Pump

1 . A pump comprising:

a pumping unit including therein an impeller for sucking and discharging a liquid; and

a pump case accommodating therein the pumping unit and provided with an inlet for sucking the liquid into the pump and an outlet for discharging the liquid out of the pump,

wherein the impeller has an inlet mouth portion of a cylindrical shape that projects towards the pump case, and the pump case has a case inlet portion and an annular recess portion which the inlet mouth portion of the impeller is movably inserted in and is formed at the vicinity of the case inlet portion.

2 . The pump of claim 1 , wherein a protrusion is formed at a front shroud part of the impeller, and a recess in which the protrusion is movably inserted is formed at a casing wall surface of the pump case.

3 . The pump of claim 1 , wherein a rib is formed at an outer peripheral wall surface of the inlet mouth portion of the impeller, and a depression in which the rib is movably inserted is formed at an inner peripheral wall surface of the annular recess portion.

4 . The pump of claim 1 , wherein V-shaped grooves are formed at an outer peripheral wall surface of the inlet mouth portion of the impeller.

5 . The pump of claim 1 , wherein the inlet mouth portion of the impeller is configured by a magnet, and a magnetic fluid is adhered to the magnet by a magnetic force, and

wherein a space between the inlet mouth portion and the annular recess in which the inlet mouth portion is movably inserted is filled up with the magnetic fluid.

6 . The pump of claim 1 , wherein an end portion of the case inlet portion projects up to such a height as not to impede a suction of the liquid into the impeller.

7 . The pump of claim 1 , wherein a slanted surface or a curved surface that slopes in a direction from an inner side of the case inlet portion to an outer side thereof is formed at the end portion of the case inlet portion.