool deal - I can get a $100 rebate from the state once I've got this thing installed.