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The last 10 posts

Wednesday, October 18th 2006, 4:18pm

by HooKooDooKu

But as a basic follow-up, if you have lots of static pressure to begin with (like 100psi or more), then the loss in the RPZ won't matter much, except that you would need to adjust the pressure from any pressure regulator you should have if your static pressure was over about 80psi to begin with.

But if your system was designed with just enough pressure, the RPZ could be enough for the system to not provide enough pressure at the heads. If that happes, you might need to look into replacing your spray heads with MP-Rotators. They use low gpm compared to regular heads. This would greatly reduce your friction losses. When you drop the flow by half, the pressure losses reduce by MORE than half.

Wednesday, October 18th 2006, 4:11pm

by HooKooDooKu

Depends upon how much pressure you have to start.

As a general guess, your heads need about 20psi to operate. What you have to do is start with the static pressure of your system and subtract all your pressure losses. If you still have about 15-30psi left, your system should be ok.

While you really need to take the time to review everything at www.irrigationtutorials.com, here's the basics.

Get a pressure guage and use a hose bibb source by your water line before any pressure regulator and read your static pressure. Start with that and here goes some estimates.
Drop 3 psi for the watermeter.
Drop 5 psi for the irrigation valves.
Drop 12-15 psi for the RPZ.

The last part is friction losses throught the pipe. Assuming everything is 3/4" Sch40 PVC, flows of 5gal/min = 5.7 psi loss per each 100 foot. 7gpm = 10.5psi/100' and 10gal/min = 20psi/100'.

So you've got to know how much water is flowing through each pipe, it's length, and do the math (so you need the gpm figures for the spray heads).

The last thing to consider is that water losses 4psi for every 10ft of elevation change.

Wednesday, October 18th 2006, 12:23pm

by JohnnyG101

The zones have no more then 4 heads and most have 3. Will the pressure loss be that noticable?

Wednesday, October 18th 2006, 10:44am

by HooKooDooKu

It depends upon which model and size you buy AND what the flow rate is.

You can look at http://www.watts.com/pdf/ES-009.pdf to find the pressure loss charts.

If you installed a Watts 3/4" RPZ Model 009, you will have about 14psi loss for flows between 1-12 gpm. But if you install the 1" version, you'll only get a 10psi loss at 20gpm (but it's 14psi for 5-10gpm).

I believe Febco is one of the other popular makers of RPZ for irrigation, but I don't have a link to thier specks.

Tuesday, October 17th 2006, 2:51pm

by JohnnyG101

I spoke to the city again, and the RPZ is REQUIRED. And has to be installed by a licensed professional. So I guess am I out of luck doing this myself.

I am hearing conflicting accounts on the pressure loss after this is installed. Some say 10-15 and other say no more then 7. Well which is it? The idiot only used 3/4" PVC as well. Im so screwed.

Sunday, October 15th 2006, 11:33am

by Wet_Boots

Shut the entire house off, and run the air through an existing hose bib.

Sunday, October 15th 2006, 8:11am

by JohnnyG101

Thanks for the info. I am probably going to install this in the spring.

The previous owner never installed any drains so without the backflow or drains, I have no clue how I am going to winterize this thing. I was told the 3 years the other guy lived here, he never winterized....

Wednesday, October 11th 2006, 6:16am

by HooKooDooKu

<blockquote id="quote"><font size="1" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote"><i>Originally posted by JohnnyG101</i>
<br />I was told that all I needed was an RPZ. Can anyone make a reccomendation on which to get?
<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">

An RPZ is what is considered the "strongest" of backflow options (i.e. most reliable at preventing backflow, almost no codes would ever prohibit its use). But as Wet_Boots points out, installing an RPZ could affect your systems performance because it's going to rob the system of 10-15psi operation pressure.

You might want to check with codes again and see if a lower-end backflow option is available. Again, as Wet_Boots points out, a PVB will steel less operating pressure from the system. I believe MOST building codes allow PVBs, but it has to be installed above the highest sprinkler head (RPZ only has to be installed above ground, relative position to rest of irrigation system doesn't mater).

The third option (and more likely to be disallowed by local codes than the PVB) is a DC (double check). Don't confuse this with a double check valve. A DC backflow preventer has test cocks with it so that after it has been installed, each check valve can be independently tested for proper operation. There is no way to verify that each check valve is working properly in a double check valve. A DC is considered the least safe option (and not recommended if anything is injected into the system such as a fertigation system). However it has the benefit that it can be installed just about anywhere. This would include a basement or underground in a meter box. An RPZ can't be installed in a basement (unless you have adequate drainage for the water that can spew from the device) and you can't install it underground (it can't be located such that the device becomes submerged should it start releasing water to prevent backflow).


<blockquote id="quote"><font size="1" face="Verdana, Arial, Helvetica" id="quote">quote:<hr height="1" noshade id="quote"><i>Originally posted by JohnnyG101</i>
<br />The height is no issue at all. Also, it doesnt look like the dude installed a drain valve either.

This is needed no? How else could I drain the main line before it hits any valves right?
<hr height="1" noshade id="quote"></blockquote id="quote"></font id="quote">
While installing the backflow, you can install a blowout port (AFTER the backflow preventer). The blowout port would allow you to connect an air compressor to the system and blow all the water out of the irrigation system (winterizing).

Tuesday, October 10th 2006, 12:56pm

by JohnnyG101

The height is no issue at all. Also, it doesnt look like the dude installed a drain valve either.

This is needed no? How else could I drain the main line before it hits any valves right?

Tuesday, October 10th 2006, 12:45pm

by Wet_Boots

An RPZ will subtract 10-15 psi from your operating pressure. That's enough to affect performance. If elevation allows installation higher than any sprinkler head, then a Pressure Vacuum Breaker is a better choice. Cheaper, too.