DYNAMIC WEAR RINGDESCRIPTIONThe present invention relates to a dynamic wear ring, particularly for use with centrifugal pumps and even more particularly with centrifugal pumps operating under high pressure and having journal bearings.
Traditionally wear rings have been used in different pumping applications to reduce internal leakage within the pumps. They are positioned in the gap between impeller and pump housing and their construction is adapted to the geometry of the gap. The radial clearance depends on several factors including the production tolerances of the parts, the bearing clearance, and safety considerations as well as on the run-out in the pump housing and the bearing brackets.
For the high pressure pumps used in modern applications, it becomes even more critical to ensure the minimum possible wearing clearances to improve efficiency.
According to the present invention there is provided a sealing arrangement for sealing a wear ring against a pump housing, the sealing arrangement comprising:a first recess on a first surface of the wear ring, housing a static O-ring seal, anda second recess on a second surface of the wear ring perpendicular to the first surface and housing a dynamic seal,wherein the static O-ring seal is arranged to guide and stabilize the wear ring, and has no sealing functions.
Preferably the diameter of the dynamic O-ring seal and the stiffness or lack of resiliency of the static O-ring is chosen to guide and stabilize the wear ring dynamically.
According to a preferred embodiment of the present invention at least one tangentially locking guiding pin is provided on the wear ring to prevent the wear ring from rotating, and a balancing hole passes through the wear ring for reducing friction forces, and balancing the static 0ring.
A sealing arrangement according to the present invention allows for an increase in volumetric efficiency, particularly in high pressure pumps. It takes advantage of the radial forces created in the wear ring gap.
For a better understanding of the present invention and to show how the same may be carried into effect, reference will now be made to the accompanying drawing in which the single figure shows a cross section through a wear ring incorporating a sealing arrangement according to the present invention.
A dynamic wear ring 1 is located in a gap between a wear ring housing 4 and an impeller shroud 11. A dynamic 0ring 2 rests in a recess 12 in a side surface of the wear ring 1 and serves to control the back pressure on the wear ring 1. A static O-ring 3 is located in a recess 14 in an upper surface of the wear ring perpendicular to the surface housing dynamic O-ring 2. The stiffness of the static O-ring 3 and its frictional adherence to the adjacent surface 12 stabilizes the wear ring 1. There is also a fluid film between the wear ring 1 and the wear ring housing surface 15, which has a hydrostatic damping effect and further assists stabilization of the wear ring radially.
The static O-ring 3 is balanced against the adjacent surface 15 of the housing 4 by the hydrostatic pressure in the gap between the pump impeller shroud 11 and the casing wall. The diameter of the dynamic O-ring determines the friction force.
A passage 17 extends through the wear ring and acts to balance the friction forces. There are preferably a plurality of such passages and they may be formed by drilling through the wear ring 1.
A guiding pin 6 is located to lock the wear ring 1 tangentially to the adjacent surface 10 of the housing 4.
A Seeger locker 5 is located in the housing 4, to secure the wear ring during handling and transportation.
During operation the hydrostatic pressure created by the impeller will press the wear ring axially against surface 12 in the housing.