(19)
(11) EP 0 381 413 A3

(12) EUROPEAN PATENT APPLICATION

(88) Date of publication A3:
05.12.1990 Bulletin 1990/49

(43) Date of publication A2:
08.08.1990 Bulletin 1990/32

(21) Application number: 90300894.4

(22) Date of filing: 29.01.1990
(51) International Patent Classification (IPC)5: F04C 2/107, F04C 5/00
(84) Designated Contracting States:
AT BE CH DE DK ES FR GR IT LI LU NL SE

(30) Priority: 01.02.1989 GB 8902230

(71) Applicant: MONO PUMPS LIMITED
Audenshaw, Manchester M34 5DQ (GB)

(72) Inventors:
  • Mathewson, Lindsay Thomas
    Buxton, Derbyshire (GB)
  • May, Geoffrey Harold
    Rochdale, Lancashire OL11 4DN (GB)

(74) Representative: Allen, William Guy Fairfax et al
J.A. KEMP & CO. 14 South Square Gray's Inn
London WC1R 5LX
London WC1R 5LX (GB)


(56) References cited: : 
   
       


    (54) Helical gear pump


    (57) A helical gear pump is described in which the geometry of the stator (8) and rotor (22) are modified such that the interference is significantly more at the locations of the minor diameter d than the locations of the major diameter D of the rotor. The rotor (22) is preferably plasma coated with modified chromium oxide and the base metal of the rotor is advantageously machined so that in the region of locations of major diameter D, the thickness of the plasma coating (28) is less and, in the region of the locations of minor diameter d, the thickness of the plasma coating (28) is greater than in the remainder of the rotor (22) while allowing the interference to be significantly more at the locations of the minor diameter d than at the locations of the major diameter D.







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