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8. PERIODIC MAINTENANCE [Minimum Pressure / Check Valve]
8.10
Inspection and Replacement of Minimum Pressure / Check Valve
8.10.1 Adjustment of Minimum
Pressure Valve
Adjustment pressure is preset to 0.44 MPa at the
delivery from the factory.
If some deviation occurs to the control pressure,
readjustment can be done by the following proce-
dures.
q Open the valve at the compressor’s discharge
side. Set the unit to blow operation and check
the pressure by the pressure gauge.
w Remove the cap, fix the adjustment screw by a
hexagon wrench, then unfasten the lock nut.
e Fastening the adjustment screw will increase
the control pressure, and unfastening will de-
crease.
r When a specified pressure is obtained, fix the
adjustment screw again with a lock nut, then
fasten the cap again.
Control pressure adjustment must be car-
ried out while the unit is in operation.
Therefore, ask your dealer or Hitachi ser-
vice station for the work.
CAUTION
8.10.2 Replacement of Minimum
Pressure / Check Valve
q Press the STOP button.
w Turn the power OFF.
e Close the stop valve on discharge side.
r Wait until the pressure in the compressor de-
creases to the ambient air pressure.
t Hook a spanner on a hexagonal portion of the
minimum pressure / check valve body. Do not
unfasten its lock nut portion, remove the body
in whole instead.
y There are a control pressure spring, control
pressure valve body, check valve spring, check
valve body left on the element head side. Take
the part out and replace it with a new one, if
required.
u If there is stain on the sheet surface of the ele-
ment head side, clean it. Spread grease on the
Z-ring portion of the pressure control valve
body, or thinly spread the lubricant (NEW
A OIL 2000) over the piston sliding
portion or sheet surface O-ring portion of the
check valve body, and reassemble them.
i At this time, be careful so that the face side of
the check valve spring (broader surface to its
bottom).
Cap
Adjustment
Screw
Lock Nut
Body
O-ring
Pressure
Control
Spring
Minimum
Pressure
Valve
Z-ring
Check Valve Spring
Check Valve Body
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