Suction device, especially for use in dentistry

A suction device, especially for use in dentistry, having three series connected compressor stages comprising

• (a) a shaft (26) connectable to an electric motor (28);
• (b) a rotor (24) mounted on said shaft (26), which rotor is formed with two parallel end faces, each of which is provided with side-channel compressor vanes (38, 42) adjacent to the periphery of the rotor;
• (c) a casing (12, 16) defining a disc shaped rotor chamber having parallel end faces cooperating with the rotor (24) in essentially fluid tight manner to form first and second side-channels (44, 52) with the end faces of the rotor chamber, each side channel having an intake section and an outlet section;
• (d) an axial connecting channel (48) connecting the outlet section of the first side-channel to the inlet section of the second side-channel, the outlet section of the second side-channel being connected to an outlet orifice (62) of the casing (12, 16), while the intake section of the first side-channel (36) communicates with an inlet orifice (70) of the casing (12, 16);
• (e) the rotor (24) having a central hub portion (68) that surrounds said shaft (26), guide wall (66) annularly spaced from the hub portion and radially flaring towards said first side-channel (36) so as to form an axial passageway extending completely through the rotor (24), compressor vanes (64) mounted entirely within the annular space extending between the hub portion (68) and said guide wall (66);
• and
• (f) a first end face of said casing (12) being formed with an intermediate channel (78) that is aligned with an opposing end portion of the guide wall (66) and having a radially outwardly extending connection section (80) communicating with the first side-channel (36).