Q about backflow preventer on inlet water line

Reply

  #1  
Old 02-18-13, 06:32 AM
Member
Thread Starter
Join Date: Nov 2007
Location: MI
Posts: 2,612
Received 0 Votes on 0 Posts
Q about backflow preventer on inlet water line

The fill water inlet on my boiler is plumbed from a globe valve through a backflow preventer, through a pressure reducing valve and then into the boiler hot water outlet pipe. I just bought this vacation home last August and on my visits there I have been learning--and fixing--many odd things with the boiler. Most of this winter I have had a slight leak of system fluid from the backflow preventer vent (or is it a drain?). Not much--about 16 ounces in 6 months. Under what conditions does this valve discharge fluid? My system is filled with (I think) ethylene glycol so as an added precaution against cross-contamination I have been leaving the fill valve shut off. I've seen this recommendation many times but is this why I'm getting a glycol discharge from the backflow preventer?

To head off some likely follow-up questions: System pressure is 12psi as read on a known-good gauge attached to the drain. Pressure never varies more than 2psi cold/hot, fill valve on/off. There are no other leaks that I know of.
 
Sponsored Links
  #2  
Old 02-18-13, 06:49 AM
NJT's Avatar
NJT
NJT is offline
Member
Join Date: Oct 2006
Location: USA
Posts: 23,539
Received 1 Vote on 1 Post
Those backflow preventers are not the most 'reliable' devices in the world.

I've never been able to grok exactly how they are supposed to work, but there is definitely some sort of differential pressure mechanism at play.

I've seen documents that discuss testing the functionality of them and they all have diff gauges connected across them. (the commercial versions actually have ports for connecting these test sets)

Bottom line is that one or more of the 3 check valves inside the BP is 'weeping'. Either a worn sealing face, or a piece of 'crud' under the valve seat.

They are connected via union connections and can be easily removed. They can also be disassembled for cleaning. You may need new flat face union washers and some O-rings if the orignals are unusable. The union washers can be 3/4" water meter washers... same size.
 
  #3  
Old 02-18-13, 10:14 AM
Member
Thread Starter
Join Date: Nov 2007
Location: MI
Posts: 2,612
Received 0 Votes on 0 Posts
Will the PRV prevent fluid from escaping while I remove the BP?
 
  #4  
Old 02-18-13, 10:25 AM
Member
Join Date: Dec 2010
Location: USA
Posts: 332
Received 0 Votes on 0 Posts
NJ Trooper,

I think the fact that back flow preventer has a discharge port means that they are designed to let water out and it's not necessarily indicative of something being worn out or contaminated. I wonder if it's designed to let water out if there is any back flow pressure that exceeds some threshold.

As I mentioned in my previous post (http://www.doityourself.com/forum/bo...-troubles.html) I currently having problems with pressure reducing valve. It's not reducing any pressure and I think its check valve functionality is gone as well. So now my cold water intake is closed and back flow preventer is constantly seeping water so the whole system is loosing pressure.

I'm waiting for heating system to be over to replace the pressure reducing valve. For now I actually plugged the discharge port of the backflow preventer with a rubber plug and it stabilized the system at 8 psi. There is no risk of contamination since the intake is closed and I will flush the system when I replaced the valve.

So I'm limping alone till spring I might replace the back flow prventer for good measure as well.

As for original post, I wonder if you have problems with pressure reducing valve as well and possibly with expansion tank. During pressure raise in the system, if pressure reducing valve allows for system liquid to pass back upstream, the back flow preventer would most likely discharge it. Just a thought.
 
  #5  
Old 02-18-13, 11:07 AM
NJT's Avatar
NJT
NJT is offline
Member
Join Date: Oct 2006
Location: USA
Posts: 23,539
Received 1 Vote on 1 Post
Will the PRV prevent fluid from escaping while I remove the BP?
Most have check valve built in... but I don't know that I would trust it... I wish all installers would think to install valves both UP and DOWN stream of the reducing valve and BFP for this reason.
 
  #6  
Old 02-18-13, 12:01 PM
Member
Thread Starter
Join Date: Nov 2007
Location: MI
Posts: 2,612
Received 0 Votes on 0 Posts
At some point in the near future I'm planning to cut into the system & move some baseboards so a flush & refill will be done at that time. Til then I'm sort of limping along as well. So let's say I want to remove the BP and I loosen the unions to see if it holds water. If it does spurt how can I put it back in? I don't want to dilute my freeze protection just yet by adding clean water through the fill valve. Seems like I've seen mention of a hand-operated piston pump you can use to pump from a bucket in through the drain spigot--but I've never seen a picture or a product recommendation.
 
  #7  
Old 02-20-13, 04:56 PM
NJT's Avatar
NJT
NJT is offline
Member
Join Date: Oct 2006
Location: USA
Posts: 23,539
Received 1 Vote on 1 Post
I think the fact that back flow preventer has a discharge port means that they are designed to let water out and it's not necessarily indicative of something being worn out or contaminated. I wonder if it's designed to let water out if there is any back flow pressure that exceeds some threshold.
If it drips from the atmospheric vent port, it DOES mean that one of the check valves is leaking.

There is no sort of 'threshold' ... ANY backflow is to be stopped, not only after some threshold.

See:

http://www.backflow-supply.com/backf...atts/is-9d.pdf

This one has a cutaway view showing the 'shuttle valve' and the checks.

http://media2.wattswater.com/ES-9DM3_M2.pdf
 
  #8  
Old 02-21-13, 08:13 AM
Member
Join Date: Dec 2010
Location: USA
Posts: 332
Received 0 Votes on 0 Posts
i was thinking that if there is any backflow past first check valve maybe it will start draining to prevent water go past the second check valve. i didn't imply that some backflow was "allowed".

but it looks like i was wrong. so i guess BFP gets replaced when i replace the PRV.
 
  #9  
Old 02-21-13, 08:22 AM
Member
Join Date: Jun 2012
Posts: 894
Received 2 Votes on 2 Posts
From the Watts instructions:
Quick closing valves, water hammer or supply pressure fluctuations can cause intermittent discharge
One would assume that a small discharge now and then (intermittent) would indicate the valve is doing it's job.

A continuous discharge or drip would indicate an issue like excessive water hammer, pressure fluctuations or indeed a valve in need of repair/replacement.

One
[quote]
 
  #10  
Old 02-21-13, 09:12 AM
Member
Thread Starter
Join Date: Nov 2007
Location: MI
Posts: 2,612
Received 0 Votes on 0 Posts
I wonder what they mean by "pressure fluctuations"? I'm on a well so my pressure fluctuates constantly--but not suddenly. Also since I keep the fill valve shut off the pressure on that side of the BP could over time drop to zero as the PRV lets in make-up water. That was my original concern--if the supply side drops to zero will the BP & PRV valves malfunction?
 
  #11  
Old 02-21-13, 09:20 AM
Member
Thread Starter
Join Date: Nov 2007
Location: MI
Posts: 2,612
Received 0 Votes on 0 Posts
Good find on the Watts diagram, thanks Trooper. That may be my very model. Really helps to understand its function (but I'm hoping the "outlet" in the diagram is actually the inlet--otherwise the checks are always pressed closed).
 
  #12  
Old 02-21-13, 02:48 PM
NJT's Avatar
NJT
NJT is offline
Member
Join Date: Oct 2006
Location: USA
Posts: 23,539
Received 1 Vote on 1 Post
I'm hoping the "outlet" in the diagram is actually the inlet
I believe that it is... know for a fact that the strainer screen is on the inlet.

If you've got the manual shutoff ahead of the valve closed, and it's dripping, it means that the 'secondary' check is leaking a wee bit.
 
  #13  
Old 02-22-13, 06:43 AM
Member
Thread Starter
Join Date: Nov 2007
Location: MI
Posts: 2,612
Received 0 Votes on 0 Posts
Is this a sensible idea?
After the water supply globe valve I install a tee and mount a small expansion tank & gauge. Open the supply valve to charge the tank, then close the valve. This positively isolates the boiler nasties from my potable supply yet keeps the system pressurized so it can get make-up water & the BP & PRV will work as intended.

Or am I getting too Rube Goldberg here?
 
  #14  
Old 02-22-13, 08:53 AM
NJT's Avatar
NJT
NJT is offline
Member
Join Date: Oct 2006
Location: USA
Posts: 23,539
Received 1 Vote on 1 Post
I don't think it's nonsensical... but probably overkill.

Fact is that even if you installed the tank, and maintained pressure on the BFP inlet side, it might/could still leak...
 
  #15  
Old 02-22-13, 11:49 AM
Member
Thread Starter
Join Date: Nov 2007
Location: MI
Posts: 2,612
Received 0 Votes on 0 Posts
This isn't to remedy the leak--though it might as a side benefit of keeping pressure on both checks. Just a way to have make-up water available, but in limited amounts (in case of leak) and isolated from the potable supply. Sucks trying to CYA in an uninhabited house.

This leak MAY have existed for years...I've noticed the white vinyl tile in the mech. room is a little green around the boiler.
 
  #16  
Old 02-22-13, 02:27 PM
NJT's Avatar
NJT
NJT is offline
Member
Join Date: Oct 2006
Location: USA
Posts: 23,539
Received 1 Vote on 1 Post
I sure wish I could find one of those animated 'flash' presentations that show exactly how the BFP operates. It's hard to grok by looking at the cutaway. I've got a couple in my recycle bin, I might have to take one apart this weekend.

I guess it's a good idea to add the tank... not going to help with a 'gross' leak, but just a wee drip, it might keep the pressure up on the system... and it actually might help the BFP drip too... I'll know more after I autopsy one.
 
  #17  
Old 02-23-13, 10:52 AM
Member
Thread Starter
Join Date: Nov 2007
Location: MI
Posts: 2,612
Received 0 Votes on 0 Posts
I appreciate the help & advice. Next time there I'll look for a model number & maybe order a maintenance kit if available.

Fortunately the leak is minor so there's no need to rush a repair. With what I've learned here I've been able to change the wiring & settings of my controls & limits so the system is actually working correctly--maybe for the first time in years. Man was it screwed up!
 
  #18  
Old 02-23-13, 01:18 PM
NJT's Avatar
NJT
NJT is offline
Member
Join Date: Oct 2006
Location: USA
Posts: 23,539
Received 1 Vote on 1 Post
I just finished my dissection of one of the old valves I have and have a much clearer understanding of how it works now.

I'm going to see if I can draw something up that makes more sense than the cutaway in the Watts brochure.

I don't really think that it makes a heckuva lotta sense to disassemble and clean an old valve after taking this one apart. Unless of course you are REALLY frugal. The rubber washers and things in this valve are pretty hard and dry and it's only about six years old. Given that there are flat union connections on both ends, it's probably best to just go ahead and replace a leaking one. The rebuild kits I've seen (IF you can find a place to purchase them) cost nearly what a new valve costs.
 
  #19  
Old 02-23-13, 02:31 PM
NJT's Avatar
NJT
NJT is offline
Member
Join Date: Oct 2006
Location: USA
Posts: 23,539
Received 1 Vote on 1 Post
Here's what I've come up with. It makes sense to me, let's hope it does to others as well!

Name:  WATTS 9D BFP WORKS.jpg
Views: 8698
Size:  28.2 KB

Primary check valve A seals against diaphragm C.

Diaphragm C seals against inner water passage D.

Secondary check valve B seals against inner water passage D.

When inlet pressure is present, diaphragm C is held against inner water passage D and seals atmospheric chamber E.

If inlet and outlet pressures are equal (in normal operation they will be) diaphragm C will seal against atmospherice chamber E and water can flow freely through A and B as needed.

If inlet pressure drops below outlet pressure, secondary check valve B will seal against backflow... UNLESS valve B leaks, in which case inner water passage D will pressurize and push primary check valve A against diaphragm C which will open to atmospheric chamber E. (Guy, this is your case...)

It's not 'perfect'... let's say that inlet pressure 'goes away' and there is a gross leak between A and C, AND B is also leaking. In spite of the atmospheric opening it would still theoretically be possible for backflow to occur, but VERY limited, and VERY unlikely. It would have to be a 'perfect storm' for all these things to occur at one time.

Anybody have any more scenario?
 
  #20  
Old 02-23-13, 04:00 PM
NJT's Avatar
NJT
NJT is offline
Member
Join Date: Oct 2006
Location: USA
Posts: 23,539
Received 1 Vote on 1 Post
For fans of 'color coded' graphics, I added (and improved) the Watts graphic and colored the various areas.

Name:  WATTS 9D BFP WORKS.jpg
Views: 11747
Size:  41.2 KB

I've got too much time on my hands...
 
  #21  
Old 02-23-13, 06:15 PM
Member
Thread Starter
Join Date: Nov 2007
Location: MI
Posts: 2,612
Received 0 Votes on 0 Posts
That "C" is a flexible seat is a surprise--and explains a lot. The earlier diagram shows this open, so it would flow to Vent all the time. Thank you very much for the new diagrams--I really am obsessed with knowing how things work.

I suspect you're right on the cost to repair vs. replace. I've noticed Watts BP + PRV combo packages are almost the same price as either one separately. The inspection sticker on my boiler is 1994 and in all the home receipts I have there are no service receipts more recent. As messed up up as the wiring & limits settings were, I don't think a pro has seen it in a LONG time.
 
  #22  
Old 02-23-13, 06:21 PM
NJT's Avatar
NJT
NJT is offline
Member
Join Date: Oct 2006
Location: USA
Posts: 23,539
Received 1 Vote on 1 Post
That "C" is a flexible seat is a surprise
To me too... In all my imaginings, I couldn't mentally visualize how this thing could possibly work. The second I pulled that part out it all came to me in a blinding flash.

I really am obsessed with knowing how things work.
You and me both... I learned a long time ago that you can't possibly troubleshoot something without knowing how it's SUPPOSED to work, and WHY it works the way it does.

That, and "...troubleshooting is 99% VISUAL..."

The BFP has been on my list of things to learn more about for a LONG time, thanks for the 'push' to gitter done.
 
  #23  
Old 02-24-13, 10:27 AM
Member
Join Date: Dec 2010
Location: USA
Posts: 332
Received 0 Votes on 0 Posts
NJ Trooper, thanks for putting time and effort into this, it's good info!
 
  #24  
Old 06-01-13, 11:52 AM
Member
Join Date: Dec 2010
Location: USA
Posts: 78
Received 0 Votes on 0 Posts
So C or B if not sealing properly or stuck (B) could let water pass into the vent chamber and out the vent tube?
Thanks for bringing this up! I just noticed last night that my BFP is leaking, for the first time I believe. I was wondering if I should be concerned. Should I just keep an eye on it?
BTW, boiler pressure at the time was 18 psi. Boiler is in use for domestic hot water.
 
  #25  
Old 06-01-13, 07:56 PM
NJT's Avatar
NJT
NJT is offline
Member
Join Date: Oct 2006
Location: USA
Posts: 23,539
Received 1 Vote on 1 Post
If water is leaking out the vent, it has to be leaking past C.

C will only be opened 'on purpose' if B leaks, AND pressure on outlet side is higher than on the inlet side. This will cause A to seal against and push C open.

If your BFP is properly installed upstream, on the domestic side of the pressure reducing valve, the pressure on inlet and outlet should be roughly the same so if you've got a slow continuous drip, it is most likely that the C seal is simply leaking.

It's not something to 'worry' about in that you might have backflow into your domestic, and the leak probably won't get worse quickly, but I would plan on changing it out if it were my system. Not an emergency though...

It may in fact stop leaking all on it's own, but still, I would plan on changing it at some point.
 
  #26  
Old 06-02-13, 07:32 AM
Member
Join Date: Dec 2010
Location: USA
Posts: 78
Received 0 Votes on 0 Posts
The BFP in installed properly. I checked again and there's a little puddle there but I haven't actually seen water come out. I have very hard water (well), so that might be the problem. BTW, what does "intermediate" mean? That's in the name on the plate on the valve.
Thanx!
 
  #27  
Old 06-02-13, 08:04 AM
NJT's Avatar
NJT
NJT is offline
Member
Join Date: Oct 2006
Location: USA
Posts: 23,539
Received 1 Vote on 1 Post
Hard water can be a problem in addition to the fact that if you have any 'solids' coming from the well and no or minimum filtering ahead of...

With city water there is not much chance of water pressure dropping below boiler pressure, but with private well (I'm on one too) the chance is much greater.

what does "intermediate" mean? That's in the name on the plate on the valve.
Not sure... in what context is it used?

The intermediate chamber is the one in the middle in the diagram.

What's the make/model of your BFP?
 
  #28  
Old 06-02-13, 09:00 PM
Member
Thread Starter
Join Date: Nov 2007
Location: MI
Posts: 2,612
Received 0 Votes on 0 Posts
Just to update my situation I haven't leaked a drop since I shut off the make-up water supply valve. My BFP only discharged water when the valve was open *and the supply pressure dropped below boiler pressure*. That was every time I left my cottage for more than a day. (I've since found I have a leaking toilet valve to explain the fall in pressure when I shut off the pump--which I do every time I leave)

In a sealed and non-leaking hot water boiler system there's no reason to leave the supply valve open--and it's often advised against leaving it open if you have a glycol-filled system like I do. I just keep an eye on the system pressure and somewhat grudgingly trust the low-water sensor to prevent a major problem.

This water discharge must have dogged the previous owner too since the white tile on the floor around the boiler has a slight green tint (from the glycol).
 
  #29  
Old 06-03-13, 09:10 PM
Member
Join Date: Dec 2010
Location: USA
Posts: 78
Received 0 Votes on 0 Posts
Regtrol (which I believe is made by Watts) Back Flow Preventer with Intermediate Atmospheric Vent. I don't have any pressure problems, but the water has a lot of calcium & manganese which if any air is allowed to the valve would cause a buildup of deposits in the valve. Seems to be letting more water out now so I'll replace it if that's not the normal function and I'll dissect it and see what happened.
 
  #30  
Old 08-23-13, 10:36 AM
Member
Join Date: Dec 2010
Location: USA
Posts: 78
Received 0 Votes on 0 Posts
No more water leaking out now. I don't know if that's good or bad (?).
 
  #31  
Old 08-23-13, 03:58 PM
NJT's Avatar
NJT
NJT is offline
Member
Join Date: Oct 2006
Location: USA
Posts: 23,539
Received 1 Vote on 1 Post
Hi MrPop, I think no leak is always a good thing! Just keep an eye on things and if it becomes a bothersome leaker again, change it out...
 
  #32  
Old 08-23-13, 08:05 PM
Member
Join Date: Dec 2010
Location: USA
Posts: 78
Received 0 Votes on 0 Posts
Thanx, didn't know if it would cause a pressure problem or not do what it's supposed to do.
 
Reply

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Thread Tools
Search this Thread
Display Modes
 
Ask a Question
Question Title:
Description:
Your question will be posted in: