Venturi valve

A venturi valve creates a vacuum with the help of air flow. There is a narrowing in the air duct. As the air flow accelerates when it passes through the narrowing, there is a reduction in pressure in the narrowing (the venturi effect). By means of a side connection in this narrowing, air can be drawn in, thus creating a vacuum.

Advantages
- Very low investment
- Small
- Simple
- Thin hose (compressed air instead of vacuum)

Disadvantages
- Uses compressed air
- Relatively expensive
- Can distribute emulsion as vapour
- No consistent vacuum pressure
- Higher noise level

Oil-lubricated vacuum pumps

A rotor is fitted to the shaft of the vacuum pump. The shaft of the vacuum pump is driven by the motor through a flexible coupling. This rotor is arranged eccentrically in relation to the cylinder, therefore there is a difference in volume on the two sides of the rotor. Vanes slide in grooves in the rotor, such that, combined with an oil film, the chambers are sealed. At the same time, air is drawn in and compressed.

Advantages
- Average/low investment
- High vacuum up to 0.1mbar
- Can run for >24 hours uninterrupted
- Robust and operational reliability
- Long lifetime

Disadvantages
- Cannot withstand leakage (>30%)
- Minimum pressure 300mbar (70% vacuum)
- Oil can be contaminated with moisture

Dry-running rotary vane vacuum pumps

The drying-running rotary vane pumps work on the same principle as the oil-lubricated vacuum pumps, however; These pumps are able to withstand significant leakage. Because there is no oil, there will continue to be a small leakage between the vanes, as a result of which a dry-running pump creates less of a vacuum (85%) than an oil-lubricated vacuum pump (~98%). The vanes are made from graphite as opposed to plastic, because of which these have a self-lubricating action.

Advantages
- Less maintenance
- No risk of oil contamination
- Oil-free

Disadvantages
- Lower vacuum 150mbar (85%)
- Sensitive to moisture
- Shorter lifetime