Materials for hydraulic cylinders: which tube and which rod for which part
Each part of a hydraulic cylinder has its own requirement. Here is what decides the choice for the barrel, rod, piston and bushings, which product group to open, and when not. Sizes are on the product pages.
At a glance
A hydraulic cylinder is built from parts with different requirements: barrel, rod, piston, bushings and the oil line. This page shows which product group to open for each part; sizes, tolerances and grades are on the product pages.
- Barrel
- Precision steel tubes or a tube with a chrome-plated bore
- Rod
- Chrome-plated bars
- Piston and telescopic stages
- Externally chrome-plated tubes
- Bushings and blocks
- Continuous cast iron
- Oil line
- HPL tubes
What decides the choice for each part
Start from the part. For each one the table says what decides the choice, which group it belongs to, and when that group is the wrong one.
| Part | What decides the choice | Group | When not |
|---|---|---|---|
| Barrel | The tolerance and surface of the bore: the piston and seals work on it | Precision steel tubes; for a chrome-plated bore: internally chrome-plated tubes | HPL tubes are for pressure lines, not for the barrel |
| Rod | The outer surface: the rod leaves the cylinder and passes through the rod seal | Chrome-plated bars | A peeled bar has no chrome layer; the product data also lists it as a base for chrome plating |
| Piston, telescopic stages | A chrome-plated outer surface; for heavy duty also a hardened layer under the chrome | Externally chrome-plated tubes; for heavy duty induction-hardened chrome-plated tubes | If the chrome must be in the bore, see the internally chrome-plated tubes |
| Bushings, hydraulic blocks | The part is machined from solid stock | Continuous cast iron | If the part must be steel: calibrated round bars |
| Oil line to the cylinder | A tube for a pressure line in a hydraulic system | HPL tubes | Not a tube for a cylinder barrel |
Why the bore and rod are ordered with a tolerance class
The piston and rod seals work in the gap between the moving parts. The bore and rod tolerances set how large that gap can become, which is why seal makers specify them in their catalogues.
Seal housing dimensions are set in ISO 5597, and for elastomer-energized, plastic-faced rod seals in ISO 7425-2. These standards do not define the seal itself or the bore surface.
The tolerance class depends on the diameter and the seal. SKF, for example, gives f8 and H9 up to Ø120 mm and f7 and H8 above Ø120 mm for O-ring housings. What H8 and H9 mean is explained on the EN 10305 page.
Is there a tube for your bore
ISO 3320 sets a metric series of bore and rod diameters for hydraulic and pneumatic cylinders. The standard covers the cylinder's dimensions, not the tube.
The table shows the preferred bores in the series and whether the catalogue has a seamless H8 or welded H9 tube with that inside diameter.
| ISO 3320 bore | Seamless H8 | Welded H9 |
|---|---|---|
| Ø20 mm | No | Yes |
| Ø25 mm | No | Yes |
| Ø32 mm | No | Yes |
| Ø40 mm | No | Yes |
| Ø50 mm | Yes | Yes |
| Ø60 mm | Yes | Yes |
| Ø63 mm | Yes | Yes |
| Ø80 mm | Yes | Yes |
| Ø100 mm | Yes | Yes |
| Ø125 mm | Yes | No |
| Ø160 mm | Yes | No |
| Ø200 mm | No | No |
Three ordering mistakes
- Only “H8” or “H9”, with no standard or condition. H8 and H9 are ISO 286 classes, not EN 10305 designations. State both: the standard with grade and condition, and the bore tolerance.
- A line tube instead of a barrel tube. HPL tubes are for pressure lines; for a barrel, see the H8, H9 or HPZ precision tubes.
- No delivery condition. The seamless H8 tube is +SR and the welded H9 tube is +C, meaning no heat treatment after drawing. If you need another condition, put it in the enquiry.
A cylinder in a corrosive environment
When the rod or tube works in salty, humid or polluted surroundings, the choice is between hard chrome, nickel-chrome and a stainless base. The comparison is on a separate page.
Products for hydraulic cylinders
Sizes, tolerances and grades are on each product page.
Electric-welded cold-drawn precision H9 tubes
Cylinder barrel: an electric-welded precision tube.
→ View details
Catalogues and files
Questions about cylinder materials
Are the tube and rod made to ISO 3320?
No. ISO 3320 sets a series of bore and rod diameters for the cylinder, not the properties of the tube or rod. Tube inside diameters and rod diameters are on the product pages.
Where are cylinder tubes used?
Tube makers and stockists name earth-moving and construction machinery, cranes (including telescopic cylinders), energy, marine and offshore equipment, agricultural machinery and general engineering.
Send the cylinder parts and dimensions for a quotation.
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