3 Way valve, open vented commercial boiler.

in my experience the flow should never be valved, I would make a header from 2 inch 3 inch or 4 inch pipe so the boilers input to that header, then feed the zones using motorized valves controlled by stats in the areas they are heating,

They'll not be obstructing the vent (expansion pipe) DD.
It may have valves on the flow pipe from the boiler but the main route of the vent pipe to the tank will be direct  without any valves.

I'm trying to get my head around Clart's system. Any pictures Clart?

The manual 3 way valve sounds very interesting....something to close down a boiler when the systems not at full capacity perhaps?  

On further investigation, ( I rang my Dad, AKA Pappa Clart) the 3 way valves are used so that you can isolate the the water supply to the boiler so one can carry out maintenance on the appliance. Papper Clart informed me that a pressure relief valve was required before the 3 way valve just incase the worst case scenario occurred and the open vent was in the closed position. There are 2 PRVs installed on each boiler.

I'll take some photos tomorrow but I'm not sure how to share them on here?

I've not had much experience on large commercial boilers Clart.
However, I think that that's what's called a "blow down valve". Is it steam heating?
If so, it's for relieving a build up of pressure which you do manually with a key that you open up when required. It's connected to a discharge pipe normally leading outside to discharge the steam in a safe place.


The one I'm remembering went under the floor in the boiler house and then discharged over the canal.
The pipe was rotten though and a load of steam would be released upwards into the boiler house whenever you operated it.

We could play a trick on anyone entering the boiler room (if we was quick enough), we'd hear the door catch click wait a few seconds for our victim to get in the right spot then discharge it just as our visitor was directly over the rotten pipe area under the floor; if out timing was right we'd cover our visitor in a upwards blast shower of steam.

NB I was caught out by this quite a few times before the penny finally dropped !

Oh OK, I'm really out of my depth on this one Clart.

That flange joint does give it a way that it's more of an industrial than Domestic plumbing job.

It could still be for the manual release of air/pressure from the system though.

Does that vent pipe/release pipe from the valve lead to the outside?


 

Get him on he's probably fountain of knowledge Clart.