Articles / leaks

What a 3 mm leak really costs — and how to price a leak survey

2026-07-04 · by Cas, air-compressor-guide.com · every number below is a real simulation output

A 3 mm hole is a failed fitting, a worn quick-coupler, a cracked pushfit — something you will never hear over plant noise. On a completely average small plant, one of them costs €2,037 per year. Most plants have five to ten.

The setup

We simulated a deliberately ordinary system: a fixed-speed 6 m³/min screw compressor cycling between 6.0 and 7.0 bar, a 1 m³ receiver, 40 m of main line plus a 25 m drop, mixed steady and cyclic demand. Tariff €0.25/kWh, 6,000 running hours a year. Baseline energy: 20.9 kW average, €31,355/yr.

Then we dropped a single 3 mm leak on the distribution line and re-ran the simulation.

Assumptions: €0.25/kWh · 6,000 h/yr · leak at line pressure. Re-runs live in the demo with your tariff.

Why so much? The physics of a hole

Air escaping through a hole to atmosphere at plant pressures is choked flow: above roughly 1.9 bar absolute upstream, the air in the orifice throat reaches the speed of sound and the leak passes its maximum possible flow regardless of what's downstream. Practically, that means a leak's flow scales with your line pressure and the hole area — and it never takes a break. Nights, weekends, holidays: if the system is pressurized, the leak is working.

The compressor pays for it in duty cycle. In our simulation the machine's duty climbed from 50% to 56% — six extra percentage points of loaded running, every hour, to feed one hole.

The leak survey math

Once you know a 3 mm leak is worth ~€2,000/yr, leak survey economics get simple. An ultrasonic survey on a small plant typically finds several leaks in the 1–3 mm class. If a day of surveying plus a day of fixes recovers even three modest leaks, the payback is measured in weeks, not years. That's also how to price a survey if you're the consultant: the deliverable isn't "a list of hisses," it's a euro number per leak with a repair priority — exactly what a simulation gives you.

One caution in the other direction: leak fixing has diminishing returns, and the honest way to present it is leak-by-leak, not as a single inflated percentage. Model your actual found leaks and let each one carry its own number.

Check it on your own numbers

Your tariff isn't €0.25 and your hours aren't 6,000? The free leak cost calculator gives a first estimate from the choked-orifice physics — and the demo plant re-simulates the full system response with your inputs.