O-rings and Back-up Rings
The standard static sealing element, plus the anti-extrusion rings that support it at pressure. Most of a hydraulic system's joints are sealed this way, and most of its mystery leaks start here. SES holds the range as an authorised SKF distributor, covering size standard ISO 3601 metric and inch series; cord sections From about 1 mm to over 10 mm; materials NBR, HNBR, FKM, EPDM, silicone, perfluoroelastomer; hardness Commonly 70 to 90 Shore A depending on pressure. Executions include NBR o-rings, FKM o-rings, EPDM o-rings for water and phosphate ester, solid PTFE back-up rings, among others. It is specified most often into cylinder end cap and gland joints and valve block face joints and cartridge valve cavities. Every part is genuine SKF through official channels, with designation, specification and options confirmed against your duty before it ships — supplied from Kolkata and our branch network, with breakdown cover that does not sit in an inbox.
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From integrated steel plants to power utilities and EPC majors — the works that cannot afford a counterfeit part specify through SES.
Duty
Mainly static; limited dynamic use
Sizes
Wide standard series to ISO 3601
Materials
NBR, HNBR, FKM, EPDM, silicone
Back-up rings
PTFE or POM, anti-extrusion support
Where it runs.
You will find O-rings and Back-up Rings in the parts of a plant where this particular duty actually occurs. In practice that means cylinder end cap and gland joints, valve block face joints and cartridge valve cavities, pump and motor port connections, and equally accumulator and manifold sealing, instrument and gauge fittings on hydraulic lines, static joints on lubrication system pipework. What links them is the duty rather than the machine name — duty: Mainly static; limited dynamic use. If your installation is not on that list it matters less than you would think: the operating condition decides the specification. Send us the load, the speed, the running temperature and the environment it runs in, and we will match it to the right execution in the SKF range and confirm what is in stock.
Specify it against the duty.
Specification here follows the operating condition, not the catalogue. Pressure is high and the joint has a visible clearance gap — A back-up ring on the low-pressure side. Without it the O-ring extrudes into the gap and the nibbled edge shows as a fine bleed that no torque will stop. The joint sees phosphate ester or a synthetic fluid — EPDM or another compatible compound and keep it strictly out of mineral oil systems. A mixed-up store bin is a very common cause of repeated joint failures. The system runs high-pressure gas or decompresses rapidly — A compound rated for explosive decompression. Ordinary nitrile absorbs gas under pressure and blisters internally when the pressure drops. Where two of those apply at once, specify for the harsher of the two — under-specifying is what puts the part back on the bench a month later. Send us the duty and we will confirm the execution.
Ordering this from SES.
Store O-rings flat, in the dark, away from motors and welding sets. Ozone from an arc or a brush-gear motor cracks nitrile on the shelf, and a ring that fails on commissioning was often ruined months before it was fitted.