Section II - General Description
• What is vacuum and how is flow rate understood
• Introduction
• Flow diagram
• Condensate system
• Regulating system
• Electrical System
What is vacuum and how is flow rate understood
What is vacuum and how to denote
A vacuum is any pressure in a system that is below the ambient atmospheric pressure. It
can be denoted in absolute terms or in effective (gauge) terms:
•
mbar(a) - absolute pressure - denotes how much the pressure is above absolute zero
vacuum.
• (minus) mbar(e) - the effective or gauge pressure - denotes how much the pressure is
below local atmospheric pressure.
(1)
Pressure
(2)
Absolute vacuum
(3)
Typical QSV pump working range (400 mbar(a) – 10 mbar(a))
(4)
Atmospheric pressure
Atmospheric pressure at sea level is roughly 1 bar or 1000 mbar. A typical working range
for the QSV pumps is 400 mbar(a) to 10 mbar(a). From the illustration it can be seen
clearly that this range is also equivalent to -600 mbar(e) and -990 mbar(e).
It is important to understand which type of reference is required before selecting a
pressure instrument for measuring the vacuum. It must be noted that the distinction
doesn’t matter for a pressure difference (delta P; e.g. pressure loss), since it is always the
result of subtracting 2 pressures (whether stated as absolute or effective pressures).
Flow rate definitions
There are 2 common but different ways to denote flow rate in vacuum. The first one is
based on the displacement or volumetric flow rate and the second one is based on the
throughput or mass flow rate. Quincy vacuum pumps use volumetric flow rate to denote
performance, the unit being Acfm.
8
Quincy Vacuum Pump-QSV Series
