Operation as a Gage Pressure Manometer

TM 9-6685-202-14, C1

Altitude

Pressure

Altitude

Pressure

Altitude

Pressure

(feet)

in. Hg

mm Hg

(feet)

in. Hg

mm Hg

(feet)

in. Hg

mm Hg

70400

1.28567

32.656

73800

1.09345

27.774

77000

0.939529

23.864

70600

1.27345

32.346

74000

1.08311

27.511

77200

0.930682

23.639

70800

1.26135

32.038

74200

1.07287

27.251

77400

0.921922

23.417

71000

1.24938

31.734

74400

1.06273

26.993

77600

0.913248

23.196

71200

1.23751

31.433

74600

1.05269

26.738

77800

0.904656

22.978

71400

1.22577

31.135

74800

1.04274

26.486

78000

0.896148

22.762

71600

1.21414

30.839

75000

1.03290

26.236

78200

0.887722

22.548

71800

1.20262

30.547

75200

1.02314

25.988

78400

0.879377

22.336

72000

1 19122

30.257

75400

1.01349

25.743

78600

0.871114

22.126

72200

1.17992

29.970

75600

1.00392

25.500

78800

0.862931

21.918

72400

1.16874

29.686

75800

0.994453

25.259

79000

0.854826

21.713

72600

1.15767

29.405

76000

0.985074

25.021

79200

0.846799

21.509

72800

1.14670

29.126

76200

0.975787

24.785

79400

0.838851

21.307

73000

1.13584

28.850

76400

0.966589

24.551

79600

0.830979

21.107

73200

1.12509

28.577

76600

0.957481

24.320

79800

0.823183

20.909

73400

1.11444

28.307

76800

0.948461

24.091

80000

0.815462

20.713

73600

1.10389

28.039

NOTE

(1) Prepare the modified barometer in

The mercury which is normally

accordance with paragraph 3-5 b.

above the tube seal valve Is now in

(2) Connect the barometer into the pneumatic

the system and causes the barometer

system (fig. 3-8).

to read 0.1 mm high. Therefore, 0.1

(3) Energize the vacuum pump and evacuate

mm should be subtracted from all

the barometer tube to 20 millitorrs (microns).

readings.

(4) Open the vacuum valve (fig. 3-8) slightly.

(4) For extended use as a manometer, it may

Operate the vacuum valve and relief valve (fig. 3-8) to

be desirable to remove approximately 1/2 cc of mercury

obtain the desired indication on the altimeter.

from the cistern to eliminate the correction noted above.

(5) Compute

the

barometer

pressure

Follow the procedure described in paragraph 4-5a,

indication in accordance with paragraph 3-12b and

adjusting the mercury level so that the barometer reads

obtain the equivalent altitude from table 3-2.

zero.

3-14. Operation as a Gage Pressure Manometer

b. Type A-1 Modified. The maximum absolute

a. Type A-1. The maximum pressure which can

pressure which can be measured using the modified

be measured using the barometer as a gage pressure

barometer is 790 mm of mercury or 15.277 psi. Gage

manometer is 790 mm of mercury or 15.276 psi.

pressures up to 15 psi can also be measured.

(1) Open the tube seal valve at the top of

(1) Prepare the modified barometer in

barometer and leave it open.

accordance with paragraph 3-5b.

(2) Level the instrument and adjust the

(2) Open the tube evacuation line and valve

temperature correction if necessary.

to vent the tube to atmosphere.

(3) Apply the pneumatic pressure to be

measured to the cistern by means of 1/4-inch rubber

measured to the cistern nipple (fig. 3-8).

tube connected to the cistern nipple (fig. 1-2).

(4) Compute the pressure indication in

accordance with paragraph 3-12b.

3-15.

Operation as a Differential Pressure

Manometer

a. Type A-1

3-20