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|  MIL-T-21578A
Throttling - All pressure gages shall be equipped with
3.4.4.7.3
needle valves located as close as practicable to the gage.
Protection - Gages subject to pressure beyond their maxi-
3.4.4.7.4
mum range shall be protected with automatic gage shut-off valves. Automatic
gage shut-off valves shall be of positive action which will allow no leakage of fluid
to the gage. A suitable in-line filter shall be provided in the circuit immediately
ahead of the shut-off valve. The differential between the cut-off and cut-on point
percent of the range of the gage,
shall not exceed
Calibration taps - A calibration tap shall be included be-
3.4.4.7.5
tween each gage and the throttling valve to facilitate the calibration of the pressure
gage from the front of the test equipment.
Air bleed (pressure gages] - Where maximum accuracy
3.4.4.7.6
is required in low pressure gages and where the fluid head in the lines will cause
a significant error in the gage reading, provisions shall be made to purge gage
lines of air and maintain a constant liquid head on the gage.
Drip indicator - Bleed lines on pressure gages shall be
3.4.4.7.7
provided with visible drip indicators.
Taps - All pressure gages shall be provided with a tap on
3.4.4.7.8
the panel between the gage and the gage shut-off valve to permit calibration of the
gage without removal from the panel.
Measuring section - Where it is necessary to measure inlet
3.4.4.8
or discharge pressure in the lines connected to the accessory, special measuring
sections shall be included with the equipment. Measuring sections shall be pro-
vided only on stands designed for testing fuel controls, fuel nozzles, and fuel regu-
lators.
Design of measuring sections - Each section shall consist
3.4.4.8.1
of a length of straight stainless steel tubing with an inside diameter the same as
the standard fitting installed in the accessory pressure tap. A gage connection
shall be installed in this tubing preceded by 5 diameters length of tubing and
followed by 5 diameters length of tubing. The tubing and connection shall be free
of any restrictions which could affect the accuracy of the indicated pressure.
Couplings - Quick-connect couplings providing unrestricted
3.4.4.8.2
streamlined flow shall be used between the measuring section and the accessory.
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