back flow preventer

cutter

In my current hot water heating system I have a Watts back flow preventer. When supply water to the entire house is turned off and supply pressure in the house drops to zero the Watts back flow preventer starts dripping out of the vent. I have a new Watts back flow preventer I can install but am having second thoughts. I am considering a Caleffi auto fill and back flow preventer all in one.
What are you guys opinions on a trouble free back flow preventer?

Docfletcher

The back flow preventer needs pressure from both the house (Street pressure) side and the boiler side in order for it not to drip.

ChrisJ

Docfletcher said:

The back flow preventer needs pressure from both the house (Street pressure) side and the boiler side in order for it not to drip.

My BFP very often has no pressure on the boiler side, and sometimes none on the street side and it doesn't drip?

I thought the only time the "vent" actually vented was if the boiler side's pressure is higher than the street side?

To me, it sounds like the OP's BFP is working as designed.

hot_rod

Here is a cutaway view, of a Caleffi, and it's typical of other brands of this style.

There are 3 seals that need to be tight.

There is a spool inside that pushes close to seal off the vent port. There is a check on the upside, and one down side of the spool.

If any of those have even a spec of dirt or debris you can have a drip or leak.

The only way for boiler side to leak back is the second check would be leaking and the spool open or leaking also.

Usually a disassembly and cleaning solves the drip, but replacement is often the easier fix.

Regardless of the brand they are a finicky valve.

A screen upstream, included in most, can help keep crud out.

cutter

ChrisJ said:

Docfletcher said:

The back flow preventer needs pressure from both the house (Street pressure) side and the boiler side in order for it not to drip.

My BFP very often has no pressure on the boiler side, and sometimes none on the street side and it doesn't drip?

I thought the only time the "vent" actually vented was if the boiler side's pressure is higher than the street side?

To me, it sounds like the OP's BFP is working as designed.

I was told that I should turn off the water coming into the house if I should leave for the weekend or longer in case some thing lets loose and i should have a flood. My uncle told me of a neighbor of his that had water running out of his garage for two weeks while he was gone.
So I have turned the water off and when it was turned back on the back flow preventer dripped rather nicely and never did stop. I took it apart and cleaned it up and it stopped once, next time it never did stop. That has been my experience with my watts back flow preventer.
I too have a valve on the boiler side of the back flow preventer and the back flow preventer does not leak when that valve is turned off. Only leaks when the supply side has no pressure.

cutter

hot rod said:

Here is a cutaway view, of a Caleffi, and it's typical of other brands of this style.

There are 3 seals that need to be tight.

There is a spool inside that pushes close to seal off the vent port. There is a check on the upside, and one down side of the spool.

If any of those have even a spec of dirt or debris you can have a drip or leak.

The only way for boiler side to leak back is the second check would be leaking and the spool open or leaking also.

Usually a disassembly and cleaning solves the drip, but replacement is often the easier fix.

Regardless of the brand they are a finicky valve.

A screen upstream, included in most, can help keep crud out.

You are most likely showing a Cafeffi Back floe Preventer but the Watts is very similar. That screen is not very fine. I have had my Watts valve apart a couple of times, once I got it to stop dripping, the next time it would not cooperate. I had well water then, I have city water now so maybe there might be a change. ???????
If they all work that way maybe I will flip a coin to see which one I use

hot_rod

yes that is a Caleffi version cut a way The Watts has a flat washer where the Caleffi has an o-ring at the spool seal.

The challenge with the screen it too fine and they plug instantly, too coarse and they do n to stop debris. It is also a small diameter screen, about the size of a dime.

Pressure spikes in your water pressure may cause them to spit, like fast closing solenoid valves. Sometimes having a water hammer arrester helps if you have high water pressure.

Wash machine valves can be enough to cause them to spit sometimes, with high pressure buildings..

Docfletcher

Well, I've only had the pleasure of using Cashe Acme brand and found that if the BFP does not have constant pressure exerted from the street side it will drip. I've tried 3, two at my home and one at my Sisters and the outcome was the same. They dripped when street pressure was removed.

I just got off the phone with Cash Acme and the lead technical assistance fellow there said that the BFP will leak without the constant pressure applied. He also said the drip should eventually stop, but he could not say exactly when. When I told him the leak does not stop he said there must be a speck of debris preventing it from sealing. So then I told him of two new BFP's vent leaking and he had no answer for that.

Here is the leak to a previous discussion here on the board which sheds more light on the subject.

http://forum.heatinghelp.com/discussion/151986/cash-acme-bfp-backflow-preventer-questions#latest

cutter

Hot Rod, Thanks for your input, seems like I will have problems with any valve if I turn off the supply water. I now have gate valves on each side of the Back Flow preventer. When I re-do the piping I will change to ball valves and close the ball valves if I shut off the supply water. And as was suggested in another discussion run the vent pipe to the floor.

cutter

Docfletcher, Thanks for posting the link to the previous discussion, there was some very good comments there. I too have a cap on my vent line to stop the dripping to the floor, it was dripping like crazy. Hopefully this summer I will have everything re-worked and up to snuff in my boiler room.

Jamie Hall

Whatever one does, it is well to remember that the backflow preventer is a safety device. Not, perhaps, as dramatic as a pressure relief valve, but it is a safety device, nonetheless.

That means, among other things, that if it is dripping from the vent at least one of the check valves (the downstream one) is not closing properly, and for it to function as a safety device that valve must close.

My apologies for being a bit of a curmudgeon, but if the back flow preventer is dripping from the vent, either repair it so it doesn't or replace it.

A couple of other thoughts: it should never be used in a situation where the downstream pressure is routinely higher than the upstream pressure. That's an application for a checkvalve, not a BFP and especially not a RPZBFP.

If one has a situation where one has a downstream application, such as a boiler, which will remain pressurized when the upstream pressure is reduced (or drained), you must isolate the BFP with a valve between it and the pressurized application.

cutter

Jamie, I do have valves on both sides of the back flow preventer, they are gate valves.and they do not hold 100%. And both are shut off as tight as I can get them unless I am adding water to the system. I am going to change them to ball valves this summer if everything goes right.
To design a back flow preventer as finicky as these are doesn't make sense, unless they were to be designed as a cash cow as mentioned by another on here. What would be wrong if the valve had something like a needle valve and seat like in a carburetor. Instead of a float to close off the flow use a spring with enough tension to shut off the reverse flow but would be weak enough to allow line pressure to flow to the boiler. Years ago a swing check valve was allowed as a back flow preventer, never heard of anyone getting sick or dying from 12 PSI boiler water that leaked into a 50 PSI or better line. But then the valve was on the high pressure side of the swing check and the system was manual feed.
I feel that the manufactures could make a better valve that would be trouble free. That would prevent or stop people from doing what I did and others have done that are not heard about.

Jamie Hall

One can make better back flow preventers, and they are available commercially -- but more in the larger sizes. The overall concept isn't that hard, after all -- a really reliable check valve, a really reliable pressure reducing valve, and a really reliable check valve, piped in series, with a vent at the pressure reducing valve. But... to do that in a compact package at a consumer friendly price is a pretty tall order.

Does one really need one? That's one of those questions -- a lot of times, probably not. Codes tend to be pretty conservative (for which read "overkill")...

NY_Rob

Question...
I've had the classic Taco Taco Dual Unit Valve (http://www.supplyhouse.com/Taco-334-T3-Taco-Dual-Unit-Valve-Threaded-1995000-p?gclid=CJbd-fzI6MsCFQkfhgod5FsMYQ) unit on my boiler for years- I've had to shut off and drain my main water line to the house several times while making plumbing repairs, etc.
Even with no pressure from the main water supply the boiler has never lost system pressure or backfed into the domestic piping.
How are the new "back flow preventers" different than the old pressure reducer/feed valve combo?

Jamie Hall

Strictly speaking, that Taco is not a RPZ backflow preventer. If that is what is required, then this:
http://www.supplyhouse.com/Watts-0063030-3-4-Bronze-RPZ-009M3QT-2551000-p?gclid=CKaUho7Y6MsCFdgRgQod_qIDbQ
is what should be being used.
All too often this:
http://www.supplyhouse.com/Watts-0061888-9DM2-3-4-Brass-Dual-Check-Valve-with-Intermediate-Atmospheric-Vent?gclid=CPrZhN3Y6MsCFUgkgQod4-AItw
is used instead. Check the price difference...

ChrisJ

You could've at least linked to the lead free one Jamie.....

SWEI

It's also cast iron. They eventually rot out.

Jamie Hall

ChrisJ said:

You could've at least linked to the lead free one Jamie.....

I didn't want people to faint at the price...

RJ_4

check mine and others posts on Feb 2015 (leaking 009 backflow ) RJ

Hilly

Dual Check Valve with Atmospheric Ports (DCAP) are required for domestic heating boilers by AWWA standards as it is considered minor hazard. When a higher hazard exists due the use of chemical additives then a higher level protect is required and can be provided by installing a Reduced Pressure Principle Backflow Prevention Assembly (RP).

Hilly

Also if you have a vent port that 'spits' due to pressure fluctuations upstream you can install a soft seating check valve upstream of the BFP. Or if you use a lead free PRV that can be installed upstream of the BFP instead of the typical downstream and that should help reduce pressure jumps at the checks. DCAP's are designed for back-pressure and back-siphonage. So if functioning properly then shutting down your water supply should not be an issue. I can honestly say that since using Caleffi's combination units over the past 3 years I have never had to return to either for issues. (typical issues are vent's dripping, gaskets weeping at union connection). *knock on wood* They've proven to be a great product to me thus far.