Development of John Crane Flexible Metallic Packing
Seldom has an engineering invention or discovery attracted so much attention and created so much interest among operating engineers as has the now well known “John Crane” flexible metallic packing. “John Crane” packing was invented by an operating engineer named John Crane in the early Spring of 1912. John Crane then had charge of a large power plant and was directly responsible for maintenance and repair costs. His first object was to develop a permanent packing. From actual experience with his outside packed plunger feed pump, he knew that soft packings ordinarily lasted only from four to five months, depending upon the condition of his plungers. He noticed that where metal and fabric were combined in packings, such as metal studs or metal segments, the life of such packing was lengthened. He noticed also that these metals were not affected by heat or water, while the soft packings were. And not only did he notice that the metal lengthened the life of the packings, but it seemed to polish the plunger, and hence the idea came to him of an all metallic packing. Flexibility and compressibility were also desirable, necessitating some mechanical combination. Of course it was possible to take metal and shred it and twist it in the form of rope or braid it in the form of packing. This would give the flexibility. But would it be a packing through which pressure could not pierce? After much thought and experimentation, John Crane evolved the idea of taking long, thin, continuous strips of metal foil and wrapping it spirally round and round, back and forth, impregnating each sheet with a layer of lubricant to permit the sheets to slide on each other and to allow bending about the smallest diameter and giving it a compressibility sufficient to compensate for wear and sufficient to control any ordinary pressure. These spirally wrapped sheets, he found, formed perfect harriers through which pressure could not pierce and formed a strong, durable construction. The idea of simplicity did not get away from John Crane. He therefore used soft metal which could be cut with a knife, took any form or shape under pressure of the gland and bent about the plunger very easily. Reduction of rod friction and elimination of wear were also prominently borne in mind when this packing was developed. That is why John Crane selected the best anti-frictional metallic sheet combination with babbitt alloy he could find. A mechanical construction of these same babbitt sheets spirally wrapped with additional reservoirs of lubrication between each sheet, naturally was successful in eliminating the wear on the rod. “John Crane” products are now made up in all kinds of forms, die pressed, hard pressed, straight lengths, rings, coil form, spiralled from 1-32 in. thick to 2 in., suitable for steam, air, ammonia, hot or cold water, high or low pressure, hydraulic, oil. and acid service. The “John Crane” line has been steadily developing and today any combination of metal alloys for special services can be secured, either in form of a packing or in a gasket. Fig. 1 is merely smooth babbitt sheets, thoroughly lubricated. wrapped spirally, forming an allmetallic, flexible, compressible, simple and lasting packing. Fig. 2 shows how “John Crane” looks in ring form, and Fig. 3 shows it in coil form. Rings are generally preferred for large plungers, whereas coils are used in smaller work, as in valves, traps, small steam rods, etc.