MIL-HDBK-1164
a)
Mechanically Operated Loss-of-Head Gage. The equipment that
operates the indicator, or indicator recorder instrument, requires the maintenance
operations described in the following paragraphs. The inspector should follow these
instructions in general and consult the manufacturer's instructions for detailed
adjustments.
(1)
Each month, check the zero setting in the following way.
Open the equalizing valve on mercury float-type head gages and make certain that the
indicator arm and the recording pen return to zero. Note the reason for any incorrect
reading, and adjust the stop collar or wire cable, if necessary, to bring the indicator to
the proper zero reading. On floats and float chambers that are so equipped, release
the air. (On some models it is possible to release the air by jerking the wire cable
lightly.)
(2)
Each month, remove the float from the float chamber, wash
the float, and remove encrustations. Use care not to mar the float. Replace the
mercury, if necessary, avoiding any spillage. When replacing the mercury, be sure that
the amount is correct. Also, paint the interior and exterior of the float chamber and
other parts each year to prevent corrosion. In addition, check the pressure pipelines to
the float chamber and remove any encrustation.
Caution: Mercury fumes are poisonous. Handle mercury carefully since a
spill creates a continuing health hazard and is difficult to clean up.
b)
Diaphragm-Pendulum Unit Loss-of-Head Gage. When the
actuating mechanism is of this type, the following general maintenance procedures
apply. For a more detailed discussion of the procedures, consult the manufacturer's
instruction.
(1)
Each month, purge the diaphragm cases of air and check
the cable to be sure that it leaves the segment at a tangent to the lower end when the
unit reads zero. Remove dirt from the knife edges; if necessary, tighten the cam hubs
on their shafts. Drain mud from the mud leg as described in par. 11.5.5.8(a)(2) above.
(2)
Check the pipelines to the diaphragm twice a year to make
sure that they are open and free of encrustation.
(3)
Inspect the diaphragms each year for leakage. Replace if
necessary.
Note: Spare diaphragms should be kept underwater.
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