The 4d valve cuts off the expansion vessel in the open system.

Hello;

I am a few days before installing a new boiler in an old house. Installation is large diameter from the 70's steel, two-story house.
The new boiler also uses solid fuel.
The situation is complicated by the desire to install a 4d valve with an actuator.
The problem is that there is no extra pipe to the expansion vessel, but it looks like the vessel is connected somewhere upstairs to the heater return and only the overflow pipe returns from there.

The installation (of course, omitting the 4d valve and the common CH and DHW pump) now looks as follows:


Now the situation with the 4d valve: summer mode (or failure of the valve or control, or even the DHW priority) and the 4d valve cuts off the radiator circuit and the system becomes closed, ready to explode.
How to prevent it?
It is not possible to modify by adding a pipe to the vessel.

And how is the venting of the boiler and radiators currently carried out?

On the first floor I have all the new type aluminum radiators with a vent, on the ground floor there are only 2 old type steel radiators, from which, as well as from the boiler, I suspect the air is pushed out by the overflow vessel and heaters on the first floor.

Borek_PL wrote:

there are only 2 old steel ones on the ground floor, and from the boiler, I suspect the air is pushed out by the overflow vessel and heaters on the first floor.

It is not possible to bleed the system when the expansion vessel is located in the return. Unless you wrong, you drew it wrong.
Additionally, such a discharge of hot water from the boiler -> differential valve + pump bypass and above it a valve that may be accidentally closed.
The air that is released from the water during stronger heating, or the steam, should be easily vented, not through the pump.

The solution to your problem is simple. If you cannot add a new pipe to the vessel, move the vessel to the boiler room. Use an exchanger.
It can also be different. 3D temperature valve on the return to the boiler and the pump on the return. Thermostats for radiators. You do not touch the vessel (you only connect it from the power supply, not from the return), the boiler return temperature is protected and the rooms are not overheated.

@ stanislaw1954

Now the installation looks exactly like this:

When filling, the water rises through the return pipe and the supply pipe through the ball valve, the air escapes through the vents and the expansion vessel, this works so it is possible.
Granted, the valves can be accidentally closed and you can boil water by lightning, but everything can be spoiled if you try, only I can handle it. The bypass from the ball valve allows for easier discharge of impulse surpluses and relieves the pump (this is my reasoning)

@gersik
The first solution seems to be complicated and expensive and the exchanger certainly lowers the efficiency of the system.
However, the second - I admit that I like this direction, only the connection from the radiator to the vessel is in the bathroom under the tiles, so here the transformation is space. In addition, I wanted a higher CWO temperature - but if you let it go and keep the whole thing at higher temperatures ... - the house is not insulated and the higher temperature in the installation, it seems to me, will cool it down more due to the greater temperature difference wall - pipe .
Of course, my thinking and belief is classic that higher temperature in the installation means higher losses. The arguments about the lifetime of the boiler at higher return temperatures do not convince me, so far I had a Pleszew fine coal smack that worked on a 46-54 degree supply and has been living for 15 years until now, the only problem was silencing the fuel and a layer of tar in the boiler and chimney.

Thermostats are perfectly included in the conversion plans.

You can still bite it somehow because the solution seems to be close?

And the supply to the vessel from another place, e.g. from the second riser?

Borek_PL wrote:

The bypass from the ball valve allows for easier discharge of impulse surpluses and relieves the pump (this is my reasoning)

It's a bit wrong - bypass, it works in such a way that when the pump is not working, the whole thing goes straight up through the ball valve, but when the pump is turned on, the valve closes automatically (differential pressure before and after the valve).
Even though it all works (it can work), the deaeration of the boiler by the pump is unfortunately the most common cause of pump damage - seizure of the dry sliding bearing.

@gersik

There is no chance for the second pawn, but I came up with something ...



If we give a check valve, then any higher pressure in the boiler will be discharged vertically to the equalizing one, the danger is that the water will close in the circuit as I drew with the green arrow, because the temperature after the mixer (A) will be higher than in the return branch (B)
Does it have a chance to work?
Either way, the steady flow of the jets wavered and contrary to the principle that any elements along the way on the safety pipe could be mixed up with diameters, the return is 1.5 inch, if this fitting was made 1/2 inch and clipped into the second return in the boiler that would be unused. Probably the water will then choose the direction towards the top of the boiler instead of wandering along the pipes.

Contrived. Like a 4d valve is a safety pipe directly from the boiler.

You sculpt, and what's worse - not only is it dangerous, it also makes no sense. The painting from the first post is still the best, but you MUST move the expansion vessel into a thread that comes directly from the boiler. If you do not have a chance, then any later combinations are pointless, because you do not have the most important function preserved - the expansion is a fuse to prevent water from boiling in the installation, and as a water tank so that the installation has enough of it for proper operation, the second function (which you can implement e.g. by daily checking and manually topping up). Whatever you do - without an expansion expansion DIRECTLY at the outlet of the boiler, the installation will not be safe.

aniołek wrote:

- the expansion tank is a fuse preventing water in the system from boiling

You got it wrong.

The installation started two weeks ago and is operational;
The 4d (1.5 inch) valve was bypassed with a 1/2 inch pipe (green line in the picture) to the bleeding nipple - from the boiler's point of view, it is a direct connection via the return pipe to the expansion vessel (the cross-sectional area of the bypass is about 1/10 of the valve 4d). The pressure gauge shows a constant value, the pipe is sometimes warm, which confirms the correct operation of this solution.
On the other hand, the return temperature control also works very well, perhaps the characteristic of the stop angle to flow rate changes at large stopping down is slightly disturbed, but ultimately it is supposed to work on the actuator which will be controlled by temperature.
To sum up - maybe the "sculpture" does not comply with the regulations, but it solves the problem that can potentially occur when the valve is fully closed.

@_AnGeL_
I am not an expert in this industry, but logic and as the name suggests - expansion vessel (automatically ) replenishes water losses in the installation and its most important function in such a system is to prevent pressure increase due to the increase in the volume of heated water (changes buffering), and the boiler controller is used to prevent boiling of water - at least this is the case with me

The automation is actually supposed to protect against boiling, but the vessel is primarily to be a protection in the event of W. If it was only to refill water and change the volume when heated - on the way between the boiler and the tank, you could give different valves, 157 elbows, or finally - give a tube 1/4, because how much of this water is lost in everyday use? .. But the regulations (and, for example, the insurer) look at it differently - as few elbows as possible, the most gentle angles, no pumps or valves, and the diameter of the boiler at the outlet.
Personally, I am not interested in how you do it, but (which I do not wish you) you will see for yourself in the event of a serious failure - and the insurer will only be happy that he does not have to pay the cash ..

Borek_PL wrote:

and the boiler controller is used to prevent boiling of water - at least this is the case with me

As we know for a long time, "automatics" can fail and lead to disaster in the least expected time, so someone once invented a very simple way to secure the installation. This is the purpose of the safety pipe so that the steam accumulated as a result of boiling water has a free path outside the installation. You have neither a dog nor an otter. It is neither a safety pipe nor an expansion pipe.
This is your home and your installation so do what you want. It is a pity to write more because you know best.

The expansion vessel is not connected correctly. If something happens, you won't get a penny from the insurance.

The expansion vessel can be mounted on the return, but in this case the problem is the release of the steam that may be produced in the boiler in case of temperature increase.