These rotary piston blowers (Roots principle), used in vacuum operation, are distinguished by the letter "G". The subsequent letters "L" or "M" indicate the direction of flow.

The numbers, e.g. "14.9", indicate the model size. The letters "HV" following mean "high vacuum" and the letter "m" following means "with auxiliary inlet". 

The radial sealing rings run on a hardened and ground shaft protection sleeve. The oil chamber ensures that the radial sealing rings are vacuum-tight and have a long service life.

The level of sealing oil can be checked visually through the transparent oil tank. Oil must be always be present. (see: Lubrication)

Concerning the blower types HV 18.17 to 20.21 the sealing ring casings at the driving shaft are to be provided with cooling water. The connections are designed in G 1/4". All other blowers do not need a water cooling.

Externalmachined parts are coated with rust preventing varnish, and the inlet and outlet flanges are fitted with plastic caps to prevent the entry of dirt and water spray.