Pneumatic Shaft Pressure: Find the Leak First A pneumatic shaft holds the roll with air pressure. Why the leak stays invisible until the winding is spoilt, and the two hard limits of a 0-500 kPa sensor.

What a pneumatic shaft actually does

A pneumatic (expandable) shaft grips a roll or a core by inflating a bladder or a set of pistons inside it. Air pressure is the only thing holding the load. While the pressure is where it should be, nothing about the shaft looks wrong: the roll turns true, the web tracks straight, the machine runs. When the pressure drops, nothing looks wrong either. That is the whole problem.

On a printing press or a slitter, a slow leak in the shaft circuit does not stop the machine. It changes the grip. The core starts to slip a little, the winding tension drifts, and the defect shows up several metres of material later — or on the next shift, when someone inspects the roll. By then the cost is not one sensor. It is material, machine time and a re-run.

Why the leak stays invisible

Three reasons, and they are all about where the gauge is:

• The gauge is on the supply line, not on the shaft. A manifold pressure of 7 bar tells

you nothing about the bladder of the third shaft on the machine.

• Couplings, seals and rotary unions leak quietly. In a press room, nobody hears it.
• Checking is a task, not a habit. Walking to each shaft with a gauge takes longer than

the check itself, so it gets skipped until something fails.

What a phone-readable sensor can do

Our BLE sensor is a small battery-powered pressure transmitter on the measurement branch: 2.4 GHz, no receiver, no wiring to the machine, read on a phone. Range 0-500 kPa gauge, ±2 kPa, IP67, CR1632 cell good for about 1.5 years and replaceable without re-pairing. A technician walks the line once a shift and reads each shaft: fifteen seconds per machine. The value can be recorded and forwarded, which turns "I looked at it" into an inspection record.

That is the honest scope: periodic verification, not continuous protection. Without a receiver there is no in-cabinet alarm and no live trend.

Two hard limits, said first

The 0-500 kPa range. A typical pneumatic shaft runs at 7 bar (about 700 kPa), which is above our standard range. For the shaft bladder you need a different sensor, not the catalogue part. We say this before the quotation, not after.

Steel blocks radio. A shaft is a closed steel body. 2.4 GHz does not pass through it. So the first engineering question is not "what pressure" but "where is the measurement point" — shaft end, an external port, a separate test line. If the only possible point is inside the shaft body, this is a custom project, not a catalogue product.

What we do not claim

We do not measure tension, we do not control the shaft, and we do not replace your maintenance plan. What we do is make the pressure visible on a routine walk-around, so a leak is found in days rather than at the end of a rejected roll.