What We Know

Sealparts began when leather was still a serious engineering sealing material: hydraulic cup seals, chevron sets, washers and packings. Wet leather conforms to an imperfect bore in a way a moulded elastomer will not, and it carries lubricant inside the material rather than only on its surface.

It is also an animal product. Thickness varies across a hide. Selection, forming, impregnation and lubrication all change how the finished seal behaves. Leather fails by drying out, by hardening, and by picking up contamination that then acts as an abrasive.

Old machinery still turns up with leather in it. Substituting rubber is not automatically the engineering answer — the groove, the surface finish and the lubrication regime were designed around a material that swells, conforms and holds oil.

• Cup seals
• Chevron packings
• Washers
• Impregnation
• Drying failure
• Identification from samples

Warble fly larvae burrow through the backs of cattle and leave holes in the hide. For the leather trade those holes are scrap. For anyone cutting sealing washers and cups out of hides, an agricultural pest became a materials-yield problem: fewer usable areas per hide, more inspection, higher cost, and a real risk of a defect ending up inside a finished part.

Warble fly was eradicated from UK cattle in the 1980s. Modern engineers never meet the problem. It is worth recording because it is a clean example of something that still applies: natural and semi-natural materials carry variation that has nothing to do with engineering intent, and inspection exists to catch it.

Drawing board, graph paper, vernier, micrometer, radius gauge. Seal sections drawn enlarged — five or ten times — so that a lip angle or a heel radius could actually be seen and argued about. Interference, groove depth and material movement calculated by hand and written in the margin.

Engineering existed before software made it tidy. The arithmetic was slower, so fewer options were explored and each one was thought about harder.

Full-size cut-outs, paper templates and cardboard sections were how a gland arrangement got explained to a customer or a toolmaker before anyone committed to tooling. Cheap, fast, and unambiguous in a way a verbal description is not.

There is nothing romantic about it. The tools changed. The need to understand the problem before spending money on it did not.

Pencil → drawing board → 2D CAD → 3D CAD → SolidWorks → simulation → rapid prototyping → digital manufacturing

Each step increased capability and speed. None of them replaced judgement. A wrong assumption modelled in 3D is still a wrong assumption, produced faster and presented more convincingly.

The most common real enquiry we get is an old seal in a jiffy bag. It may be worn, hardened, swollen, torn, flattened, chemically attacked, missing sections, covered in oil and decades old. No drawing. No identifiable manufacturer.

A worn sample still carries evidence:

• Original geometry, inferred from the unworn faces
• Lip direction, and therefore pressure direction
• Approximate interference and squeeze
• Material family, from hardness, feel, cut surface and behaviour
• Operating environment, from swelling, glazing or heat damage
• Groove relationship and back-up arrangement
• Likely failure mechanism
• Whether it matches a standard profile or was bespoke

Measurement of a used elastomer gives you a number. Interpretation gives you the part.

Manufacturer numbers, machine-builder numbers, distributor references, superseded numbers, customer stock codes, drawing numbers, numbers that refer to an assembly or a kit rather than a seal, and numbers transcribed wrongly at some point in the last thirty years.

The same seal often exists under several references. Two parts sharing a reference are not necessarily the same compound.

A part number is evidence. It is not necessarily the answer.

Discontinued profiles, manufacturers no longer trading, catalogues out of print, machines older than the people maintaining them. What usually survives is the functional geometry, and that can be reproduced: reverse engineered from a sample, matched to a current equivalent profile, or machined as a one-off in a modern material.

The work is deciding which dimensions are functional and which are historical accident.

• Rod seals
• Piston seals
• Buffer seals
• Wipers
• Wear rings
• Guide rings
• O-rings
• Back-up rings
• Static seals

Around them: bore condition, rod condition, surface finish, extrusion gap, working pressure and spikes, side loading, contamination, installation damage, trapped pressure between seals, and groove condition after a previous failure.

See product focus for individual profiles.

Different problem to hydraulics. Pressures are low, cycle rates are high and friction matters more than sealing force. Breakaway friction, stick-slip on slow-moving actuators, lubricated versus dry air, wear over millions of cycles, cushioning seals, compact cylinders and the leakage rates automation equipment will tolerate.

The most standardised sealing component in existence, and still the one most often specified incorrectly.

• Metric
• Imperial
• BS 1806
• AS568
• JIS B 2401
• Non-standard
• Cord
• Vulcanised
• Moulded
• Encapsulated

The engineering sits in squeeze, stretch, groove fill, extrusion gap, back-up ring use, pressure direction, compression set, temperature, chemical compatibility, dynamic versus static duty, surface finish and installation damage.

O-ring reference and enquiry · Japanese (JIS) O-rings · Sizes · Materials

JIS O-ring series do not interchange with BS or AS568. Japanese hydraulic and pneumatic profiles use their own geometry and their own groove dimensions, and Japanese machine tools are full of them.

A European seal of the same nominal bore and rod size may fit the groove and still be wrong — different heel width, different lip angle, different squeeze, different back-up assumption. We keep Japanese catalogue data specifically so that substitution is a decision rather than a guess.

Sakagami · Sakagami profile summary

CNC machining centres, lathes, grinders, hydraulic clamping, tool changers, rotary tables, coolant and lubrication systems, slideway protection. Coolant chemistry is frequently the deciding factor on material, not pressure or temperature.

Keeping contamination out is often more important than keeping fluid in. Most rod seal failures we examine started as a wiper problem.

• Metal-cased
• Elastomer
• Polyurethane scrapers
• Double-lip
• Swarf
• Dust
• Mud
• Coolant

Wear resistance, extrusion resistance and abrasion resistance well beyond conventional rubber, which is why it dominates high-pressure hydraulic rod and piston sealing. Hardness range is wide. Behaviour at low temperature varies. Polyester types hydrolyse in hot water; polyether types tolerate it far better.

“Polyurethane” does not describe one material.

The default hydraulic elastomer: mineral oils, moderate temperature, good mechanical properties, low cost. Limited by temperature, ozone and weathering, and by ageing in hot oil. Acrylonitrile content changes both oil resistance and low-temperature flexibility, and the two move in opposite directions.

High temperature, oils, fuels and a wide range of chemicals — with real limitations at low temperature and against steam, hot water, amines and some brake fluids. Different FKM types differ substantially in chemical resistance.

“Viton” is a brand name used loosely. The compound, not the nickname, determines what the seal survives.

Water, steam, glycols, weathering, ozone and phosphate-ester and glycol-based brake fluids. Not compatible with petroleum oils and greases — the most common single material error we see in the field, usually because a black seal was assumed to be NBR.

Low friction, exceptional chemical resistance and a temperature range no elastomer reaches. Used as machined seals, energised with a spring or an O-ring, and heavily modified with fillers — glass, carbon, bronze, graphite, polymer. Creeps under sustained load, needs care on installation, and demands a good counterface.

PTFE grade reference

NBR is not one material. Polyurethane is not one material. PTFE is not one material. FKM is not one material.

Compound formulation, hardness, fillers, plasticisers, cure system and manufacturer-specific recipes all change temperature limits, media compatibility, compression set and wear. Two seals correctly described as “NBR 70” can behave differently in the same cylinder.

A blue seal is not necessarily the same material as another blue seal. A black seal is not necessarily NBR. A green seal is not necessarily FKM. Pigment is a manufacturer’s identification convention, and conventions differ between manufacturers and change over time.

Colour can be evidence. It cannot be relied upon as the specification.

• Extrusion
• Nibbling
• Compression set
• Hardening
• Softening
• Swelling
• Cracking
• Abrasion
• Cutting
• Twisting
• Spiral failure
• Heat damage
• Chemical attack
• Lip wear
• Installation damage

Each of those has a characteristic appearance and points at a different cause. Spiral failure is a friction and lubrication problem. Nibbling is a clearance problem. Uniform hardening is a temperature or chemical problem.

A failed seal is evidence. Do not throw it away before examining it.

Failure analysis

A leak is a symptom. The seal is the component that shows it first.

• Scored or pitted rod, damaged chrome
• Worn bore or oval cylinder
• Incorrect or damaged groove
• Excessive extrusion gap from worn guide rings
• Bearing failure, side loading, misalignment
• Contamination the wiper cannot handle
• Pressure spikes beyond design
• Installation damage
• Temperature beyond the material limit

Fitting a new seal to an unchanged machine reproduces the failure, usually faster the second time.

Too rough and the seal abrades. Too smooth and the lubricating film breaks down and the seal runs dry. Directionality matters — a ground and polished rod behaves differently from a turned one, and machining lead can pump fluid straight past a lip.

A new seal on a damaged rod fails again, and the customer concludes the seal was poor quality.

Seal tolerance, housing tolerance, shaft tolerance, groove tolerance, and the stack-up of all four in the same direction on a bad day. Add manufacturing variation, thermal expansion of dissimilar materials and batch-to-batch variation in the compound.

A few hundredths of a millimetre decides whether a seal has squeeze, no squeeze, or an extrusion gap.

Continuous pressure is rarely what kills a seal. Spikes, reversals and pressure trapped between two seals do. Extrusion resistance depends on gap, material hardness and temperature together, not on any one of them.

The catalogue maximum is a test-rig figure at a stated gap and temperature. It is a starting point, not a promise.

Breakaway friction, running friction, stick-slip, seal preload, lubrication regime, surface finish, material and cycle rate. Everything that increases sealing force increases friction, heat and wear. Every sealing arrangement is a compromise between leakage and life.

Continuous rating, peak excursions, cold start-up, ambient conditions, fluid temperature and heat generated at the lip itself — which can be well above bulk fluid temperature on a fast, high-pressure cylinder. Low temperature makes elastomers stiff and glassy; high temperature accelerates compression set and chemical attack.

Hydraulic oils, water, glycols, fuels, solvents, cleaning chemicals, coolants, food-industry media and — most often overlooked — mixtures, plus whatever was used to flush the system last.

Compatibility charts are generated at a stated temperature with a pure fluid. Raise the temperature and the rating changes. Treat the chart as a filter, not as a verdict.

Many seals fail before the machine is ever started.

• Sharp edges, circlip grooves, ports and threads on the way in
• Twisting a rectangular section during fitting
• Wrong orientation — a lip facing the wrong way seals nothing
• No lubrication on assembly
• Overstretching, folding or forcing a polyurethane profile cold
• Contamination introduced during assembly
• Not using an installation cone or sleeve where one is required
• Warming a profile where the manufacturer permits it — and not where they don’t

Ozone, UV, heat, humidity, deformation and time. O-rings hung on nails and stretched for years. Boxes stored next to electric motors, which generate ozone. Old stock that measures correctly and has already lost its elasticity.

ISO 2230 gives storage conditions and shelf-life periods by material group. FIFO, sealed packaging and dated stock matter more than most stores realise.

Packaging used to mean a bag, a box and a label. It now carries batch traceability, material declarations, country of origin, and compliance with packaging material regulation — the EU PPWR being the current driver for anyone shipping into Europe.

Packaging became part of industrial compliance rather than just transport.

Old drawings with missing tolerances, handwritten amendments, imperial dimensions, unclear revision levels and three different numbering systems on the same sheet. The skill is deciding which dimensions actually control seal function and which were copied forward for decades without anyone checking.

Sealparts has worked right through the transition. Inch shafts in metric housings. Converted machinery. Nominal metric dimensions that are suspiciously close to a round imperial size.

One inch is 25.4 mm. That does not mean a 25 mm seal fits, and it does not mean a 25.4 mm seal was ever made for that groove.

Vernier, micrometer, optical comparator, pin gauges, radius gauges. Measuring a flexible, worn, swollen component is not the same activity as measuring a machined part: the vernier deforms it, the sample has taken a set, and the number you read is the current state, not the original.

Measurement gives data. Interpretation gives the specification.

One-offs, development quantities, machined prototype profiles, trial materials, rig testing, revised geometry, then small batches. The first design is rarely the final design, and finding that out on a machined prototype is cheaper than finding it out on a mould tool.

Prototyping and small-batch production

Compression, transfer and injection tooling. Tool wear, tool identification, tool ownership, old tools that still exist somewhere, recut tools and prototype tools that were never intended for production. For low-volume seals the tooling question is economic before it is technical.

CNC-machined polyurethane, PTFE, POM and rubber profiles with no dedicated tooling. Days rather than weeks, any diameter, any quantity from one, and the practical answer for obsolete parts and large diameters. Material choice is narrower than moulding, and unit cost does not fall with quantity in the same way.

Tooling, compound preparation, cure, flash removal, shrinkage allowance, dimensional variation between cavities and batches, and inspection. Correct for production quantities and for profiles where the moulded material outperforms anything machinable.

Industrial maintenance rarely needs 10,000 parts. It needs two, before Friday, for a machine that was discontinued in 1994. Obsolete equipment, prototypes, experimental rigs, specialist OEMs and development programmes all live in that quantity band, and most of the supply chain is not built for it.

Large O-rings, vulcanised joints, machined rings and split arrangements. Measurement becomes harder, handling and packaging become real constraints, and joint integrity on a vulcanised ring becomes the thing to inspect.

A seal cannot always be understood in isolation. What machine is it from? What does it do? What moves? What fluid? What pressure? What temperature? What failed, how quickly, and what changed just before it did?

Two identical-looking seals can require different materials or geometry because the duty differs: frequency of movement, pressure, temperature, media, environment, expected life, consequence of a leak, and how difficult the machine is to strip.

A weeping seal on an accessible workshop press is an inconvenience. The same seal offshore is a shutdown.

Where a lot of this started. Tractor hydraulics, rams, loaders and implements, working in mud, water, dust and grit, stored outdoors, repaired in a yard rather than a clean workshop, and expected to run again the next morning. Contamination exclusion outranks almost everything else.

Excavators, loaders, lifting equipment. Shock loading, pressure spikes, rod damage from site debris, heavy-duty polyurethane sealing and wipers doing most of the protective work. Duty cycles are intermittent; abuse is continuous.

Presses, production machinery, power units and custom cylinders. Long duty cycles, planned maintenance, and a strong economic argument for getting the seal specification right once rather than replacing it every quarter.

The manufacturer disappeared decades ago. The drawing no longer exists. The manual is missing. The original distributor is gone. The seal carries no useful marking. The only engineering evidence is the machine itself.

And the machine still needs to work.

CNC, automation, robotics, high-speed pneumatics, advanced materials, electronic monitoring and predictive maintenance. Cleaner, faster, better instrumented.

The fundamentals are unchanged: squeeze, gap, finish, media, temperature and installation.

Long involvement with Japanese sealing products has taught us specific, practical things: part families that stay in production for decades, dimensional consistency across batches, catalogue data organised around machine applications rather than around profile codes, and JIS standards that quietly govern a great deal of machine-tool sealing in Europe.

It also taught us to cross-reference carefully, because the European cataloguing tradition organises the same information differently.

Italian manufacturing gave us the opposite strength: a large library of specialist hydraulic and pneumatic profiles, willingness to produce non-standard geometry, and short routes from a drawing to a sample. Useful for European OEM applications and for anything that does not appear in a standard catalogue.

Tecnolan · Tecnotex

Knowing seals also means knowing how industrial parts actually move: manufacturer, distributor, OEM, machine builder, stockist, maintenance engineer, end user. International shipping, customs, country of origin, lead times, minimum order quantities, the economics of small orders, and obsolescence arriving without notice.

A catalogue gives you dimensions, material, pressure, temperature and a part number. It does not tell you:

• Why the previous seal failed
• Whether the rod is damaged
• Whether the machine has been modified
• Whether the old sample has swollen
• Whether the original part was ever correct
• Whether a different profile would work better

Searchable catalogues, manufacturer databases, CAD downloads, technical PDFs, cross-reference tools, digital photography, drawings sent across the world in seconds, and obscure part numbers that can now at least be searched.

More information did not automatically produce better diagnosis. It produced faster access to plausible wrong answers.

It is genuinely useful for searching large technical archives, reading and comparing documents, translating manufacturer literature, extracting dimensions from tables, and finding patterns across historic references. We use it for exactly that.

It accelerates investigation. It does not remove the requirement to understand the physical application, and it will produce a confident part number for a seal that does not exist.

A good photograph of a failed seal is often worth more than a paragraph of description. Lip condition, wear pattern, direction of damage, housing condition, part markings, packaging labels and the assembly it came out of — with something in frame for scale.

Photographs also accumulate. A visual archive of failures is a diagnostic tool.

Old catalogues, manufacturer literature, drawings, price lists, technical manuals, samples, correspondence and obsolete part-number lists.

Something being old does not make it useless. Sometimes the old catalogue is the only surviving map.

• What is it sealing?
• What moves — rod, piston, housing?
• Which direction does it move, and how fast?
• What pressure, continuous and peak?
• What temperature, continuous and at start-up?
• What media, including anything used to flush the system?
• What size — and measured how?
• What material, and on what evidence?
• What is the groove, and is it undamaged?
• What is the shaft or bore condition?
• What failed, and how did it fail?
• How long did it last?
• What was fitted before?
• Has anything changed — fluid, duty, temperature, supplier?
• Is the sample swollen? Is it worn?
• Is the part number original, or transcribed?
• Is the machine standard, or has it been modified?
• How many are required, and by when?
• Does it actually need to be identical?

• Do not assume the old seal was correct.
• Do not assume black means NBR.
• Do not assume green means FKM.
• Do not assume the drawing is current.
• Do not assume the part number was copied correctly.
• Do not assume the sample retains its original dimensions.
• Do not assume catalogue maximums equal application limits.
• Do not assume leakage means the seal is faulty.
• Do not assume a newer material is automatically better.
• Do not assume an equivalent-looking profile is equivalent.

• Leather
• Synthetic elastomers
• Polyurethane development
• PTFE systems
• Improved machining
• CNC
• CAD
• 3D CAD
• SolidWorks
• Digital measurement
• Rapid prototyping
• Machined seals
• Email
• Digital photography
• Online catalogues
• Search engines
• Global supply chains
• Modern compliance
• AI

• Dimensions still matter.
• Material still matters.
• Surface finish still matters.
• Pressure still matters.
• Temperature still matters.
• Contamination still matters.
• Geometry still matters.
• Installation still matters.
• And asking the right question still matters.