You also want an ePaper? Increase the reach of your titles
YUMPU automatically turns print PDFs into web optimized ePapers that Google loves.
Pfeiffer <strong>Vacuum</strong><br />
Formula 1-11<br />
pV flow<br />
Formula 1-12<br />
Definition of volume flow<br />
rate, or pumping speed<br />
Formula 1-13<br />
<strong>Vacuum</strong> pump throughput<br />
Page 16<br />
<strong>Vacuum</strong> <strong>Technology</strong><br />
Pipe diameter d<br />
100<br />
cm<br />
10<br />
1.2.7 pV flow<br />
Transitional Area<br />
1<br />
10 -5 10 -4 10 -3 10 -2 10 -1 10 0 10 1 10 2 10 3<br />
Molecular<br />
Figure 1.6: Flow ranges in vacuum<br />
Dividing the general gas equation by time t yields the gas flow<br />
p . V m . R . T<br />
q pV = =<br />
t t . M<br />
This is also referred to as pV flow. As can be seen from the right-hand side of the equation, a<br />
constant mass flow is displaced at constant temperature T.<br />
<strong>Vacuum</strong> pumps, particularly positive displacement pumps, have a constant volume flow rate of<br />
S =<br />
over a given inlet pressure range; i.e. they displace a constant volume flow. Multiplying the<br />
volume flow rate by the inlet pressure yields the throughput of a pump<br />
Throughput is the gas flow transported by a vacuum pump.<br />
dV<br />
dt<br />
dV<br />
q pV = S . p = . p<br />
dt<br />
viscous<br />
Pressure p<br />
mbar<br />
www.pfeiffer-vacuum.net
Change language