[0001] The invention concerns a seal device for sealing off between a pump impeller and
an adjacent non-rotating part.
[0002] In pumps with rotating impellers such as centrifugal pumps the pumped medium is sucked
into the centre of the impeller and leaves at the circumference. It is then very important
that the inlet part of the impeller is well fitted within the surrounding pump housing
in order to prevent pumped medium from flowing back to the inlet. Such a back-flow
which is caused by the higher pressure within the pump housing, means losses and creation
of turbulence in the inlet. In addition pollutions may collect between pump impeller
and pump housing inlet.
[0003] In order to obtain the necessary sealing between the impeller and non-rotating parts
it is common practice to arrange a wear part, for instance made of rubber, on the
non-rotating part and let the impeller glide against that part during rotation. In
this way an effective sealing is obtained as long as the wear part is intact. When
pumping liquids containing pollutions such as sand, cloth plastic stripes etc, there
is a risk that the slot between seal ring and pump impeller becomes clogged which
may cause expensive service work. As the pollutions restrain the rotation of the impeller
the energy consumption increases.
[0004] One way to solve the problem is to arrange a mechanical face seal between the impeller
and the housing. By designing the sealing so that the seal slot becomes axially directed
quite a good sealing is obtained. A disadvantage is that this solution is comparatively
expensive and in addition considerable losses may occur.
[0005] Another way to solve the problem is to arrange a co-rotating O-ring on the impeller
inlet part which is influenced by the pressure to glide against the non-rotating surface,
the latter then being made of a different material. A relatively good sealing is obtained
in this way, but on disadvantage is that the wear may be extensive causing short service
intervals. It has also been noted that the O-ring has a tendency to loose its contact.
If this occurs, the self-balancing ends and the seal does not function. This depends
on the fact that dynamic forces caused by the O-ring are co-rotating.
[0006] Still another way to solve the problem is shown in EP-492 603 and US 322 8343 and
322 1661.Here, the pump inlet is so designed that entering leakage flows are linked
in a direction that shall decrease the disturbance of the main in flow.
[0007] According to the invention a secure and wear resistant device is obtained which minimizes
the leakage flow within the pump inlet and which simultaneously decreases the risk
for turbulence within the in flow. The device is described more closely below with
reference to the enclosed drawings where Fig 1 shows a cut through a part of a pump
housing and impeller, while Fig 2 shows an enlarged view of a central part.
[0008] In the drawings 1 stands for a pump impeller having an inlet part 2. 3 stands for
a pump housing with a bottom 4 and a collar formed inlet part 5. 6 stands for a wear
ring, 7 an O-ring and 8 a slot.
[0009] The pumped liquid is sucked in an axial direction into the centrally located opening
of the impeller and leaves the impeller at its circumference. To make it possible
for the impeller to rotate freely, a slot having a certain width must be present between
the impeller and the inlet part of the pump housing. At the same time there is a wish
to make the slot as narrow as possible in order to minimize the back flow from the
inner of the pump housing caused by the higher pressure in the latter.
[0010] According to the invention the inlet part 2 of the impeller I is provided with a
concentric collar which surrounds a similarly collar formed part 5 at the inlet of
the pump housing 3 with a play. The part 5 is than directed opposite the collar 2
and extends somewhat into this.
[0011] The leakage flow that necessarily occurs is then so linked that it enters the main
flow into the impeller almost in parallel, which means that only a minimal disturbance
is caused.
[0012] In order to further diminish the leakage flow and simultaneously decrease the risk
for clogging when pumping polluted liquids, a stationary 0-ring 7 is arranged to cover
the entrance to the slot 8 between the parts 2 and 5. The 0-ring is than attached
to the inner non-rotating part 5.
[0013] It is important that the two parts 2 and 5 extend beyond each other a certain distance
to secure a good result.
[0014] In order to decrease the wear of the inlet 2 within the area of the slot 8, the impeller
is provided with a ring 6 of a wear resistant material on which the O-ring 7 glides.
1. A device to decrease the back flow through the slot between a pump housing inlet and
an impeller, characterized in that the inlet part of the impeller is designed with
an axially directed collar which coaxially surrounds a similarly designed collar formed
opposite part of the pump housing inlet and that the axially directed slot between
the rotating pump impeller inlet and the non-rotating pump housing inlet is sealed
off by a non-rotating 0-ring arranged at the entrance of the slot turned away from
the inner of the pump housing.
