NZ Hydropower
Mechanical
- Aug 1, 2006
- 4
I'm needing to design a seal on a hydro turbine which will keep oil mist inside, and keep dust out of a fairly large thrust bearing assembly. I'd appreciate some recommendations for seal types that might be suitable. Conditions are as follows:
- 290 mm seal diameter, shaft rotating at 150 rpm, surface speed = 2.3 metres per second (about 450 feet per minute).
- running surface is a fine turned mild steel. This could be sleeved to provide a hardened and ground surface etc if need be.
- axial movement of shaft at seal 1 - 2 mm (1/16").
- runout at seal approx. 0.2 mm (0.008").
- vertical shaft.
- differential pressure is very small. Arises solely from the thermal expansion of the air volume within the bearing housing.
- operating temperature is 40 - 60 degrees Celsius.
Requirements:
- design is simple and robust with minimal maintenance.
- design life > 20 years with routine maintenance once every 2 years.
- seal is able to keep most of the oil mist that forms within the bearing housing contained, or prevent it from entering the surroundings.
- seal is able to mostly exclude fine abrasive airborne particles and stop them entering the bearing oil.
- design must be fully split to allow installation with the shaft in-situ.
- seal outside diameter < 330 mm. Seal length < 60 mm.
The 'standard' solution to this problem as far as I know is to provide a series of 2 non-contacting labyrinth seals around the shaft. A flow of clean air is provided through the space between the 2 seals via an inlet and exhaust port on the seal housing.
I'm wondering if there is a more simple way to solve this problem that would do away with the additional piping and air or vacuum supply. It occurred to me to use a simple felt seal, but I'm not sure how effective this would be, or how to dimension the housing groove correctly. I'd be particularly interested to hear from anyone with direct experience with felt seals, but any help appreciated.
Thanks, James.
- 290 mm seal diameter, shaft rotating at 150 rpm, surface speed = 2.3 metres per second (about 450 feet per minute).
- running surface is a fine turned mild steel. This could be sleeved to provide a hardened and ground surface etc if need be.
- axial movement of shaft at seal 1 - 2 mm (1/16").
- runout at seal approx. 0.2 mm (0.008").
- vertical shaft.
- differential pressure is very small. Arises solely from the thermal expansion of the air volume within the bearing housing.
- operating temperature is 40 - 60 degrees Celsius.
Requirements:
- design is simple and robust with minimal maintenance.
- design life > 20 years with routine maintenance once every 2 years.
- seal is able to keep most of the oil mist that forms within the bearing housing contained, or prevent it from entering the surroundings.
- seal is able to mostly exclude fine abrasive airborne particles and stop them entering the bearing oil.
- design must be fully split to allow installation with the shaft in-situ.
- seal outside diameter < 330 mm. Seal length < 60 mm.
The 'standard' solution to this problem as far as I know is to provide a series of 2 non-contacting labyrinth seals around the shaft. A flow of clean air is provided through the space between the 2 seals via an inlet and exhaust port on the seal housing.
I'm wondering if there is a more simple way to solve this problem that would do away with the additional piping and air or vacuum supply. It occurred to me to use a simple felt seal, but I'm not sure how effective this would be, or how to dimension the housing groove correctly. I'd be particularly interested to hear from anyone with direct experience with felt seals, but any help appreciated.
Thanks, James.
