Master Valve on Discharge Side: Why?

Discussion in 'Irrigation' started by ACC, Oct 1, 2012.

  1. ACC

    ACC LawnSite Member
    Messages: 65

    What are the main reasons for locating the master valve at the discharge of an RPZ backflow preventer instead of the inlet?

    My best guess is that the water pressure to the RPZ will be more consistent and so the RPZ's valves' seats won't experience as much wear and tear.

    I cannot think of how there is a greater risk of cross connection contamination with the master valve at the inlet to the RPZ, but maybe I am missing something.

    My HOA's board is asking. A few of its 70+ RPZs have the master valve at the inlet to the RPZ. The city has suggested, but not mandated, ensuring all the master valves are at the discharge of the RPZs. The HOA's irrigation system is some 25-years-old and has been modified many times over the years. It originally had AVBs.

    Thanks in advance for your pro bono help to my blue collar neighborhood.
  2. Wet_Boots

    Wet_Boots LawnSite Fanatic
    Messages: 50,751

    Only the atmospheric vacuum breakers are intended for intermittent pressure. All of the assemblies with testcocks are to be pressurized 24/7, until they are drained for winter.
  3. cjohn2000

    cjohn2000 LawnSite Senior Member
    Messages: 570

    Thats odd, never heard of a master valve on the inlet side of an RPZ. The only contamination possibility is if you used the bleed screw and somehow contaminated water go sucked back in to the valve.
  4. Mdirrigation

    Mdirrigation LawnSite Gold Member
    Messages: 3,793

    The master valve is part of the sprinkler system , The backflow preventer is part of the house plumbing . Anything on the supply side of the backflow is plumbers territory , anything past the backflow is sprinkler guy territory . having a MV before the backflow , it would have to be installed by the plumber , and serviced by the plumber.
  5. AI Inc

    AI Inc LawnSite Fanatic
    Messages: 27,061

    Thats the way I see it.
  6. ACC

    ACC LawnSite Member
    Messages: 65

    Thank you Wet Boots, cjohn, mdirr and Al. Your comments help. Texas's code says that the purpose is to ensure 'accurate testing of the backflow preventer.' A lab engineer/tech at fccchr said on the phone that a non-constant pressure and so all the resultant cycling of the backflow parts tend to promote a higher fail rate, hence the recommendation in general and requirement for new installations in many states.

    Whether it is worth the thousand dollars or so to move the master valve to the discharge side on old installations seems a guess to me. Liability issues are big here at the HOA, so with a stretch of reasoning, this might justify the expense.
  7. Wet_Boots

    Wet_Boots LawnSite Fanatic
    Messages: 50,751

    As long as you have no issues with higher fail rates, you can keep things as is. Performance is certainly not going to be better than customary, and it could be quite worse. I remember PVBs failing at less than two years of age, when a normal installation would have given over a decade of worry-free service.
  8. irritation

    irritation LawnSite Gold Member
    Messages: 3,594

    USC Foundation for Cross-Connection Control and Hydraulic Research states there should be no valves or tees between main shut off valve and backflow preventer.
  9. Wet_Boots

    Wet_Boots LawnSite Fanatic
    Messages: 50,751

    I kind of doubt that Albuquerque cares about USC. I don't have to. It's more a cost-of-maintenance issue. It won't take many RPZ repair kits to make not moving the valves seem really stupid.
  10. irritation

    irritation LawnSite Gold Member
    Messages: 3,594

    I think most water purveyors use the USC guidelines.
    I remember when the clean water act and IDEM got involved. We just finished a new install at a restaurant and had a quick coupler before the PVB, they made us cut it out. Had to use a Leary bicycle pump to clear the water before the backflows. I have no comment on later years. :rolleyes:

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