expansion tank placement with Hydraulic separator and mod-con boiler.

Mike_Y

I'm finishing up the design portion of my new install. I'll be using a hydraulic separator to help keep costs down (it's a combo separator/dirt/magnetic unit with an air-vent on the top) and I'm finding conflicting info on expansion tank location. For clarity; I'm referring to the boiler side as primary, and CH loop as secondary. I've seen diagrams with the tank plumbed into the extra tapping on the Hydraulic separator, another where the tank is on the secondary loop attached to an air eliminator (what I always understood as THE place to have it) and in one case I found a diagram with the tank on the primary side. In all cases the circ is pumping away from the tank. My inclination is to put it on the secondary loop with the circ pumping into the loop and away from the tank which is connected to the system via a spirovent. Second question: is the spirovent redundant given that the separator has an automatic air-vent on it? Any input is greatly appreciated.

GGross

The "primary loop" just so you know, is whichever loop has the expansion tank piped on it. Generally your boiler pump will be on the return, pumping toward the boiler, which puts the return on the boiler loop, on the suction side of the boiler pump, as a fine spot to pipe an expansion tank.

hot_rod

Actually any of the 4 ports on a separator are workable. Either return port is ideal, cooler fluid.

Not straight below as it can collect crud on the diaphragm down there.

GGross

@hot_rod I think our OP may have been thinking of removing the plug and piping it to the well port in the center. I have seen this done before but if I understand correctly the threads there are straight threads, kind of surprised me to see when I walked onto a job and saw that.

Mike_Y

@GGross: you're correct, That was one of my possibilities. I don't have the separator in hand yet so wouldn't have known those were straight thread and not pipe thread. Thanks for that. And, no I would not have hung the tank from the bottom of the separator, that would negate the ability of flushing out the dirt/magnet sediment from the system. @hot_rod thank you for the diagram. Follow up: is the Spirovent I planned on carrying over from the old system redundant?

hot_rod

If it is a Caleffi 548 or 549 sep up to 2" size, that is a BSP straight thread. The plug has a gasket to seal. We do offer a temperature well that fits into that port.
I'd connect on the bottom, it looks cleaner and works best down low.

No need to have the Spiro.

EBEBRATT-Ed

@Mike_Y

Your hydraulic separator is the best air collection point there is. A "slow place in the road". A good air vent on that and your all set.