Know Your Seal

A plain-English guide to hydraulic & pneumatic seals

What each product does, where it's used, and which material suits your application — so you order the right part the first time.

Product Types

Thirteen core product families, each solving a different job inside a hydraulic cylinder or rotating shaft.

Wear Rings (Guide Rings)

Support elementNon-sealing

A wear ring doesn't seal pressure — its job is to centre the piston or rod inside the cylinder bore, carrying the side-load so metal never touches metal. This single-handedly protects the actual sealing elements and the cylinder wall from wear, extending the life of the whole assembly.

Used in: piston grooves and rod glands of hydraulic cylinders, especially under side-load or in long-stroke applications. Typical material: FRPR (phenolic resin fabric), bevel cut, 2–3 mm thickness.

Wear Strips

Support elementSold per metre

The same guiding function as a wear ring, supplied as a continuous strip rather than a finished ring. Useful for large-bore cylinders or where a custom length needs to be cut and fitted on site, rather than ordering an exact-diameter ring.

Used in: large or custom-bore hydraulic cylinders. Typical materials: FRPR or Bronze-filled PTFE, measured by thickness × width.

Oil Seals

Sealing elementRotating shafts

An oil seal rides against a rotating or reciprocating shaft, holding lubricating oil in and keeping dirt and moisture out. It comes in two forms: metal-cased (the metal case is exposed on the outside, with the elastomer bonded only on the inside and at the lip) and metal-covered (the metal case is fully jacketed in elastomer, with no bare metal visible). Both types share an elastomeric inner lip backed by a quality garter spring, which keeps constant lip pressure on the shaft even as the rubber wears slightly over time.

Used in: gearboxes, pumps, motors, and any rotating-shaft housing that needs to retain oil. Typical materials: NBR (general purpose), FKM/Viton (high heat & chemical resistance), VMQ/Silicone (temperature extremes).

Piston Seals

Sealing elementSingle or double acting

Single acting seals (often U-cups) hold pressure from one direction only — common where the cylinder only needs to push, not pull, under full pressure. Double acting seals have a symmetric profile that holds pressure equally from both sides, needed when a cylinder works under load in both directions. A PTFE seal paired with an O-ring energiser (often branded Glyd Ring or OMKMR) gives low-friction, high-pressure performance where a rubber U-cup would wear too fast.

Used in: the piston groove of hydraulic cylinders. Typical materials: PU, PU+NBR, Bronze-filled PTFE+NBR, or heavy-duty composite sets (NBR+PE+POM) for double-acting, high-cycle applications.

Rod/Piston Seals

Sealing elementDual-purpose

A single seal profile engineered to fit either the rod gland or the piston groove of the same cylinder family. This is a practical stock-reduction choice — one part number covers two positions, which simplifies spares inventory for maintenance teams and OEMs alike.

Used in: either position, same cylinder design. Typical material: PU.

Rod Seals

Sealing elementRod gland

The most critical sealing element in a hydraulic cylinder. It sits in the gland and keeps hydraulic fluid inside as the rod moves in and out. The range includes single-acting lip seals with an asymmetric profile, buffer seals that sit ahead of the main seal and protect it from pressure spikes, PTFE-based gland seals with an NBR energiser for low friction, and stacked Vee-ring sets between male and female adapters.

Used in: the rod gland of hydraulic cylinders. Typical materials: PU, NBR, and Bronze-filled PTFE with an NBR energiser.

Wipers (Dust Seals)

Protective elementHydraulic

A wiper scrapes dirt, dust, moisture and debris off the rod as it retracts, so contamination never reaches the seals inside the cylinder. Metal-clad wipers (MC) add a metal case around the wiping element for a firm, secure press-fit in the gland. Many wipers have a stepped outside diameter, so they are sized as ID × OD × groove height / total height: the first height is the groove the wiper presses into, the second is its overall height.

Used in: the rod end of hydraulic cylinders. Typical materials: PU, NBR, HYTREL, FKM (for extreme heat and aggressive environments), and metal-clad MC/PU and MC/NBR.

O-Rings

Static & dynamic sealingSold by size

The simplest and most widely used seal in the world: a round-section elastomer ring that is squeezed into a groove to block leakage. O-rings are specified by just two numbers — the inner diameter (ID) and the cross-section (CS), both in millimetres — so finding the right one is a matter of measuring.

Used in: hydraulic and pneumatic fittings, valves, pumps, cylinder end caps, flanges and covers. Materials: NBR 70 for mineral oils and general industrial duty (up to about 120 °C); FKM 75 for high heat (up to 210 °C), aggressive chemicals and synthetic fluids. X-rings (quad rings) can also be supplied on request. Order quantities: small sizes are supplied in packs — the minimum order is shown on each product in your basket.

Combi Rod Seals (Pneumatic)

PneumaticSeal + wiper in one

A combi rod seal puts two jobs into a single profile: a dynamic sealing lip that keeps compressed air inside the cylinder, and a wiper lip that scrapes dust, moisture and debris off the rod as it retracts. One part, one groove, dual protection — which is why it is the standard rod-end seal in compact pneumatic cylinders.

Used in: pneumatic cylinders and actuators in automation, packaging and assembly equipment. Typical material: PU (polyurethane) — excellent wear resistance for fast, repetitive strokes. Rated up to 16 bar and 80 °C.

Cushion Seals (Pneumatic)

PneumaticEnd-of-stroke damping

Fitted in the end-cap of a pneumatic cylinder, the cushion seal controls how air escapes as the piston nears the end of its stroke. By throttling the exhaust it slows the piston gently, cutting the shock, noise and wear that come from a hard stop.

Used in: pneumatic cylinders on automation, packaging and assembly lines where fast strokes need a soft landing. Typical material: PU (polyurethane) — tough and wear-resistant. Rated up to 16 bar and 80 °C.

Piston U-Cup Seals (Pneumatic)

PneumaticPiston seal

A directional lip seal with a U-shaped cross-section, fitted in the piston groove of a pneumatic cylinder. Air pressure presses the two lips outward — one against the bore wall, one against the groove — so the harder the air pushes, the tighter it seals. One U-cup holds pressure in one direction, so double-acting cylinders use one on each side of the piston.

Used in: pneumatic cylinders on automation, packaging and assembly equipment. Materials: PU for outstanding wear resistance and long life; NBR for economical general-purpose duty. Rated up to 16 bar, with PU to 80 °C and NBR to 100 °C.

O-Ring Kits (Assortments)

Hydraulic & pneumaticWorkshop stock

An O-ring kit is a compartment box holding an assortment of O-rings in the sizes most often needed on the shop floor. Keeping a kit at hand means a failed O-ring can be replaced on the spot, without waiting for a single size to be ordered. Each box comes with a size list, and the full contents of every kit are shown in our store.

Standards: AS568 (inch series), JIS and Metric, each in 30 sizes. Materials: NBR70 (nitrile) for oils, fuels and hydraulic fluids; FKM75 for heat and aggressive chemicals.

Chevron Packing Sets (Vee Packing)

Rod & pistonSelf-tighteningHydraulic

A chevron set is a stack of V-shaped rings clamped between a male and a female adapter. As system pressure rises, the rings are pushed open against the rod or bore, so the seal tightens itself the harder the pressure works. The stack height and number of rings can be matched to the pressure, and because the set is assembled from separate rings it copes well with wear, shock loads and large diameters.

Used in: heavy hydraulic cylinders, presses, injection and die-casting machines, and large-bore cylinders — the same set serves as either a rod seal or a piston seal. Typical material: PU (polyurethane) rings with matching adapters, rated to 300 bar and 110 °C.

Materials — What They're Made Of

The rubber or polymer compound determines pressure rating, temperature range, chemical resistance, and cost. Here's how to think about each one.

NBR (Nitrile)

The everyday workhorse — good resistance to mineral oils, reasonable cost, solid mechanical strength. The default choice unless a specific condition rules it out.

Typical range: −30°C to 100–120°C

FKM (Viton)

Premium compound for high heat and aggressive fluids or chemicals that would degrade NBR quickly. Costs more, lasts longer in demanding conditions.

Typical range: −20°C to 200°C+

VMQ (Silicone)

Handles extreme temperature swings — both very hot and very cold — better than almost anything else, but has lower mechanical/abrasion strength, so it's chosen for the temperature range, not for toughness.

Typical range: −55°C to 200°C+

PU (Polyurethane)

Outstanding resistance to abrasion and extrusion under high pressure, which is exactly what a dynamic piston or rod seal needs. The standard choice for high-pressure hydraulic sealing.

Typical range: −20°C to 110°C

PTFE (often bronze-filled)

Extremely low friction and chemically near-inert, but not elastic on its own — so it's usually paired with an NBR or FKM O-ring underneath to provide the sealing force. This combination (often called a Glyd Ring or OMKMR seal) suits high-speed, high-pressure, low-friction duty.

Typical range: −40°C to 200°C+

FRPR (Phenolic Resin Fabric)

A fabric-reinforced resin used specifically for wear rings and wear strips — not a sealing material at all, but prized for being dimensionally stable, low-friction, and tough enough to carry side-load for years without scoring the cylinder bore.

Non-sealing / structural use

Bronze-filled PTFE

PTFE with bronze powder blended in for extra load-bearing strength — used in wear strips and in composite piston seals where both low friction and high mechanical strength are needed together.

High load-bearing capacity

Composite blends

Combinations like PU+NBR or NBR+PE+POM pair a sealing rubber with a harder backing material, giving both a tight seal and extra resistance to extrusion — common in heavy-duty, double-acting piston seal sets.

Application-specific performance

HYTREL

A tough thermoplastic polyester elastomer. It is firmer and more abrasion-resistant than rubber and resists hydraulic fluids well, so it is used where a wiper or support element must hold its shape and resist wear.

Typical range: about −40°C to 120°C

Metal-clad (MC/PU, MC/NBR)

A wiper with a metal case around a PU or NBR wiping element. The case gives a rigid, secure press-fit in the gland while the elastomer does the wiping. "MC" in a part description stands for metal clad.

Temperature range depends on the elastomer

Choosing the Right Seal

Three questions settle most selections:

1. What's the application? Hydraulic (oil, high pressure) or pneumatic (air, lower pressure) — this alone rules out several materials.

2. What's the operating temperature and fluid? Standard mineral oil at normal temperatures → NBR. High heat, synthetic fluids, or aggressive chemicals → FKM. Extreme cold or heat swings → VMQ.

3. Does it move, and which direction? A static wear ring needs FRPR. A piston that only pushes needs a single-acting seal; one that pushes and pulls under load needs double-acting.

Still unsure? Use the Size finder on the main store — enter your measurements and the right category will show itself, or add a note to your quote request and we'll confirm before dispatch.