# RPZ Minimizing Pressure Loss

Discussion in 'Irrigation' started by dypsisdean, Sep 4, 2010.

1. ### 1idejimLawnSite FanaticMale, from State of JeffersonPosts: 9,437

i've built pools for a long time, my dad since the 50's.

i've plumbed both commercial and residential, spas, caretaker systems, negative edge ect. i also do leak detection.

in a way you're right about drawing board vs field work but, without the drawing board specs, i find it hard to make field decisions without some doubt, and i don't like doubt.

i've seen other contractors move an equipment pad 40 feet not taking into account for an additional 10' of rise. performance will suffer if you do not do your math.

taking measurements is not that hard, if you can't physically see the meter you can bet that the water purveyor can give you gpm statistics.

a working pressure test can be taken at each head with a pitot tube and a liquid filled gauge, or by unscrewing the head and putting a test tee under the rotar head. hunter makes a rotor pitot for about \$50

removing a head and using a flow meter will give you an idea of you supply at any given point.

you have a pressure gain of approx.40 psi with your elevation gain, now the loss due to friction can be calc'd over the +/-500'.

lets see, you could install a schrader valve at each valve and get a pressure right there.

btw, how do you shut off the water for maintenance? did you think to install a master valve and flow switch, might help in case of a catastrophic failure

2. ### dypsisdeanLawnSite Memberfrom HawaiiPosts: 38

I doubt you would come out on the winning end if comparing degrees. Although I will admit, I did have some difficulty with 2nd year calculus while pursuing my B.S. in Physics.

But why anyone would think they could determine my mathematical abilities based on the above conversation, is beyond me - and my last word.

3. ### KirilLawnSite Fanaticfrom District 9 CAPosts: 18,308

If you believe this, then you clearly don't know much of anything about sprinkler system design. No offense dude, but why did you come in here asking questions if you already have all the answers? Furthermore, why the hell are you using compression fittings?

While this is true to an extent, the reason an accurate board design isn't completely represented in the field is because the installation violates the parameters of the board design.

4. ### KirilLawnSite Fanaticfrom District 9 CAPosts: 18,308

I wouldn't bet on it bud .... given one of my degrees is in soil science and hydrology.

Because you continue to argue you don't need to know flow when that IS what you need to know in order to determine the performance of an RPZ.

5. ### Mike LearyLawnSite Fanaticfrom Cactus Hug, ArizonaPosts: 21,976

I think you can get one of these at one of the box stores, should solve all your problems.

6. ### dypsisdeanLawnSite Memberfrom HawaiiPosts: 38

I lied. I would like to reply since you took the time for a thoughtful response. Everything you say is true. However, I think my original question got lost. All those facts and figures are not needed to answer my original question. I already have a system that is working really well. Whatever the exact flows, pressures, etc. are doesn't really matter at this point. All I wanted to know was if there was anyway to preserve or provide for the same flows, pressures, etc. after the installation of an RPZ? Or if there were some RPZs that did a better job in that department than others? Or if oversizing might help?

If the answer is "no" to all of those questions, then that is all I need. I can figure out the rest. It is the RPZ that I have no experience with.

And no, the previous owner/builder did not think to provide for emergency shut off given the distance to the meter. I have shut off to the house, and I installed convenient shut off for the irrigation lines and system. But for everything else I jump in the utility vehicle for a quick jaunt up the hill and shut things off at the meter.

7. ### dypsisdeanLawnSite Memberfrom HawaiiPosts: 38

Thanks Mike,

Let's just see what happens if I supply the flow for those claiming they can't help me without it.

OK, my flow is 40-45 gpm. I had to determine flows for 30 years, with and without flow meters. All commercial pools had flowmeters. I could look at the flow into a pool from any type pump and tell you within 5 gpm what the flow was. I would bet big money my flow at my main downhill 1" full port valve wide open is 40-45 gpm. So, now you "experts" have the flow. How will that help you answer my original question any better?

8. ### KirilLawnSite Fanaticfrom District 9 CAPosts: 18,308

WOW ... you and boots should get together because he has a three variable equation that can do the same thing.

Certainly at some point in your schooling you learned how to read a graph?

As I said before, look it up.

9. ### dypsisdeanLawnSite Memberfrom HawaiiPosts: 38

So let's make this simple.

Based on my experience and "feel" I would say that by upgrading to a 1 inch meter and matching the RPZ to the 1 1/4 inch downhill supply line that I would preserve or exceed the present capacity of the existing 3/4 inch meter and no backflow device. This was the main thrust of my original question.

Any "professionals" out there willing to hazard a guess without a page full of math and graphs?

Last edited: Sep 5, 2010
10. ### 1idejimLawnSite FanaticMale, from State of JeffersonPosts: 9,437

that's what i can't figure, if you can access the meter you can at least time the the meter and get a flow rate, if you can't see the meter face then the purveyor is reading it with a tube or electronically, in that case you have the controller set, ask for a reading, spend the night with friends and get the other reading before you use any water, this can be prearranged.

everything else has been layed out for you, without the current statistics, how will you know if the rpz will hurt the system or not?