Toro 51643 Service Manual page 35

Fuel Cap Operation (cont'd)
When a vacuum occurs within the tank, the following
occurs: See Figure 48.
UMBRELLA VALVE
Figure 48
1. Atmospheric pressure enters the top of the gas cap
through the slits
in
the gas cap threads.
2. Because a vacuum in the tank means that higher
pressure is present outside the tank than within,
the higher pressure passes down the stem of the
umbrella valve and forces the stem orifice open.
3.
The higher pressure passes through the packing
orifice and enters the fuel tank thereby equalizing
the pressure.
Fuel Cap Disassembly
1. Remove the fuel cap from the tank.
2.
Pry the gasket, holder and breather valve out of the
tank cap. See Figure 49.
Fuel Cap Inspection
1.
It is important that the fuel cap properly vents the
tank. Inspect the gasket to ensure that the hole at
the rounded end is unobstructed.
2. Check the
two
small pressure outlet holes in the
holder to ensure that they are open.
3.
The stem of the umbrella valve allows air into the
tank to compensate for the fuel being used by the
engine. Ensure that
it
will open and close by
holding the flat end lengthwise between your
thumbs and squeezing. See Figure 50.
4.
Clean all fuel cap parts thoroughly.
Fuel Cap Reassembly
1.
Position the holder inside the gasket, then screw
this assembly into the fuel cap until
it
is fully seated
in the top of the fuel cap.
2 .
Reinstall the cap on the fuel tank.
Figure 49
3. Clean these parts thoroughly.