How do you make a new tube for a hydraulic cylinder?
In a previous blog post, we explained how we cut open a cracked cylinder to preserve the other components. Now, we continue the repair process from the point where a new tube is being manufactured for the cylinder.
In our previous blog post, we explained how we opened a cracked cylinder by cutting it, allowing us to preserve the other components in good condition. Now we continue the repair process from the point where a new tube is manufactured for the cylinder.
The cylinder tube was measured in advance before disassembly, so the main dimensions for the new tube are already known. It’s a good idea to take plenty of photos of the cylinder before taking it apart—especially noting the positions of outlets, conduits, and connectors, all of which should be carefully measured.
Before machining the new tube, the other parts must be properly prepared. We start by machining the gland and end cap off. Manufacturing a new gland or end cap would be much more laborious compared to removing them, so we aim to reuse all parts that are still in good condition. This way, we can get the cylinder back to work quickly and keep the repair cost competitive compared to replacing the entire tube with a new spare.
During the removal stage, we also machine the chamfels / bevels onto the gland and end cap which must be dimensioned according to the cylinder’s size so that the weld can handle the stresses the cylinder will be subjected to.
After this, we manufacture the tube from materials that match the original. When machining the new tube, it’s important to account for the required profiles for the gland and end cap, as well as the thickness of the weld bevels.
We begin welding by attaching the gland to the tube. It’s especially important during both welding and machining that the gland is perfectly aligned. Even small deviations can cause issues in long-stroke cylinders, such as the rod or piston binding—often leading to damage inside the cylinder tube, typically near the end cap.
Once the gland is welded, the tube is sent for machining—or directly for honing. In this case, the tube first goes to the lathe, where the weld seams are machined, and honing is done after the end cap is welded in place.
Next, we weld the end cap in place. During end cap welding, it’s important to ensure that all holes and alignment lines remain straight.
After welding and grinding the weld seams, the cylinder tube moves on to honing. The heat generated during gland welding often causes slight deformations in the tube, so the gland area is honed to correct any distortion—ensuring, for example, that the gland isn’t oval or overly tight.
Once honing is complete, the tube is ready for final assembly with the other components. The cylinder’s function is verified during pressure testing, where we check the integrity of the welds and confirm that the rod moves freely throughout its stroke.
