With my DIY hydronic system I am having problems with purging the system of air.

To give you an idea of the piping flows in my system:




Red = Diesel boiler
Green = Glycol storage tanks
Blue = Toe kick heater cores through out the bus, each with a separate feed and return.



The Toe kick heater cores do have a manual bleed valve at each core (In green box).

The diesel boiler really, really doesn't like any air bubbles in the coolant flow!!!

With our land yachts, we have a fair number of similarities to our boating brethren. They just run their engines for longer periods of time and use the waste heat for heating through out the boat. They then run the diesel boiler when they are at anchor and the main engines are shutdown.

In looking at a marine catalog they showed the following diagram.



Basically, their expansion tank also performs a degassing function so that the diesel boiler never sees any air in the system.

I queried the price of such a tank and the starting price was $300.00, hey a bit high for a single component.

I did a bit more research and there is a cheaper solution which is this tank:

https://www.butlertechnik.com/header...2-outlet-p1723

However, it only seems to be only available in Europe and it was kind of unknown how long it would take to get it. I did try to order from a web site that had a decent price, but they were unable to process either of my credit cards that I was willing to use.

Sent them an email and after a few days of no response I went looking for another solution.

Most automotive surge tanks have one big hose and smaller overflow hose. They are not constructed for the pass through degassing functionality that we need for our land yachts!!!

So anyway I started looking at various surge tanks on Amazon and the largest manufacturer of these types of tanks in the after market is a company by the name of Dorman. However their web site is totally oriented to the OEM replacement market that gives details on the vehicle that they are replacement parts for.

Absolution nothing about the hose sizes, etc. I did an online chat with one of their people via the web site and he was initially unwilling to help me, but hey I persisted:

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Kevin:
unfortunately ... unless you look at what tanks we already have available by vehicle, and give us specific numbers to look at hose sizes on them
Freds:
How about a 603-382 Coolant Reservoir?
Kevin:
let me pull the drawing one moment
Kevin:
unfortunately no good drawing for the nipple sizes
Freds:
How about 603-5201 Coolant Reservoir
Kevin:
ok so on that the lower hose nipple is 19mm and the od is 25.4mm
Freds:
Any detail on the uppers?
Kevin:
well they have metal inserts ... on the insert the ID is 18mm
Freds:
Thanks you very much for your assistance!!!
Kevin:
youre welcome
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So any way I called the local auto parts store and they ordered one into stock for me to look at the next day!



The lower outlet hose was one inch which was the same as my last tank and the other two hoses inlets were half an inch.