Operation as a Vacuum Manometer

TM 9-6685-202-14

(1) Open the tube seal valve and leave it

(1) Open the tube seal valve, and leave it

open.

(2) Level the instrument and adjust the

(2) Level the barometer and adjust the

temperature correction, if necessary.

temperature correction if necessary.

(3) Connect the low pressure side of the

(3) Connect the vacuum source to be

system to be measured to the tube-evacuation nipple

measured to the tube evacuation nipple (fig. 1-2).

(fig. 1-2).

(4) Subtract 0.1 mm from the reading to

(4) Connect the high pressure side of the

compensate for the additional mercury as noted in

system to be measured to the cistern nipple.

paragraph 3-14.

(5) Open appropriate valves to apply

b. Type A-1 Modified

pressures.

(1) Prepare the modified barometer in

(6) Subtract 0.1 mm from the reading to

accordance with paragraph 3-5b.

compensate for the additional mercury as noted in

(2) Connect the vacuum source to be

paragraph 3-14.

measured to the barometer tube evacuation connection.

b. Type A-1 Modified.

Differential pressures

(3) Compute the vacuum indication in

between 0 and 790 millimeters of mercury

accordance with paragraph 3-12 b.

(approximately 15 psi) can be measured with the

3-17.

Operation as an Absolute Pressure

modified barometer.

Manometer

(1) Prepare the modified barometer in

a. Type A-1. Using the instrument as an absolute

accordance with paragraph 3-5b.

pressure manometer is identical to using it as a

(2) Connect the low pressure side of the

barometer, except that the pressure to be measured

system to be measured to the barometer tube

rather than atmospheric pressure is applied to the

evacuation connection.

cistern. Refer to paragraph 3-12a for operation as a

barometer.

(3) Connect high pressure side of the system

to be measured to the cistern nipple.

b. Type A-1 Modified. Using the instrument as an

absolute pressure manometer is identical to using it as a

(4) Open the appropriate valves to apply

barometer, except that the pressure to be measured

pressures.

rather than atmospheric pressure is applied to the

(5) Compute

the

differential

pressure

cistern. Refer to paragraph 3-12b for operation as a

indication in accordance with paragraph 3-12b.

barometer.

3-16. Operation as a Vacuum Manometer

a. Type A-1

3-21