Each plumber installing a heating system installs an expansion tank in a specific place according to the project. And if it is not there, then on the basis of experience and some information, it makes an installation in the place where it pleases.
In this article I tried to compose opinions on this controversial issue, made colorful illustrations.
But first, I will explain what the expansion tank is for:
This device compensates for the increase in the volume of the coolant when it heats up, protects the system from overpressure and compensates for minor leaks.
Where to put the expansion tank. In front of the circular pump (3), after it (2) or in the flow of the heater (1)?
This dilemma is faced by many installers. If we turn to some documents, then this question, partially and indirectly, is answered by CODE OF RULES 282.1325800.2016
Apartment heating systems based on individual gas heat generators. Design rules and devices
8.10 At the inlet of the supply and return pipelines of the heating system to the heat generator, stop valves should be installed. It must not be placed between the heat generator and safety devices (safety valve, expansion vessel, etc.).
These rules do not apply to private homes. But according to them, the location of the tank should be either after the boiler to the shut-off valves (1) or in front of the boiler, in front of the shut-off valves (2).
And this position of the tank, if you follow the logic, serves not only for compensating expansion of the coolant in operating mode, but also for protecting the boiler from overpressure in case of an emergency, but in fact it will not help much, when the boiler goes into "runaway", its volume is sufficient is small, therefore, a safety group or a safety valve should be installed, which will discharge excess energy from the kennel, thereby protecting system.
Options 1 and 2 in the illustrations are not optimal, maintenance of expansion vessels with such a connection, without shut-off valves, leads to difficulties. Such as stopping the system when replacing or servicing the tank, draining the coolant from the communicating cavities to the stop valves.
Installing an expansion tank in front of the circulation pump
This option for installing a circulation pump is the most optimal. Knowledgeable plumbers try to "stick" just in front of the suction line of the pump:
What is the reason for this? It is considered, and as practical experiments show, when the pump is not running and when the pump is running, the entry point of the branch pipe is from expansion tank into the system, it always remains at a constant static pressure of the system, due to the operation of the expansion membrane tank.
If the expansion vessel is installed directly under the suction inlet, then the system vacuum section will be minimal.
And if the expansion tank is installed after the pump, then the vacuum section will increase over the entire length of the system.
What can this factor lead to?
To nothing, this factor is not terrible when the system has a stable working pressure. 1.5-2 BAR. In this case, it does not matter where to install the expansion tank, before or after the pump, and at what distance.
But if the pressure in the system begins to drop and the expansion tank installed after the pump will aggravate the situation, further lowering the pressure. And to lose sight of this moment, or the automation does not work, then when the pressure drops, air can be captured from air vent, which can lead to system shutdown, increased noise, cavitation effect occurs on the blades circulator, destroying it. And also the system is subject to increased corrosion due to freshly supplied oxygen.
As a result, if there is a need to turn on "foolproof", then be sure to install the expander tank in front of the pump at the minimum area. Well, in open systems, where the pump crashes, this condition is mandatory.