1.2.7 pV throughput
Dividing the general gas equation (Formula 1-6) by time t obtains the gas flow
\[q_{pV}=\frac{p\cdot V}t = \frac{m\cdot R\cdot T}{M\cdot t}\]
Formula 1-15: pV throughput
| $q_{pV}$ | pV throughput | [Pa m3 s-1] |
As can be seen from the right-hand side of the equation, a constant mass flow is displaced at constant temperature T. This is also referred to as pV flow or gas throughput. Throughput is the gas flow rate transported by a vacuum pump.
\[q_{pV} = S\cdot p = \frac{dV}{dt}\cdot p\]
Formula 1-16: Throughput of a vacuum pump
Dividing the throughput by the inlet pressure obtains a volume flow rate, the pumping speed of a vacuum pump:
\[S = \frac{dV}{dt}\]
Formula 1-17: Volume flow rate, or pumping speed, of a vacuum pump
A conversion table for various units of throughput is given in Table 1.8.
| Pa m3 / s = W | mbar l / s | Torr l / s | atm cm3 / s | lusec | sccm | slm | Mol / s | |
|---|---|---|---|---|---|---|---|---|
| Pa m3 / s | 1 | 10 | 7.5 | 9.87 | 7.5·103 | 592 | 0.592 | 4.41·10-4 |
| mbar l / s | 0.1 | 1 | 0.75 | 0.987 | 750 | 59.2 | 5.92·10-2 | 4.41·10-5 |
| Torr l / s | 0.133 | 1.33 | 1 | 1.32 | 1,000 | 78.9 | 7.89·10-2 | 5.85·10-5 |
| atm cm3 / s | 0.101 | 1.01 | 0.76 | 1 | 760 | 59.8 | 5.98·10-2 | 4.45·10-5 |
| lusec | 1.33·10-4 | 1.33·10-3 | 10-3 | 1.32·10-3 | 1 | 7.89·10-2 | 7.89·10-5 | 5.86·10-8 |
| sccm | 1.69·10-3 | 1.69·10-2 | 1.27·10-2 | 1.67·10-2 | 12.7 | 1 | 10-3 | 7.45·10-7 |
| slm | 1.69 | 16.9 | 12.7 | 16.7 | 1.27·104 | 1,000 | 1 | 7.45·10-4 |
| Mol / s | 2.27·103 | 2.27·104 | 1.7·104 | 2.24·104 | 1.7·107 | 1.34·106 | 1.34·103 | 1 |
Table 1.8: Conversion table for units of throughput
