Section II. OPERATION UNDER USUAL CONDITIONS

TM 9-6685-202-14

for reading. Tighten set screw.

(g) Check

reading

and

reset

necessary.

(e) Set micrometer to zero reading.

(h) The barometer is now ready for

(f) Loosen shaft set screw and move

operation.

shaft until slight "dimple" can be seen on the mercury

surface. Tighten the set screw.

Section II. OPERATION UNDER USUAL CONDITIONS

from overload. It is recommended

3-6. Controls

that a suitable motor starting switch

with motor overload protection he

a. The barometer contains no controls that must

used for all permanent installations.

be set prior to operation.

The motor is supplied with a

connecting cord and plug for

b. This section describes the procedure for normal

operation on 115 volts.

For

operation of the barometer. It is assumed that the

operation on 230 volts rewire as

instrument is free from maintenance problems as

shown on inside of the cover of the

ascertained in the inspection procedures in paragraph 3-

motor connection box.

2. This section also includes the operation of the

vacuum pump and constant pressure regulator, which

(2) The oil is drained from the pump for

although not part of the barometer, are essential to its

shipment. A gallon of Cenco No. 93050 vacuum pump

operation.

oil is supplied with each pump. Approximately three

quarts are needed in the pump. To fill the pump,

3-7. Operation of Vacuum Pump 4310-2033057 or

remove the top cover and fill with the oil supplied until it

4931-929-8403

is slightly above the oil level as indicated in the window

on one side of the pump. In operation, the oil should be

a. The vacuum pump is a motor-driven, rotary-

even with, or slightly above, the oil level as indicated in

type, oil-sealed pump operating on the principle of the

the window.

eccentric rotor with spring operated moving vanes. Air

at atmospheric pressure is forced into a smaller volume

NOTE

by the action of an eccentric rotor with moving vanes

always in contact, and is expelled from the exhaust port.

The 4931-929-8403 pump is shipped

The pump is a two-stage, series connected type. The

with on quart of Cenco No. 9050

two stages, intake and exhaust, have equal volumetric

vacuum pump oil and is filled

displacement. A single spring actuates each valve. The

through the exhaust port.

entire pump mechanism is immersed in a bath of oil

which insures a tight vacuum seal of the stages, acts as

CAUTION

a coolant, and lubricates the moving parts. The pump

and motor are mounted on a steel base.

Measure the oil carefully.

insufficient oil is used, a good seal

To operate the vacuum pump, proceed

around the vane my not be

as follows: (1) Connect the motor to a power source of

maintained. If too much oil is used,

the voltage, frequency and phase indicated on the

oil my back up through the pump

nameplate of the motor, normally 115 volts, 60 cycles,

trap into the vacuum line.

single phase.

CAUTION

(3) When the oil has become contaminated,

as can be seen through the inspection window, drain the

pump, flush with a small amount of vacuum pump oil

The power line would be heavy

and refill with Cenco vacuum pump oil No. 93050,

enough to carry the current required

Federal Stock Number 9150-273-8663. Most of the oil

without an undue drop in voltage.

may be drained through the drain cock.

Fuses

provide

short

circuit

protection only for the power supply

line and do not protect the motor

3-6