Internal calibrated leak on an ASM detector: how often does it need recertifying, and can I keep using an expired one?

Once a year is the normal recertification interval, and the reason is physical rather than bureaucratic: a permeation-type calibrated leak empties. The helium reservoir loses gas continuously through the permeable membrane that defines its rate, so the rate itself drifts downward over the leak's life. An expired leak does not read wrong in a random direction — it reads low, and that makes your instrument look more sensitive than it is.

That is the part worth understanding before deciding whether to keep using one. Calibrating against a leak that has drifted low tells the instrument that a small signal means a large leak; you then pass parts that should have failed. If you are leak-testing to a customer specification, an out-of-date certificate is usually the thing an auditor finds first.

For Pfeiffer / Adixen ASM instruments the internal leaks are 109240 (200 cc) and 109241 (50 cc) — the number refers to the reservoir size, and the larger reservoir holds its rate longer. Both carry a certificate with a measured rate and a temperature coefficient; the rate is only valid at the stated temperature, which is why a leak used in an unheated workshop in winter reads differently from the same leak in summer.

What we see: instruments sent in for sensitivity problems where the leak, not the analyser, is the fault. The tell is simple — if a machine calibrates fine against an external leak but not against its internal one, the internal one is the suspect. That check costs nothing and we ask about it before quoting anything on the analyser side.

Send the instrument model and the leak part number from the label, plus the certificate date and the rate printed on it. We supply new calibrated leaks with certificates and we also handle recertification; for a leak more than a few years old, replacement is usually cheaper than recertifying a reservoir that is nearly empty, and we will tell you which case you are in.