Installation Manual
N38143 Chapter 2
Page 5
Syphon break
A syphon break admits air to the top of any ‘inverted U bend and prevents unwanted syphonic action.
The syphon break should vent through a skin tting well above the water level.
Some commercially available syphon break units contain a valve to prevent water loss through the vent pipe
and vent within the vessel.
Note: Syphon breaks with a valve requires periodic maintenance, checks should be carried out every time the
engine oil is changed.
Caution: Do not overcrank your engine when it will not start or crank the engine to bleed the fuel system, as
there will not be the exhaust gas present to empty the exhaust riser. Water lls the riser and can back up the
exhaust and ll the engine. The seacock must be closed and raw water pump impeller removed if the engine
is to be cranked for more than one minute. Remember to replace the impeller and open the seacock when
nished.
Top of the exhaust riser and the point at which the syphon break (C1) is connected to the engine pipework must
be above the water line (C6) under the worst possible conditions (normally a distance of 450mm (18 inches)
(C2) under static conditions will be sufcient). There should be a minimum distance of 300mm (12 inches) (C3)
between the exhaust tank inlet (C4)and the water injection elbow (C5).
Note: Minimum volume of exhaust mufer/water lift should be three times the volume of the water in the riser.
The tank should be installed near the centre-line of sailing craft.
Warning! Sea water inlet ttings with a scoop must not be used. The pressure generated when the vessel is
under way can force the water past the raw water pump when the generator is not in operation, thus allowing
water to ll up the water lift. With no exhaust pressure to force the water out of the system, water can enter the
engine via the exhaust manifold.