Air separator & backflow preventer

okhan

Hello. I'm new to posting but not new to reading the good info on this site. To give some background on the system I inherited four years ago upon moving into the home. Hot water boiler (Smith Cast Iron) monoflow system with two branches going to cast iron radiators.
There is a B&G control valve coming out of the boiler supply that is leaking. I was going to replace it but my plumber has told me that its no longer needed as the system has three zone valves and is pumped with a circulator. He stated that the control valve was for when there was only one gravity zone. Well my plumber is m.i.a. and finding a new plumber is not easy...well one that doesn't price gouge and actually knows the trade. I'm very proficient in fitting and soldering but its the placement that I want to nail down. I want to replace the control valve with Caleffi 1" sweat Discal vertical air separator. I know how to purge the system using the water feeder but I'm hoping this can be an upgrade as I currently have no air purging equipment other than bleeders on the rads. I've included photo's of the control valve. It comes right off of the boiler supply and splits to the expansion tank and then to the zone valves. Is this a good spot? The other component that I would like to install is a backflow preventer. Just a simple sweat one. This can be installed right before the water feeder correct? I would like to thank anyone for taking the time to read this and if you can help it would be much appreciated.

Zman

I think the flow check can go away.
I am guessing that your circulator is on the return pumping towards the boiler and expansion tank. If this is the case, the expansion tank and fill assembly should be on the return side, before the circulator.

Do you have an air eliminator somewhere?
It looks like you have 2 pressure-reducing valves and no backflow preventer.

You might as well clean it all up if you are going to drain it down and grab the torch.

HVACNUT

@Zman, that's actually 1 B&G PRV, and 1 old Taco 30 lb relief valve. 
My concern is on the mono flo loop, the water feed is above the purge station. Hence the need to bleed from the rads on that loop. The 3/4 loops will purge fine as long as the 1 inch zone valve is closed. The diaphragm tank is on the supply and the feed and circulator are on the return. 
Save your project for spring and repipe the whole thing.

EBEBRATT-Ed

Good comments above by all. @Zman is correct. With zone valve the flow check is not needed

Zman

@HVACNUT, good catch on the relief valve. Assuming that the one on the boiler is rated for the capacity on the boiler, I would cut the Taco out and install a backflow preventer (on the upstream side).

okhan

It seems like the system is incorrectly piped because I'm pumping towards the expansion tank. What if I moved the circulator pump to the supply side after the expansion tank? Where would the best place in the system be for the city water to enter. Right now it's on the return.

mattmia2

Same place as the expansion tank but it doesn't mater a whole lot for the water feed. The circulator, expansion tank, and air separator being in the right orientation are a lot more important.

okhan

Yeah I think I'm going to move the circulator pump to the supply side and add the air separator. I'll do this project in the spring. At some point in the next 5 years I want to change the boiler. The Smith is a workhorse but its so loud. Its a converted oil burner and when its running the whole house knows...the basement is the boiler room on the Titanic lol!!

EBEBRATT-Ed

@okhan

The Smith series 8 have proven to be good boilers. I wouldn't change it if it's not leaking. It's better than most

HVACNUT

You can eliminate the Taco relief valve by the PRV because there's also one on the boiler. Replace that one while doing the other work.

okhan

Hvacnut, is it god practice to replace them periodically. The boiler does have a 30lbs prv built into it and too my knowledge it has never been replaced. Good to know about the Smith boiler being a performer, it hasn't given me any issues. The Taco prv will be eliminated.