The pressure of an absolute vacuum pump, according to the definition, refers to the absolute pressure it generates.
Understanding Absolute Pressure in Vacuum Technology
The concept of pressure in the context of vacuum pumps is measured in terms of absolute pressure. This is the real vacuum pressure achieved by the pump. The goal of a vacuum pump is to reduce this absolute pressure as much as possible.
The provided reference defines the relationship between different pressure measurements:
$$
\text{Absolute pressure} = \text{local atmospheric pressure} + \text{surface pressure (relative pressure)}
$$
Here's a breakdown of these terms:
| Term | Description |
|---|---|
| Absolute Pressure | The actual pressure relative to a perfect vacuum (zero pressure). |
| Local Atmospheric Pressure | The pressure exerted by the Earth's atmosphere at a specific location. |
| Surface Pressure (Relative Pressure) | The pressure measured relative to the local atmospheric pressure (often called gauge pressure). |
The reference states that the smaller the absolute pressure is, the closer to vacuum! Achieving a perfect or "absolute vacuum" (zero absolute pressure) is an theoretical ideal; real-world vacuum pumps can only achieve very low absolute pressures, approaching this ideal.
How Vacuum Pumps Work
Vacuum pumps function by removing gas molecules from a confined volume, thereby lowering the absolute pressure within that volume. Different types of vacuum pumps are designed to operate in various pressure ranges, from rough vacuum (pressures just below atmospheric) to high and ultra-high vacuum (extremely low pressures).
- Rough Vacuum Pumps: Reduce pressure from atmospheric down to typically a few Torr or mbar.
- High Vacuum Pumps: Operate in the range of $10^{-3}$ to $10^{-7}$ Torr or mbar.
- Ultra-High Vacuum Pumps: Achieve pressures below $10^{-7}$ Torr or mbar, often down to $10^{-12}$ Torr.
The term "absolute vacuum pump" might imply a pump capable of achieving very low absolute pressures, close to a theoretical perfect vacuum. The pressure achieved by such a pump would be a very small positive value of absolute pressure.
In summary, the pressure of an absolute vacuum pump is its absolute pressure, which represents the true pressure level above a theoretical perfect vacuum. The lower this absolute pressure, the more effective the pump is at creating a vacuum.
