What a cylinder barrel is and why buyers outsource it
A hydraulic cylinder barrel is the pressure-containing tube that houses the piston in a linear actuator. In contract manufacturing it is almost always supplied as a made-to-drawing welded and machined fabrication: a rolled or flat-plate shell with a longitudinal seam, welded end caps or flanges, and machined faces for ports, mounts and rod glands. Buyers who run equipment such as presses, lifts, construction machinery and material handling systems often outsource the barrel rather than hold the welding, machining and inspection capacity in house.
Realjet supplies welded and machined machinery components to customer drawings. A cylinder barrel is one example of that work. The buyer owns the design and the performance intent; the supplier delivers the fabricated and machined part to the stated tolerance and traceability. Finishing steps such as bore honing, rod plating and hydrostatic certification are project specific and need to be confirmed in the order scope.
Drawing and specification inputs to prepare
Before requesting a quote, prepare a package that lets the supplier plan welding, machining and inspection without guesswork. At minimum this includes:
- The barrel outline and section drawing with all machined dimensions called out, not just a 3D model.
- Material grade for the shell and end components, with the relevant standard reference.
- Wall thickness and any taper or counterbore at the ends.
- Bore diameter and the tolerance and surface finish required on the inside.
- Port positions, sizes and thread forms, plus any locating features.
- Mounting flange or trunnion geometry and the bolt circle.
A clear drawing prevents the most common source of rework: a machined feature that looks minor on paper but drives a different setup at the machine. Where the design is still open, state the function and let the supplier propose a fabrication route, then freeze the drawing before production.
Material, welding procedure and traceability
The shell is typically a structural or pressure-vessel grade steel plate or tube. Specify the grade and, where the part is pressure related, the applicable code or client specification. Material evidence matters: request mill certificates to EN 10204 3.1 as a baseline, and 3.2 where a third-party witness is required.
Welding should be defined by a written procedure. For structural and pressure parts this usually means a WPS and PQR to AWS D1.1 or an ISO 3834 qualified system, with the welding consumable and position stated. The buyer does not need to write the procedure, but should confirm which standard applies and what non-destructive testing is expected. Radiographic or ultrasonic examination of the longitudinal seam, and magnetic particle or dye penetrant checks at critical welds, are typical requirements that change both lead time and cost.
Machined interfaces and bore tolerance
The barrel is useless if the machined faces do not match the mating parts. Decide early which interfaces are machined and to what class. General machining tolerances can follow ISO 2768, but the bore, port seats and mounting faces usually need their own limits. Bore diameter and out-of-roundness are often the tightest requirements; ISO 4394 covers finished steel tube bores for cylinders and is a useful reference when the bore is supplied finished.
State the surface finish on the bore and any sealing faces, because that determines whether the supplier stops at turning or continues to honing. A turned bore may be enough for low-pressure or non-sealing applications, while a hydraulic sealing surface normally needs a finer finish that the supplier may handle in house or subcontract. Put that decision in the scope rather than leaving it implied.
Inspection, testing and scope boundaries
Separate what the supplier delivers from what the buyer or a third party performs. A useful split looks like this:
| Scope item | Usually supplied by the fabricator | Confirm per project |
|---|---|---|
| Shell welding and end welds | Yes | WPS and PQR standard |
| Machined faces and bore | Yes | Bore finish class |
| Material certificates | Yes | 3.1 or 3.2 |
| NDT of seams and welds | Yes | Method and acceptance level |
| Bore honing | Possible | In house or subcontracted |
| Hydrostatic pressure test | Possible | Test pressure and record |
| Rod, seals and chrome plating | No | Supplied by others |
This table is a planning aid, not a statement of capability. Realjet delivers the fabricated and machined barrel; whether honing, pressure testing or plating sit inside the order is a contract decision the buyer should state up front.
Lead time and logistics factors
Barrel length and diameter drive both the welding setup and the machining envelope. Long or large-bore barrels need a lathe or boring capacity that not every shop holds, and they ship as oversized or heavy freight. State the finished length, the maximum outside diameter and the packed weight early so the supplier can confirm it fits the machine and the export crate. For export, corrosion protection and the lifting points are part of the deliverable and should appear in the drawing or the packing specification.
How to approach a contract manufacturer
Start the conversation with the drawing and the few values that drive cost: bore size, wall thickness, material, weld class and the machined features. Ask the supplier to confirm the fabrication route, the inspection level and which finishing steps are inside the quote. A supplier that asks for the pressure class, the test requirement and the certification early is showing it understands the part.
Realjet's contract manufacturing page describes the welding, machining and assembly work performed to customer drawings. Use it to judge whether the shop's capacity matches your barrel, then send the drawing package and the inspection expectations together so the quote reflects the real scope.