Screw vacuum pump with bypass valve has through aperture of such dimensions that valve closing piece does not contact valve seat during beginning of evacuating phase

摘要

The pump has a dipping cavity casing (1) containing two rotors with external thread starts, and a bypass valve to prevent excessive pressure in the casing. This valve has a through aperture (2) in the casing wall, and a closing piece (3) for this aperture outside the cavity. This cavity is of such dimensions that valve closing piece does not contact valve seat during beginning of evacuating phase