Venting pipes to the expansion tank are to be installed at all high points in the piping system,
where air or gas can accumulate.
The vent pipes must be continuously rising.
9.3.11
Expansion tank (4T05)
The expansion tank compensates for thermal expansion of the coolant, serves for venting of
the circuits and provides a sufficient static pressure for the circulating pumps.
Design data:
70 - 150 kPa (0.7...1.5 bar)
Pressure from the expansion tank at pump inlet
min. 10% of the total system volume
Volume
NOTE
The maximum pressure at the engine must not be exceeded in case an electrically
driven pump is installed significantly higher than the engine.
Concerning the water volume in the engine, see chapter Technical data.
The expansion tank should be equipped with an inspection hatch, a level gauge, a low level
alarm and necessary means for dosing of cooling water additives.
The vent pipes should enter the tank below the water level. The vent pipes must be drawn
separately to the tank (see air venting) and the pipes should be provided with labels at the
expansion tank.
Small amounts of fuel gas may enter the DF-engine cooling water system. The gas (just like
air) is separated in the cooling water system and will finally be released in the cooling water
expansion tank. Therefore, the cooling water expansion tank has to be of closed-top type, to
prevent release of gas into open air.
The DF-engine cooling water expansion tank breathing has to be treated similarly to the gas
pipe ventilation. Openings into open air from the cooling water expansion tank other than the
breather pipe have to be normally either closed or of type that does not allow fuel gas to exit
the tank (e.g. overflow pipe arrangement with water lock). The cooling water expansion tank
breathing pipes of engines located in same engine room can be combined.
The structure and arrangement of cooling water expansion tank may need to be approved by
Classification Society project-specifically.
The balance pipe down from the expansion tank must be dimensioned for a flow velocity not
exceeding 1.0...1.5 m/s in order to ensure the required pressure at the pump inlet with engines
running. The flow through the pipe depends on the number of vent pipes to the tank and the
size of the orifices in the vent pipes. The table below can be used for guidance.
Table 9-1
Minimum diameter of balance pipe
Max. number of vent pipes
with ø 5 mm orifice
Max. flow velocity (m/s)
Nominal pipe size
3
1.1
DN 32
6
1.2
DN 40
10
1.3
DN 50
17
1.4
DN 65
Wärtsilä 34DF Product Guide - a16 - 23 September 2016
9-11
9. Cooling Water System
Wärtsilä 34DF Product Guide
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