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That is not to suggest that the two sets of standards are the same for they aren't. The ISO-6431 is a metric standard, the NFPA is imperial measure.
The cylinders covered by ISO-6431 are of the "tie rod" type, and include bore sizes from 32 mm (about 1 1/2" inch) up to 100 mm (or about 4").
These cylinders are of metric dimension, meaning that bores, strokes, port sizes, rod threads and mounting accessories all in metric measure.
Given that an ISO-6431 a cylinder must meet the ISO standard dimensions for that size of cylinder, if you have a cylinder of this type on your equipment now, you should be able to purchase a substitute cylinder of the same bore and stroke size from any other manufacturer and have it "drop in" as a replacement; good news if you don't know where your present cylinder was obtained.
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Many ISO-6431 have "integral" tie rods as shown in the picture unlike older NFPA style cylinders that had tie rods that were not integral to the barrel body. Instead, they had rods that were inserted through the cylinder end caps and attached to the cylinder with nuts at both ends.
The tie rods in an ISO-6431 type cylinder are often extruded as part of the barrel, and tie rod bolts are screwed into mating threads in the cylinder barrel via countersunk through holes in the cylinder end caps.
Current designs of the ISO-6431 cylinder often include unthreaded holes in the barrel and the through-bolts used to attach the end caps to the cylinder barrel are self tapping.
The piston rod diameter will meet the ISO standard for that particular bore size, and normally comes with a male metric thread. ISO standards show that a variety of options for the rod thread are available, though the standard is a male thread.
ISO-6431 cylinders have a wide variety of mounting styles and accessories, including:
As with any cylinder, to improve cylinder life it's important to try to prevent the cylinder piston from "bottoming" on either the rod or rear end caps, by making the tooling reach end of stroke before the piston hits the end of the cylinder. Repeated impact can damage the piston and will sometimes even fracture the rod-to-piston attachment.
Sideloading of the cylinder rod is an absolute "no no"!
If the cylinder application has the potential for sideloading on the end-of-rod tooling and therefore sideloading the rod itself, an alignment coupler should be used.
If an aligment coupler is insufficient to eliminate sideload, the cylinder mounts must be such that the cylinder can "give" as sideloading force is applied to the cylinder rod. Perhaps a rear clevis, or a trunnion mount might be in order.
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