Why Hydraulic Separator are made from steel for high header loss condensing boilers?

magnetite or hematite can only form with oxygen present. So unless O2 is entering the fill water becomes oxygen starved within days.

A quality separator would have a microbubble air eliminator inside to speed air and microbubble removal. A good sep should be high 90% efficient for air removal. As well as other features to protect the system.

Seperators are sized or should be by the velocity in the center barrel. If you want additional fluid capacity a small buffer tank is an option. We see wall hung buffer tank versions in the 7-21 gallon range available now.

Most hydronic tanks are steel, circulators cast iron.

A hydronic conditioner additive is another good step to protect all the multiple metals in a system, and they include oxygen scavengers.

It is possible to build an entirely non ferrous hydronic system, and is ocassionally done on non barrier hydronic tube systems.

oxidation can only occur with o2 and the electrolyte

It is tough to keep O2 out of a closed loop hydronic system

Mother nature hates all imbalances, temperature, pressure , moisture, so if there is a o2 starved condition, it will try to balance that, o2 squeezes in.

The oxygen barrier on hydronic pex only slows oxygen ingress. Same as the EVOH o2 barrier on plastic milk jugs.

Higher fluid temperature attracts more o2 ingress, so 180 degree systems are more prone to oxygen ingress.

The original rubber hydronic tube was an O2 sieve. It could destroy high temperature ferrous systems in a years time, expansion tanks were the first to fail. That’s the sludge in the bottom of your ci boiler 🫢

Oxygen, at the molecular level can enter through pump seals, valve packings, pex tube,

And Im wondering how 02 tight press fittings are???

You see that green fuzz on some press fittings?? Something is going in and out through the o ring causing that?

So my systems get hydronic conditioner like Fernox, cheap insurance in my mind. It has oxygen scavangers, ph balance, snd a film provider to protect all the metals from attact, similar chemicals are in hydronic glycols.

Other than cost I see no reason against an overdized sep,

. A buffer tank can act as a sep. It creates that low velocity zone that is key to separation.

Here is the math on Caleffi seps

The barrel is 9A, nine times the size (area) of the connections, on smaller sizes that is about 3-1, so a 2” sep would have a 6” barrel.

The goal is flow velocity top to bottom near zero.

I have tested some brands of seps that don’t separate ! The barrel size is too small and fluid blasts across.

Have you priced a stainless circulator? That is one reason non ferrous hydronics are not common