Yanmar 4LHA-DTP, Operation Manual

Page: 529 / 670

Chapter 6 Cooling Water System
5. Pressure Cap and Sub Tank
, 4LHA Series
5. Pressure Cap and Sub Tank
5-1 Pressure cap construction
The pressure cap mounted on the fresh water filler neck
incorporates a pressure control valve. The cap is mounted
on the filler neck cam by placing it on the rocking tab and
rotating. The top seal of the cap seals the top of the filler
neck, and the pressure valve seals the lock seat.
5-2 Pressure cap pressure controi
The pressure valve and vacuum seal both seal the valve
seat when the pressure in the fresh water system is within
the specified value of 0.088(0.9)MPa(kgf/cm). This seals
the fresh water system.
When the pressure within the fresh water system exceeds
the specified value, the pressure valve opens, and steam
is discharged through the overflow pipe. When the fresh
water is cooled and the pressure within the fresh water
system drops below the normal value, atmospheric
pressure opens the vacuum valve, and air is drawn in
through the overflow pipe.
Pressure valve operation
Pressure valve spring
Overflow tube
Pressure valve
Rubber seal
5-3 Pressure cap inspection
Precautions
Do not open the pressure cap while the engine is running
or right after stopping because high temperature steam
will be blown out. Remove the cap only after the water has
had a chance to cool down.
(1) Remove scale and rust, check the seat and seat valve,
etc. for scratches or wear, and the spring for corrosion
or settling. Replace if necessary.
NOTE: Clean the pressure cap with fresh water as it will
not close completely if it is dirty.
(2) Fit the adapter on the tester to the pressure cap. Pump
until the pressure gauge is within the specified
pressure range [0.0735-0.103(0.75-1.05) MPa(kgf/cm)]
and note the gauge reading. The cap is normal if the
pressure holds for six seconds. If the pressure does
not rise, or drops immediately, inspect the cap and
repair or replace as necessary.
Parts No. of cap tester
120445-44600
Vacuum valve operation
Vacuum valve spring
Vacuum valve
The sub tank, (which will be described later), keeps the
water level from dropping due to discharge of steam when
the pressure valve opens.
Action of pressure control valve
Pressure valve
Open at 0.088(0.9)MPa(kgf/cm
!
)
V a c u u m valve
Open at 0.0049(0.05)MPa(kgf/cm
J
) or below
5-4 Function of the sub tank
The pressure valve opens to discharge steam when the
steam pressure in the fresh water tank exceeds 0.088(0.9)
MPa(kgf/cm).
This consumes water. The sub tank maintains the water
level by preventing this discharge of water.
The steam discharged into the sub tank condenses into
water, and the water level in the sub tank rises.
When the pressure in the fresh water system drops below
the normal value, the water in the sub tank is sucked back
into the fresh water tank to raise the water back to its
original level.
The sub tank facilitates long hours of operation without
water replacement and eliminates the possibility of burns
when the steam is ejected from the filler neck becase the
pressure cap does not need to be removed.
6-12