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Dr.Pressure

New Member

Posts: 3

Location: USA

1

Tuesday, June 26th 2007, 5:46pm

Designing mainline for cold-climate winterization

Hi, sprinkler system design newbie here.

I was ecstatic to find out that the water company in my community will install a second water meter for free to supply my irrigation system. However, my question is how to design for winterization of the mainline from the downstream side of the new water meter up to the side of the house (to be buried below frost line ~36" deep) where my PVB backflow device will be installed above ground. The tutorial at www.irrigationtutorials.com indicates that a manual drain valve is a cross-connection no-no prior to the backflow device so i am curious how to drain the portion of the mainline where it rises out of the ground to the PVB?

Right now my only thought was to install a tee in the mainline down below the frost line which rises to a capped nipple. Then, after the water meter was isolated and the line bled of pressure, the cap could be removed and the vertical portion of the mainline up to the inlet of the PVB could be blown out with compressed air. What isn't clear to me is whether the capped nipple would also constitute a potential cross-connection according to code (I am hoping it would not since it is capped without a valve and it shouldn't qualify as a use point).



I wouldn't be surprised if there is a simpler/better way to deal with this that I am unaware of. Anyone else designed for a similar situation?

HooKooDooKu

Supreme Member

2

Tuesday, June 26th 2007, 6:06pm

From what I've read, what you are discribing would be in violation of code. The primary problem is an air compressor is considered a source of contamination (for example, it should have lubricants that could get pushed out by the compressor into the lines). If the isolation valve were mistakenly not turned off before starting the blow out process, you could essentially be blowing lubricants into the potable water supply.

It seems like the solution I've read elsewhere is to remove the backflow preventer as a part of the winterization process (unions). Then use a wet/dry shop vac to suction the water out of the vertical pipe. (For just that reason, you might want to make the vertical pipe approcing the backflow a little oversized.)

Dr.Pressure

New Member

Posts: 3

Location: USA

3

Tuesday, June 26th 2007, 7:01pm

Thanks HooKooDooKu. It seems that if the isolation valve were not closed, one would get 50-60 PSIG water in their face when the cap was removed[:p]

After surfing a bit more, another option I have come across is to install a stop and waste ball valve after the meter connection in a valve box. This option would also conventiently allow one to run the section of line downstream of the stop and waste valve above the frost line. However, it does appear that some municipalities have disallowed the use of these types of valves underground.

I guess I should talk to a local inspector to get an "official" opinion on what is permissible and common in my area.

Wet_Boots

Supreme Member

Posts: 4,027

Location: Metro NYC

4

Wednesday, June 27th 2007, 4:19am

Where is the second meter going to be located? If in a curbside meter pit, one might have a boiler drain (or a cap or a plug) located there, and use it to blow out the entire system. That includes the PVB. There is no need to install the mainline below the frost line.

The problem with any codes that would declare any 'use point' as forbidden, is that there are testcocks on every PVB or RPZ or DCVA that would fit the concept of 'use point' ~ those testcocks are needed, and they aren't going away.


Dr.Pressure

New Member

Posts: 3

Location: USA

5

Wednesday, June 27th 2007, 7:53am

Thank you for the response Wet Boots. Your explanation about ‘use point’ makes a lot of sense. ‘Use point’ was my term for a possible point where one could hook up a fitting and supply something with water off the pressured mainline. I can see that the testcocks on the backflow devices would be analogous to a capped nipple.

The second meter is going to be in a curbside meter pit. However, I think my problem is solved. In talking with the water company again today, they said when I call them to deactivate the meter in the fall, they actually remove the meter from the pit. This should allow the mainline to free drain if sloped properly and/or be blown out.

Wet_Boots

Supreme Member

Posts: 4,027

Location: Metro NYC

6

Thursday, June 28th 2007, 2:25pm

One thing to ask the water company is whether there will be a downstream shutoff valve on their installation. If not, you want to supply one, so that the drain you have in the meter pit will be usable for blowing out the system after the water company pulls the meter.

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