Volvo Penta SX-A Operator's Manual page 146

Maintenance
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50641
Pitot Tube (Speedometer Port)
The pitot tube, located at the leading edge of the lower
unit, provides pressure input for the speedometer. If
the pitot tube becomes clogged (e.g. the boat runs
aground or the sterndrive drags through silt as the boat
is loaded onto the trailer), the speedometer may stop
functioning. There are two methods for clearing debris
from the pitot tube:
Method 1
Use a six inch length of stiff wire of 1/8 in. (3 mm)
thickness or a wire coat hanger to push any debris in
the pitot tube into the drive cavity.
Method 2
Use compressed air to clear the pitot tube.
1. The pitot tube hose A is attached to the shift cable
hose located inside the transom shield, just
behind the engine. Once you have located the
pitot tube hose, remove the speedometer
hose C from the plastic barb fitting B.
2. Attach the hose from an air compressor to the
barb fitting.
3. Have someone assist you by placing a rag in front
of the pitot tube at the leading edge of the lower
unit.
4. Blow air, pressurized to no more than
116 PSI (800 kPa), into the pitot tube hose until
your assistant can feel the air exiting the pitot
tube.
CAUTION!
Do not place bare hand(s) in front of the pitot tube
to check for air flow as debris may be ejected
forcefully enough to cause an injury.
NOTICE! Do not exceed 116 PSI (800 kPa) as
this may damage the drive.
5. Reattach the speedometer hose to the barb fitting
on the pitot tube hose.
47701898 12-2010