Chemglass AF-0349 Welch Vacuum Pump User Manual
Page 8
8
Section 2: PUMP FEATURES AND PRINCIPLES OF OPERATION
2.01
General Description
All of the Welch Vacuum Pumps are two-stage, rotary-vane, oil sealed vacuum pumps.
These Vacuum Pumps offer a number of features that improve performance, or protect the pump or vacuum system
under specific operating conditions.
2.02
Principles of Vacuum Pump Operation
The main purpose of a vacuum pump is to reduce the pressure in a vessel or a closed system. The degree of pressure
reduction is dependent upon the requirements of the application and the type of vacuum pump employed. Rotary
vane, oil-sealed vacuum pump operation is described in this section.
Pressure reduction in a closed system is accomplished by repeatedly removing a portion of the original volume of gas
contained in the system. Removal is performed by the action of the rotating elements of the pump which cause a
given space to be successfully enlarged and diminished. Figure 2.1 illustrates a section through a typical stage of
rotary-vane pump. Note that this figure is not intended to illustrate exactly the internal components of the pumps; its
purpose is to illustrate the general operating principles of vacuum pumps.
The rotary action of the pump creates a hollow space of chamber (1) which expands as the pump rotates. As the
chamber expands, the pressure in the chamber decreases. As a result, gas is drawn into the chamber due to the
difference in pressure between the chamber and the inlet (4) to the chamber. (The inlet is the only place where gas
can flow into the chamber.) Once the vane (3) moves past the inlet (4), it seals the inlet against the chamber (1) and
the gas becomes trapped between the vanes (2 and 3). The chamber (1) formed by the enclosed space between the
vanes then begins to decrease in volume as the rotor revolves, compressing the gas. The pressure of the compressed
gas becomes greater than atmospheric pressure. When the vane (2) moves past the exhaust port (5) the compressed
gas in the chamber is forced out through the exhaust port.
Figure 2.1
Typical Rotary Vane
Pump, Schematic Diagram
This expansion/compression cycle constitutes one complete cycle of the pump operation. This cycle is repeated as
the vane (2) passes the intake port and seals it against the atmosphere. Therefore, two pump cycles are per-
formed during each revolution of the pump rotor.