Hydraulic Cylinder Tube

Hydraulic cylinder tube is the precision steel tube used to make the barrel of a hydraulic cylinder. It is specified by inside diameter, wall thickness, steel grade and surface finish, because the bore becomes the sliding surface of the piston seal. We supply it cold drawn in grades such as 20#, 45#, 27SiMn, 16Mn, 25Mn and St52, from 15 mm to 100 mm bore, either in the as-drawn condition or honed to Ra 0.2–0.4 µm, cut to the length your cylinder shop needs. Dimensional and tolerance requirements can follow EN 10305-4 or DIN 2391 when the drawing calls for them.

Price: quoted per specification. Steel prices move with the raw material market, so every quotation is confirmed at the time of order.

Hydraulic tube, hydraulic piping or cylinder tube?

Three names cover two different parts of the same system, and mixing them up is the most common reason a quotation comes back with the wrong tolerance. A cylinder tube is the barrel: its bore becomes the sliding surface, so it is bought by inside diameter and inspected on the bore. Hydraulic tube, or hydraulic piping, is the line between the pump, the valve block and the cylinder: it is bought by outside diameter and wall, and it has to bend and take fittings.

We draw both, but they are not inspected the same way. A barrel is measured on the bore at both ends and in the middle, and the roughness is recorded; a line is measured on OD and wall, and what matters is that it bends without flattening and takes a fitting without splitting.

Line sizes in inches and millimetres

Line tube is often ordered in inches while the barrel next to it is ordered in millimetres, which is why a single assembly can carry two size systems. The figures below are outside diameters: if a drawing says 3/8 hydraulic tubing, it means 9.53 mm OD, not a 3/8 bore.

The smallest cylinder bore we draw is 15 mm, so anything below that is line tube rather than barrel tube. Where a customer needs a small bore and a small line in the same order, both are quoted from the same workshop and shipped together.

What makes a cylinder tube different from a standard tube

A standard seamless tube is judged on OD, wall and grade. A cylinder tube is judged on the bore. Three things decide whether it works in a cylinder:

• Inside diameter tolerance. The bore is normally held to H8 or H9. A bore that is 0.05 mm oversize changes the seal clearance and the cylinder will drift or leak.
• Surface roughness. Honed bores are supplied at Ra 0.2–0.4 µm. Longitudinal marks left by drawing will wear the seal even when the diameter is correct.
• Wall thickness and eccentricity. The wall carries the pressure, and an eccentric wall produces an uneven chrome layer after plating and a weak side in the barrel.

That is why cylinder tube is bought to a standard such as EN 10305-4 rather than to a generic tube specification.

Two supply conditions

SRB (skived and roller burnished) produces a work-hardened, mirror-like bore in one pass and is the usual choice for high-volume cylinder production. Honing removes more material and is preferred where the bore must be corrected after heat treatment or where a specific cross-hatch finish is required.

Both routes are available: honing for corrected or small-batch work, and SRB for production runs.

If you machine the bore yourself, buy the cold drawn condition and leave 0.3–0.5 mm on the ID. If you assemble directly, buy the honed condition.

Pneumatic and air cylinder tube

An air cylinder barrel is specified the same way as a hydraulic one, on the bore and the surface finish, but the pressure is lower and the wall can be thinner. We supply steel barrel tube from 15 mm to 100 mm bore, cold drawn or honed to Ra 0.2-0.4 µm, for pneumatic cylinders, automation actuators and air springs. Where the design calls for aluminium, the bore tolerance and roughness are the same, and the honing is done in the same shop.

The one difference worth flagging at quotation stage is lubrication. An air cylinder that runs dry needs a smoother, more consistent bore than one that is oiled through the air line, so the finish is agreed before the tube is honed rather than after.

Specifications

Every size is made to drawing. Send the ID, wall and length and we will confirm the nearest available tube.

Steel grades

20# is the default for general-purpose cylinders. 27SiMn is the usual choice for high-pressure barrels because it reaches the required strength with a thinner wall, and 45# is common where the barrel is machined and the bore is finished after welding. 16Mn covers drawings written for E355 or St52-3, and St52 is still quoted on older DIN drawings. Other grades can be discussed against the drawing. Mill certificates are supplied with every lot.

Quality control

Every batch is checked at four points before packing:

• Chemistry and grade — mill certificate matched to the heat number.
• Dimensions — ID and OD measured at both ends and at mid-length; wall thickness checked at four points around the circumference.
• Bore finish — roughness tester on three positions along the bore; visual check for longitudinal scoring under oblique light.
• Length and end finish — measured against the order, with ends checked for burrs and chamfer.

Inspection records are kept against the order number and can be issued with the shipping documents.

Products

Hydraulic cylinder tube is used in:

• Welded and tie-rod hydraulic cylinders
• Forklift and aerial platform cylinders
• Excavator, loader and agricultural implement cylinders
• Shock absorbers and suspension struts
• Presses, injection moulding machines and machine tools

Hydraulic oil is the working medium, but the tube also sees water-glycol and, in marine and offshore use, salt spray on the outside. For those cases we can supply the OD painted or plated.

What to send with an enquiry

To quote accurately we need:

• Inside diameter and outside diameter, or the drawing
• Wall thickness, if fixed
• Length per piece and total quantity
• Steel grade, or the working pressure if the grade is open
• Bore condition: as drawn or honed
• End finish: plain, chamfered, threaded
• Surface treatment: oiled, painted, zinc plated

Send these and we will reply with price, lead time and the nearest standard size.

FAQ

What is the difference between a honed tube and a skived tube? Skiving removes material with a cutting tool, then a roller burnishes the surface. Honing uses abrasive stones on a rotating head. Both can reach Ra 0.2–0.4 µm; skiving is faster and work-hardens the bore, honing gives better control when the bore has to be corrected.

Which grade should I choose? Use 20# for general-purpose cylinders and 16Mn where the drawing calls for E355 or St52-3. For high-pressure barrels, 27SiMn gives the highest yield strength and allows a thinner wall. 45# is used where the barrel is machined after welding, and St52 where the drawing is still written to DIN 2391. Other grades can be quoted on request.

What ID tolerance can you hold? H8 and H9 as standard. Tighter tolerances are possible after honing, but they are agreed per size because they depend on the wall and length.

Do you supply cut to length? Yes. Tubes are cut to the length on the order, deburred, and oiled before packing. Cut length tolerance is ±1 mm unless the drawing says otherwise.

Do you issue certificates? Yes — mill certificate, dimensional report and roughness report. 3.1 certificates to EN 10204 are issued on request.