Hose perforation: why the outer cover is pin-pricked
For gas service the hose cover is deliberately punctured with thousands of micro-holes — otherwise gas that has permeated through the inner tube accumulates under it and blisters the hose. We look at the physics, when perforation is mandatory and when harmful — and how it is done on the manual LT-ZK machines.
Rubber and thermoplastic look airtight, but for gases this is not quite true: under pressure, gas molecules slowly diffuse through the hose's inner tube. For liquids the effect is negligible, but on nitrogen, compressed air or CO₂ it works constantly. The gas that has passed through moves freely through the reinforcement — braid and spiral are not airtight — and stops at the outer cover, which is almost impermeable to it. What happens next is exactly what perforation exists for.
What happens without perforation
Gas accumulates in the space between the reinforcement and the cover. At first it shows as local blisters on the hose surface. Then the cover delaminates from the reinforcement over a growing area. The worst scenario is a rapid release of working pressure: the accumulated gas, and the gas dissolved in the rubber, expands sharply and balloons the cover up to rupture. With flammable gases there is a second risk: the leak does not vent evenly but accumulates and escapes in a burst.
Perforation removes the problem at the root: the outer layer is punctured with an even grid of micro-holes down to the reinforcement. The gas vents continuously in small portions — there is simply nowhere for it to accumulate. Hose strength is unaffected: the pressure is carried by the reinforcement, and it is not touched.
When perforation is mandatory — and when harmful
Mandatory — for gas service where the hose manufacturer requires it: nitrogen lines (including accumulator charging), high-pressure compressed air, CO₂ and other gases. This particularly concerns thermoplastic hoses: in catalogues the requirement is marked as a perforated or pin-pricked cover. The exact criterion is always the same — the hose manufacturer's documentation for the specific medium and pressure.
Not needed and undesirable — for ordinary liquid hydraulics: a punctured cover opens a path for moisture to the steel reinforcement and accelerates corrosion. So covers are perforated not "just in case" but strictly where the medium is a gas.
How it is done: the LT-ZK series
The manual LT-ZK machines roll the hose through a perforating tool: the needles pass through the outer layer to a limited depth — down to the reinforcement, without touching the wire — leaving an even grid of punctures along the whole length and circumference. The drive is manual, no power is needed, and the tool is included in the delivery.
| Model | Working range | Dimensions | Weight |
|---|---|---|---|
| LT-ZK100 | 8–45 mm | 290×150×330 mm | 8 kg |
| LT-ZK200 | 5–60 mm | 270×200×400 mm | 22 kg |
| LT-ZK300 | 30–100 mm | 400×265×565 mm | 58 kg |
The core model of the range is the LT-ZK200 with a 5–60 mm range: it covers practically the whole hose range of a service centre. The ZK100 is the compact version for mobile work, the ZK300 handles industrial hoses up to 100 mm OD. In the shop process chain perforation is done on the finished assembly or the cut hose — before or after crimping, per the hose manufacturer's instructions; the hose types themselves are covered in the hose guide.