Vapor/vacuum questions

Chris_83

I received some great help previously getting started  to understand my home's steam system ( <a href="http://www.heatinghelp.com/forum-thread/142756/Requesting-Help-to-Understand-and-Maintain-2-pipe-system">http://www.heatinghelp.com/forum-thread/142756/Requesting-Help-to-Understand-and-Maintain-2-pipe-system</a> ), and have a couple of questions about some next steps. 



Summary: The system was installed when the house was built in 1937, and apparently is a vapor/vacuum system.  Boiler is a Peerless JOT-5W installed in 1985.



Vaporstat - should I purchase a 0-1psi vaporstat or a 0-4psi model?  Will I want/need to set the system pressure above 1psi?  Or is it more important to have the finer adjustment capabilities of a 0-1 vaporstat instead?



Gauge - I will add a second, low-pressure gauge next to the vaporstat.  Since the system develops vacuum during the heating cycle, do I need to find a 3-0-3 psi gauge, or will a standard 0-3psi gauge be ok?



Backflow preventer - there is a Watts 9D backflow preventer installed between the fill valve and the boiler ( <a href="http://media.wattswater.com/ES-9DM3_M2.pdf">http://media.wattswater.com/ES-9DM3_M2.pdf</a> ) .  I replaced it a couple of years ago thinking it was defective, but that didn't solve the "problem".  After the thermostat is satisfied, there is a vacuum in the system, as confirmed by the 30-0-30psi gauge.  Then I can hear air being sucked into the boiler through the vent/drain of the backflow preventer and water drips out the same opening.  I can feel the vacuum and air movement by putting my thumb over the vent/drain opening.  I'm not sure how much vacuum there should be in the system, but this "reverse venting" brings the vacuum down to zero.  Is there a way to still have an inline backflow preventer but eliminate this problem?

icesailor

Watts 9D Backflow:

,,, 'Backflow preventer - there is a Watts 9D backflow preventer installed between the fill valve and the boiler ( http://media.wattswater.com/ES-9DM3_M2.pdf ) . I replaced it a couple of years ago thinking it was defective, but that didn't solve the "problem". After the thermostat is satisfied, there is a vacuum in the system, as confirmed by the 30-0-30psi gauge. Then I can hear air being sucked into the boiler through the vent/drain of the backflow preventer and water drips out the same opening. I can feel the vacuum and air movement by putting my thumb over the vent/drain opening. I'm not sure how much vacuum there should be in the system, but this "reverse venting" brings the vacuum down to zero. Is there a way to still have an inline backflow preventer but eliminate this problem? " ,,,

The Watts 9D backflow is installed improperly. It is on the wrong side of the fill valve. The function of the backflow is to protect the potable water system from backflow out of the boiler and into the potable water system. It belongs on the house side of the boiler feed. Not the other way around.

pipeking

THE BACKFLOW

 is just doing it's job by venting diferential presure. and yes it is sapose to be in between the autofeed and house,or u will have this problem always.

Chris_83

Backflow Preventer

There's a manual valve, not automatic refill.  The bf preventer is installed as shown in the pdf I linked to, but there is no 1156f regulator between the 9D and the boiler.  It looks like the regulator is meant to be used in a situation where the fill valve is left open all of the time ( http://s3.pexsupply.com/product_files/0386421-Install.pdf ) and the regulator's pressure setting controls the addition of water to the boiler. 

Jamie Hall

How's that again?

This is a steam boiler, right? In which case the water feed line is NOT left open all the time, with a pressure regulator.  That's for hydronic systems if it's ever used at all.



It sounds as though you have a manual fill valve, which can be used when the water level -- as seen on the gauge glass -- gets too low.  A nice arrangement, provided someone remembers to look at.  But whether you have a manual or an automatic feed, if your code requires a backflow preventer, it goes before the valves, not after (it should have yet another valve before it -- and at least one union, by the way, so that if it goes wrong you can fix it without having to drain the whole system!).



You don't need a pressure regulator, if it's steam.



You do need the vapourstat, and I would be inclined to use the 0 to 16 ounce for a vapour system.

Dave in QCA

Piping configuration

The normal piping configuration is to come from the city through a shut off valve, then through the back flow preventor.  Then on a steam boiler it is usual to go through the auto-fill device which usually has a fast fill valve paralleled to it.  Since you don't have a auto-fill, you still need a valve between the boiler and the back-flow preventor, otherwise when it sense a pressure lower than the atmosphere it's going to vent and break the vacuum.

Chris_83

Vacuum

So, is it possible that there is too much vacuum in the system and that is why air is sucked into the system through the backflow preventer?  This leads to another of my original questions - when I add a low-pressure gauge to the boiler, should I get one that reads vacuum also?  Would a regular 0-3 psi gauge be damaged by the vacuum pulling it below 0?

SWEI

If the backflow is in the wrong place

any vacuum at all will draw air into the system.

Charlie from wmass

If what you have is a vapor system

you need to remove the back-flow preventer.  I  checked your previous post for photos.

Chris_83

Backflow Preventer

The backflow preventer valve is installed as per the manufacturer's instructions, between the manual boiler fill valve and the boiler.

Dave in QCA

Explanation

Chris,

Here is the installation instructions from Watts.

http://media.wattswater.com/1910237.pdf

The diagram shown is for a water boiler, steam would be partly different.  First there should be a shut off valve upstream of the 9D as shown so that you can service and or replace the 9D if need be.  Downstream of the 9D, the drawing in the instructions shows a pressure reducing valve, which is an auto feed device for a hot water boiler.   In most steam boilers, the output of the 9D would be connected to an auto fill device.  The auto fill device is closed except when it is putting water into the boiler and thus the 9D is normally pressurised on both sides.  If for some reason you do not use an auto-fill device, then you MUST install a second shut off valve.  The valve upstream of the 9D should be left in the open position and the valve downstream should be used to fill the boiler and then should left in the closed position.   Thus, your manual operation would be simulating the same conditions that an auto fill valve would be producing.  The 9D will be pressurized, it will be separated from the boiler, and it will not be acting as a vacuum relief valve for the boiler.



Now, if by some crazy set of circumstances, you turn on the feed valve and the boiler is filling, then you leave momentarily, but fall on the stairs and break your leg... or for some other reason you become preoccupied and forget to go back to the boiler and close the valves....   And, at the same time, there is a HUGE rupture in the city main a block from your house and ALL pressure in the city system is lost.  And, at the same time, there are some points in the city system that are at a lower elevation than your house and the people who are trying to draw water in their house down the hill cause a negative pressure in your house, which tries to syphon water from your boiler through those valves that you left open....If all of those sequence of events happen, then That little 9D will then open and allow suction on the city side to draw air into your house pipes and on into the city pipes, and NOT draw water out of your dirty boiler into your house piping or the city mains.

Sorry for being windy, but I hope this helps you to understand

Chris_83

Fill Valve

Dave,



Thanks - your explanation makes sense.  I will add a second fill valve between the b/f preventer and the boiler, which will become the new "boiler fill" valve.