Which ion source filament does my helium leak detector take?

Find your detector in the table below and read off the part number. The ion source filament is the electron emitter of the mass-spectrometer cell: it is heated until it emits, those electrons ionise the gas drawn in from the test port, and only the helium ions that result reach the collector and become the leak signal. Every helium leak detector has one, and on every one of them it is a consumable.

What surprises most buyers is how few distinct filaments sit behind all those brand names. The part carried as 16504 fits the entire INFICON UL series, the LDS3000 and LDS800, Leybold's Phoenix L200i and L300i and the UL500, and the LINXON LX218. The part carried as B8199999EU fits both the Pfeiffer HLT series and the Edwards ELD500. If you service mixed equipment, one spare frequently covers two machines from two manufacturers.

Two things end a filament's life. The emitting surface evaporates slowly over running hours — that shows up as a calibration factor climbing month after month. And it oxidises suddenly when air reaches it hot: a burst test piece, a hose pulled off while the detector is still in test mode, a roughing pump that loses seal. The first is gradual, the second kills it in a single event.

The diagnostic is the same on every brand. If the detector reaches its normal test pressure and the gauge readings look sensible, but the helium signal is flat or calibration will not complete, the filament is the suspect. If the machine cannot reach test pressure at all, the fault is upstream — roughing pump, turbo, or a leak in the detector's own manifold — and a new filament will not fix it.

Most analyser cells hold two filaments with automatic switchover. That is a safety net and a trap at once: a detector running on its standby filament looks perfectly healthy right up until the second one goes, and then it stops mid-shift. Check which one yours is on before you decide how many to order.

Material matters more than it looks. Plain tungsten is cheap and common in gauge filaments, but it oxidises instantly if air reaches it hot. Iridium — and yttria- or thoria-coated iridium — survives that and emits usefully at a much lower temperature, which is why nearly every modern leak detector uses it. The coating is the part that wears, and it is also the part fingerprints destroy: handle a new filament with clean gloves only, never wipe the emitting surface, and recalibrate against a calibrated leak after fitting, because a filament change always shifts sensitivity.

Send us the detector brand, model and serial number if you have it, plus whichever part number you are holding, and we will confirm the match before you order. Genuine and compatible grades are both available for most of these and we label which is which. Where a filament assembly is no longer manufactured at all, the original can often be re-welded with new filament wire, provided the mount, ceramic and feedthroughs are undamaged.