8
2.4 - SYSTEM ACCESSORIES
EXPANSION VESSEL
In operation, the volume of oil in circulation varies due to the
temperature changes.
The increase in diathermic oil volume is around 7% for a tem
-
perature increase of 100°C.
This involves the need to absorb the oil expansions by inserting
an expansion vessel in the circuit.
It is good practice that, with system cold, the
oil occupies at least 1/4 of the expansion ves
-
sel capacity to ensure an appropriate seal
and, with system hot, does not exceed 3/4 of
the tank capacity to prevent any overflow.
If it is assumed that the system features are such to make it dif
-
ficult to maintain a temperature sufficiently low in the expansion
vessel (60 - max 70°C at temperature), we recommend provid
-
ing a heat sink on the connection pipe of the expansion vessel.
The expansion vessels used are mainly of the open type (at
-
mospheric): in this case, they will be placed at a height, so that
the minimum level exceeds the max level reached by the system
or the utilities, by at least 1.5 m.
The minimum height, subject to exceptions to be examined
case by case, will be such to ensure a 6 m seal at least on the
intake axis of the circulation pump.
It will be placed preferably in a ventilated area to avoid the tem
-
perature increasing excessively and protected against water
infiltration.
When wanting greater pressures in the system, or it is not pos
-
sible for some reason to place the vessel at an adequate height,
be it only for aesthetic reasons, you can place an expansion ves
-
sel in the boiler room, of the pressurised type. This vessel will be
pressurised with nitrogen, using cylinders and decompression
station, and equipment with the necessary safety devices.
The connection pipe to the expansion vessel:
- must be free of shut-offs
- must be such to prevent convective motions of the oil
- must not be insulated.
DIATHERMIC OIL COLLECTION TANK
It is a simple container with a higher capacity than the total of
the system.
It must be placed outside the boiler room, preferably outdoors
and in ventilated premises protected from rain, in pit below
ground level not buried, on floor, or raised.
If buried, it will be necessary to also adequately lower the load
-
ing height to avoid intake problems.
In case of landfill, it is mandatory to use a double-wall vessel as
provided for all flammable liquids.
The system loading pump, with its group of valves, is located
near the oil storage tank.
SYSTEM LOADING UNIT
It consists in a gear pump coupled to an electric motor, com
-
plete with two-way steel valves.
It must be placed in a position protected from rain and level with
the collection vessel, in order to facilitate the intake of the pump.
OIL CIRCULATION PUMP(S) UNIT
They are normally single-state centrifugal pumps coupled to the
motor through a elastic joint.
Everything is assembled on the base which ensures alignment
of the components.
The pump seal is of the air-cooled type.
SHUT-OFF VALVES
The shut-off valves for diathermic oil systems must have a sphe
-
roidal cast iron body and be fitted with bellow seal.
DIATHERMIC OIL FILTER
Upstream of the circulation pump(s) install a filter for diathermic
oil with spheroidal cast iron or steel body and with a large mesh
filter basket.
EXPANSION COMPENSATORS
The expansion compensators must be installed to absorb the
axial expansions of the pipes due to high operating tempera
-
tures.
The pipes must be suitably bracketed so that the compensators
can perform their function without the burden of any weight that
might cause misalignment between the jointed pipes, leading to
possible failure of the bellows and leaking of oil.
