High Pressure Hydraulic Swivels
Using Kalsi Seals in High Pressure Hydraulic Swivels
This page highlights an improved hydraulic swivel for use with Kalsi-brand rotary shaft seals. This high pressure swivel design uses our simple stacking housing arrangement to accommodate our patent-pending floating backup rings. These novel backup rings provide the smallest possible clearance at the extrusion gap while avoiding the risk of seal-damaging, heavily loaded metal-to-metal contact. This is accomplished by providing the backup rings with hydraulic force balance in the axial direction, which allows them to float laterally to follow any mandrel runout that may be present. By minimizing the extrusion gap clearance, these floating backup rings maximize the high pressure performance of the swivel seals. In a 1,000 hour, 51.7 MPa (7,500 psi) test of 69.85mm (2.75”) ID Plastic Lined Kalsi Seals at 255 surface feet per minute, the seals and backup rings showed little evidence of use. This is truly remarkable performance.
An Overview of a Hydraulic Swivel Design for Extreme Pressure Service
The expandable drawings included below show some of the construction details of hydraulic swivel for extreme high pressure service. Detailed design recommendations for hydraulic swivels are provided in our rotary shaft seal handbook.
The left-hand image, below, shows overall construction details of a hydraulic swivel. The pressure housing assembly consists of a stack of housings that are retained together by a pattern of bolts. The bearings are contained within housings that are bolted to opposite ends of the pressure housing assembly. In this arrangement, the hydraulic fluid pressure cannot create pressure breathing that increases the mounting fit of the bearings. This helps to minimize runout of the shaft, and accompanying seal extrusion damage. The stacked housings are relatively simple to machine, and are piloted together by axially short, bind-proof pilots that assure easy assembly. The stacked housing design eliminates the use of radial O-rings, which cause significant assembly difficulty, and are prone to failure in high pressure service conditions.
The middle image, below, shows the hydraulic circuits of the swivel. Each high pressure swivel seal is supported by a floating backup ring that is captured in position by the stacked housings. Anti-rotation pins are used to prevent the backup rings from rotating with the shaft. Each backup ring is guided by a close journal bearing-type fit to the shaft that also defines the extrusion gap clearance that the swivel seals are exposed to. Cross-drilled hydraulic fluid passages communicate pressure to the back side of each backup ring, providing the backup rings with axial force balance. The axial force balance leaves the backup rings free to float laterally to align themselves on the shaft, even in situations where a significant degree of shaft runout is present. Our seal handbook includes an enlarged view of the hydraulic fluid passages, and provides comprehensive instructions on how to design a high pressure hydraulic swivel.
The right-hand image shows an oil communication passage that provides communication between the sealed bearing regions. The oil communication passage also serves as a drain that accommodates the hydrodynamic pumping related leakage of the Kalsi-brand hydraulic swivel seals. The leakage is returned to the hydraulic fluid reservoir.