EP0672832A1

EP0672832A1 - Sealing device for pump impeller

Info

Publication number: EP0672832A1
Application number: EP95850055A
Authority: EP
Inventors: Ulf Arbeus
Original assignee: ITT Flygt AB
Current assignee: Xylem Water Solutions AB
Priority date: 1994-03-16
Filing date: 1995-03-13
Publication date: 1995-09-20
Anticipated expiration: 2015-03-13
Also published as: CA2144692A1; DE69502525D1; DE69502525T2; SE9400881L; CA2144692C; EP0672832B1; SE502552C2; JPH08121384A; SE9400881D0

Abstract

The invention concerns a device for sealing off the slot between a pump impeller and a pump housing in a centrifugal pump.

The inlet part (2) of the pump housing (1) is designed with a collar (2) which concentrically surrounds a corresponding opposite collar formed part (5) of the pump impeller inlet, thus linking any possible leakage flow in parallel with the main flow into the impeller and minimizing the disturbance in the main flow.

In order to minimize the leakage flow an O-ring (7) is arranged in front of the opening to the slot (8) between the parts (2) and (5).

Description

The invention concerns a seal device for sealing off between a pump impeller and an adjacent non-rotating part.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
It is important that the two parts 2 and 5 extend beyond each other a certain distance to secure a good result.
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.

Claims

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.