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Connections to the silencer should be made using suitable exhaust hose, which is type
approved by Lloyds and DNV. Do not use oil or grease to lubricate hoses when installing,
wetting the inside of the hoses with water will help them slip more easily over the silencer
spigots. A minimum of 2 hose clips must be used. Securely tighten all hose clamps, but be
careful not to overtighten.
The silencer should be positioned within 300mm of the centre line of the vessel, or to the
engine on which it is installed. This is particularly important on sailing vessels where a
substantial angle of heel can be encountered. On systems where the exhaust manifold is
near or below the water line. A siphon break should be used to prevent the water flow
continuing after the engine shut down.
In all installations the silencer should be at the lowest point if the entire exhaust system. The
top of the silencer should be at least below the exhaust manifold outlet for the best
performance. If a distance less than is allowed, the margin of safety for preventing reverse
flow of water toward the manifold will decrease.
• Siphon Breaker Fitting Instructions
1. The unit must be positioned upright, well above waterline. The height above
waterline will vary from vessel to vessel but will be between 150mm and 2 metres.
Please seek guidance on this if you are unsure, or if you are not familiar with the
correct way to incorporate a siphon breaker into your particular exhaust system.
2. The inverted "U" bend at the top must be connected to a hose draining into the
bilge, or over the side of the vessel. In no circumstances must this drain into a
sealed container, such as a bottle due to the risk of back siphoning. After fitting,
run the engine and check the unions for leaks. Check again after 5 running hours.
3. The siphon break is equally suitable for use with a marine toilet water inlet.
4. The ½" unit may also be used with 5/8" systems. The 3/4" and 1" units may only
be used with the correct hose.
• Siphon Breaker Maintenance
1. On commercial vessels achieving in excess of 150 engine hours per year, the unit
should have the small valve removed from the top and this should be thoroughly
washed in warm soapy water to remove salt encrustation.
2. On a pleasure vessel this should be done twice a year.
3. On reassembly the engine should be run and the unit checked for leaks. The hose
junctions should also be checked for leaks as part of the daily inspection procedure
for sea cocks, water pipes, oil levels, etc.
RDG603A81 – Issue 2
Page 34 of 93
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