The difference between the simple double check assembly and the RPZ is that the RPZ has a relief assembly in between the two check valves, that way if either check valve is "Leaking past their seat" the excess pressure this would place on the relief will cause it to vent to atmosphere. The added protection this provides, is that no matter which check valve is not seating, or even if both are not seating the AF cannot go back into the potable supply. In the double check if both checks are not properly seating you can have contamination of the water supply and No indication that either check has failed. (No dripping from the relief as in the RPZ)
BFP's are not intended to control pressure on the discharge side, they are to control the movement of water in a single direction only. The reason many AHJ's like the RPZ only rule is it keeps their life simple, and they show you when they are failing by discharging to the atmosphere. (That is of course unless the relief is also failing.) BFP was the best sales pitch ever! High cost! High maintenance! Limited proven effectiveness in eliminating an unproven problem. -----Original Message----- From: [email protected] [mailto:[email protected]] On Behalf Of Greg McGahan Sent: Friday, April 01, 2011 10:53 AM To: [email protected] Subject: Re: figure 7.6.3.4 - antifreeze loop with relief valve I haven't been to the backflow testing and repair class, but if you are correct, then what good is an RPZ if it does not keep the pressure on the discharge side from being greater than on the supply side? I thought that was the basis of operation for an RPZ? If it is not, please explain. Thanks On Fri, Apr 1, 2011 at 11:29 AM, Thom <[email protected]> wrote: > Greg: > > A RPZ has NO (0) ability to relieve pressure on the discharge side (system > side) after the #2 check valve. The only way for the intermediate relief > chamber to relieve pressure from the other side of the #2 check (The > discharge or system side) is if that check valve is leaking back into the > intermediate chamber. That is not the normal operating situation. With > expansion occurring on the discharge side of the #2 check, (In the AF > system) the backflow should not relieve it, it will simply increase the > system side pressure, further sealing the #2 check against backflow. > _______________________________________________ Sprinklerforum mailing list [email protected] http://fireball.firesprinkler.org/mailman/listinfo/sprinklerforum For Technical Assistance, send an email to: [email protected] To Unsubscribe, send an email to:[email protected] (Put the word unsubscribe in the subject field)
