backflow preventer's vent leaking

zepfan

just finished re piping a hot water boiler system, and and made the existing one zone house, into a four zone house with four separate thermostats, and zone valves. Eliminated the existing steel expansion tank, and added a diaphragm type expansion tank, and air eliminator at the outlet of the boiler. All turned out well, with the exception of the existing backflow preventer's vent is now dripping water at all times. Does not matter if the cirulator is on, or off. The bf preventer is in the same line as the prv, and enters the system about three feet before the inlet of the circulator. my question is does it matter where these are piped now that the tank is pressurized rather then a conventional steel expansion tank? I don't think it does, and that the bf preventer just has to be replaced. Any assistance would be much appreciated, thanks to all

Mark Eatherton

It' doesn't matter where it's placed in the system. It has crap under its seat, and if it can't be disassembled and cleaned, it needs replaced. If there is an appliance in the home that can create a major pressure drop (Flush-o-meter toilet valve for example) it is common for this device to "spit" on occasions when the Flush-o-meter is used. If that's the case, it is acceptable to install a single seated spring check valve before the BFP so that it doesn't "see" the pressure droop when the Flush-o-meter is used.

ME

hot_rod

This type of dual check? There is a spool inside that closes off the vent port when pressure is first applied, noted by the grey line with circle.

Usually something gets stuck between that o-ring, the t shape black and the end of the brass spool. Teflon tape shards, solder balls, copper shavings, rust, dirt, etc. It only takes a speck of debris to cause a drip.

The second nut from the left hand end allows you to open up the valve, remove the spool and clean off the surface. Sometimes you can reach in through the vent port and clean out the debris.

Unless the o-ring has been nicked or damaged you can usually fix a dripping BFD.

An intermittent drip is sometimes caused by pressure surge and droop, like a solenoid valve or flushometer hammering off. An additional swing check upstream, or a water hammer arrester can sometimes solve problematic/ occasional BFD drips.

newagedawn

time for a new one, went that far now go the extra mile

zepfan

Thanks for the responses, the bf is a the standard 1/2" watts 9d. I will try to attach a photo of the install

the_donut

Some of the cast iron bf body wear around the seat making a repair kit worthless. Less time to swap than rebuild.

realtorin

Hello all. I understand having a drip from the vent line and gunk between the seat and disk. The issue I'm having is when in either potable water or salt water mode I have a solid stream of leakage. Anyone have this issue to date? A new one is only $68 from Grainger.
Thank you.

Gilmorrie

There is, or a least used to be, a rebuild kit for the Watts 9D. However, I recall somebody in the past reported that the cost of a new unit isn't that much more than the rebuild kit. I would go with a new one.