Pneumatic and Hydraulic Polyurethane Seals

One Example of the successful use of polyurethane for sealing is an Oleo-Pneumatic buffer for use on railway rolling stock. The pressures encountered in this application are not particularly high but an efficient seals is of prime importance. In this buffer compressed air or nitrogen is utilized as the spring medium for providing static resistance and recoil, the gas being sealed into the buffer behide the oil by a floating piston. It is therefore very important for the seal carried on the floating piston to be highly efficient throughout the working lift of the piston. Operational experience showed that the original seal in nitrile rubber had inadequate wear resistance and this is one of the main factor in buffer service life. After three years operational experience with polyurethane seals the outstanding properties of polyurethane were quite apparent. Seals examined from these buffers, having operated under the most arduous conditions which would have completely destroyed the nitrile seal, showed virtually no wear.

Polyurethane seals can also be used to advantage in hydraulic pit-props for roof supports and other applications. These props operate at relatively high pressure, but the seal must also prevent leakages at low pressures when the prop is out of operation.

Another use for polyurethane seals in the mining industry is found in the control valve unit of chocks. The seal in this case also acts as a seal for high pressure bleed valve. There is a high velocity flow of hydraulic fluid across the sealing face which rapidly scours nitrile rubber, whereas the polyurethane, being more wear resistant, operates satisfactorily.

Other uses for polyurethane hydraulic seals are found where the equipment is used in dirty condition, such as in the case of earthmoving equipment where the efficient operation of seals is of importance in view of hire charges and cost of down-time arising from failures.