Operation of Constant Vacuum Regulator

TM 9-6685-202-14

To completely remove all oil, invert the pump and turn

(9) Rubber tubing connections should be kept

the shaft several revolutions to flush out any remaining

as short as possible and made with an extra heavy wall,

oil.

gum tubing, which has been compounded specially for

vacuum work. All connections to metal or glass tubing

CAUTION

should fit snugly and both members should be coated

with vacuum stopcock grease.

Tygon tubing is

adequate for most applications.

Do not use solvents or light flushing

oils.

Their complete removal is

(10) Metal vacuum valves and glass stopcocks

difficult and their high vapor

are employed generally in the connecting line between

pressures will prevent the attainment

the pump and the system to provide a means of

of a high vacuum.

connecting the vacuum gage and for vacuum release

when stopping the pumping.

(4) If the oil has thickened or contains sludge,

it is advisable to remove the oil reservoir case and

CAUTION

thoroughly clean the case with lint-free rags. Varnish a

new gasket and install it on the case. Tighten all screws

Take care to prevent solid particles

uniformly. Also replace the shaft seal.

from reaching the pump intake.

Particles can score the working parts

(5) The frequency of oil change depends

of the pump and reduce its

upon the service or use of the pump. If the pump is

efficiency. If corrosive vapors or

operating against a vaporless dustless system, change

large amounts of water vapor are in

oil once every six months; if vapors pass through the

the system, use a freezing trap in the

pump in any quantity, a daily change of oil may be

needed.

line to prevent them from entering

the pump and to keep pump oil

(6) During shipment, the intake nipple of the

vapor from entering the system. Use

vacuum pump is closed to prevent entrance of foreign

a mixture of dry ice and acetone or

matter into the pump. In handling the pump, similar

ethyl alcohol as a vacuum flask

precautions should be exercised. In connecting the

refrigerant.

pump to the system to be evacuated, extreme care must

be taken to eliminate leakage. All connections should

3-8. Operation of Constant Vacuum Regulator 6685-

be as short as possible, and of large diameter. When

306-5604

the pump is operating in the low micron range, the flow

of gas through a tube is substantially molecular in

a. The constant vacuum regulator is a hand set

character. At low pressures, the gas removed from the

device which maintains set pressures within close limits

system is confined largely to those molecules which

over extended periods. The regulator is suitable for

because of their kinetic energy of agitation, happen to

both vacuum and pressure systems for calibrating and

hit the intake of the pump when the cylinder of the pump

testing pressure sensitive instruments and for controlling

is open to the intake.

vacuum apparatus.

The regulator is continuously

(7) If metal piping is used, it is the best

adjustable over the entire range by a handwheel. No

practice to solder or braze all connections. When

external reference pressure is required.

threaded pipe joints must be used, the threads should

be as nearly perfect as possible. In such a connection,

KEY to fig. 3-3.

screw the members together several turns, and then

Adjusting handwheel

apply black glyptal to the exposed threads before

Control spring

screwing together tightly. Allow the glyptal to dry

Spring and bellows connector

several hours before starting the pump. If flanged

Vacuum throttling value

connections are used, flat or o-ring gaskets made of

Vacuum pump connection

rubber or neoprene should be used between the parts to

Test connection

reduce leakage. Place a thin coat of vacuum stopcock

Bellows

grease on the o-ring before using.

Air inlet

Air filter

(8) When standard tapered or ball and TM 9-

10.

Valve port

6685-202-14 socket joints are used in connections, a

11.

Valve disc

vacuum stopcock grease should be used on both

12.

Adjusting screw

members.

3-7