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380602.01
vetus®
Installation manual Generator Sets GHX / GLX
3.4.4 Prevention of siphoning
Another means of water intrusion is through the raw water intake sea-cock. This can occur when the raw water injection
point at the exhaust elbow is below the worst case water level.
What happens is that, upon engine shut-down, raw water siphons from the intake sea-cock, up through the raw water
cooling circuit containing the raw water pump, heat exchanger, and water injected exhaust elbow, into the water lift
muffler.
This raw water will siphon past the impeller of the sea water pump and fill the muffler and all hoses attached to the muf-
fler until the outside water level is reached. If the engine exhaust manifold is below the worst-case water level, raw water
will simply pour into the cylinders, destroying the engine.
This form of water intrusion is avoided by the proper installation of an air vent (anti-siphon) in the raw water circuit
between the heat exchanger outlet and the water injected exhaust elbow inlet. The air vent must be well above the
worst case water level under all conceivable conditions of boat trim, boat operation, sea conditions, and heel angle. The
anti-siphon break and the exhaust hose point should be located as near to the boats centre-line as possible; especially on
sail-boats due to large and steady healing. The anti-siphon must be accessible for maintenance.
The valve of an air vent is closed during normal operation of the engine; during a standstill of the engine the water pres-
sure in the raw water line drops and the valve will open to let air in to break the water column.
3.4.5 Air vent installation
Remove the connection hose (1) from the heat
exchanger to raw water inlet at the exhaust
elbow.
Remove the blind plugs (2) out of the wall of
the sound box.
Feed the hoses through the released holes. Fit
the air vent (3) at a height of minimal 40 cm
(16”) but not more than 2 metres (3’ 8”) above
the water line. In a sail-boat the air vent must
also be positioned as far as possible midships.
This prevents the air vent from being less than
the required 40 cm (16”) above the waterline
when the ship is sailing is heeling. These hoses
must be installed in a sloped position.
If an air vent without a valve is installed a vent
hose of 8 mm diam. (5/8”) must be installed.
When the engine is running a small amount
of water will escape, but as soon as the engine
stops air will enter the water hose and break
the siphoning ability of the system thus
preventing the water from penetrating the
exhaust.
1
2
MIN. 40 cm (16”)
WL
3
