What sensitivity do I need from a helium leak detector?

Match the detector to the acceptance criterion, not to the best number on the datasheet. A rotary vane vacuum system that must hold 10⁻² mbar overnight is adequately tested with a sensitivity of 1 × 10⁻⁸ mbar·L/s. Turbo-pumped systems, glove boxes and UHV chambers usually specify 1 × 10⁻¹⁰ mbar·L/s or better, which calls for a helium mass spectrometer with a hard vacuum inlet and a calibrated standard leak.

Can I use a helium leak detector on a pressurised system?

Yes, in sniffing mode. The chamber is filled with a helium mixture at a modest overpressure and the probe is moved slowly along welds, flanges and seals at about 10 mm per second, keeping the nozzle within 2 to 3 mm of the surface. Sniffing is less sensitive than vacuum mode, typically 1 × 10⁻⁷ mbar·L/s, but it locates the leak directly and works on assemblies that cannot be evacuated.

Why does my leak rate reading keep drifting?

Drift is normally background helium, not a changing leak. Helium accumulates in a closed, air-conditioned laboratory and lingers in clothing, hair and ceiling voids, so each spray raises the background for minutes. Ventilate the room, spray sparingly, wait for the signal to return to background between sprays, and keep the detector's own calibration leak closed except during the daily check.

Helium Leak Detectors and Leak Testing Singapore

Q: Does JWRESEARCH supply leak detection equipment in Singapore?

Yes. JWRESEARCH supplies helium mass spectrometer leak detectors, portable sniffing units, calibrated standard leaks, helium regulators and KF and CF inlet adapters, together with helium tracer gas and leak-test accessories, delivered across Singapore with advice on sensitivity targets and test procedures.

Published: {{NEW_ARTICLE_DATE}} | By JWRESEARCH | Category: Laboratory Equipment

A vacuum system that will not reach its base pressure is usually described as a pump problem. In practice the pump is often healthy and the chamber is leaking, and the only way to know is to measure. Leak testing turns a vague complaint about slow pump-down into a number with a location attached, which is what a maintenance decision needs.

At JW RESEARCH SUPPLY, we supply helium mass spectrometer leak detectors, portable sniffing units, calibrated standard leaks and the KF and CF inlet hardware that connects them to Singapore laboratory systems. This guide covers the main test methods, the sensitivity each one can actually deliver, and a procedure that gives repeatable results in a humid, air-conditioned building.

Comparing the Four Practical Methods

Every method trades sensitivity against convenience. Bubble testing finds a visible leak in a minute; helium testing finds a leak four orders of magnitude smaller and takes an afternoon of setting up.

Method	Typical Sensitivity (mbar·L/s)	Works On	Best For
Bubble / immersion test	1 × 10⁻³	Pressurised parts, small assemblies	Quick confirmation on glassware, tubing and fittings
Pressure decay	1 × 10⁻³ to 1 × 10⁻⁴	Sealed volumes with a pressure gauge	Routine QC on capped vials, filter housings, valve bodies
Helium sniffing	1 × 10⁻⁷	Pressurised systems, large chambers	Locating a leak on an assembly that cannot be evacuated
Helium vacuum mode (mass spectrometer)	1 × 10⁻⁹ to 1 × 10⁻¹²	Evacuated chambers, sealed devices	Acceptance testing, UHV, glove boxes, cryogenic vessels

Specification Reference

Parameter	Typical Value	What It Affects
Minimum detectable leak rate	1 × 10⁻⁹ to 5 × 10⁻¹² mbar·L/s	Whether the unit can certify a UHV or sealed-device specification
Inlet pressure (vacuum mode)	0.1 – 10 mbar at the test port	Whether the roughing pump can bring the chamber into range
Response time	0.5 – 3 s	Probe speed during sniffing and dwell time between sprays
Pumping speed at inlet	1 – 30 m³/h	How quickly background helium clears between measurements
Mass range / resolution	Fixed mass 4 (helium); some units mass 2, 3, 4	Rejecting hydrogen and argon interference in sniffing mode
Inlet flange options	KF 16 / 25 / 40, CF 35 / 63, 1/8 in Swagelok	Connecting to the chamber without adding a leak of your own
Calibrated leak (standard leak)	1 × 10⁻⁷ to 1 × 10⁻⁹ mbar·L/s, helium filled	Traceability of every reading and detection of drift
Operating temperature	5 – 40 °C	Stability in an air-conditioned plant room

Setting a Sensitivity Target

Start from the acceptance criterion in the specification, or derive one. A rough rule for a pumped system is that the total leak rate should be small enough that the leak cannot dominate the base pressure you require. For a chamber that must sit at 10⁻³ mbar with an inlet pumping speed of 10 m³/h, a leak in the 10⁻⁵ mbar·L/s range is already significant; for 10⁻⁶ mbar the target drops to 10⁻⁷ mbar·L/s and only helium vacuum testing can verify it.

A detector running at 10⁻¹¹ mbar·L/s picks up helium permeating through elastomer O-rings and desorbing from chamber walls, so the test never returns to zero and the operator spends the day chasing a "leak" that is background physics. Choose the least sensitive instrument that meets the criterion.

Running a Repeatable Test

Rough the chamber down until the inlet pressure is inside the detector's operating range; most units refuse to analyse above about 10 mbar and will trip an inlet protection valve. Then let the reading settle to a stable background — typically two to five minutes on a small system — and record it. That background is your floor for the session.

Spray helium in short bursts, from the top of the assembly downwards, because helium is lighter than air and rises. Work weld by weld and flange by flange, and pause between sprays long enough for the signal to return to background. If the signal stays elevated after a spray, the leak is real and you have found its neighbourhood; if it decays in seconds, you sprayed too much and are reading a cloud.

Finish with a calibrated standard leak. A reading that cannot be reproduced against a known leak is not a measurement, and a detector whose sensitivity has drifted will pass a chamber that should have failed.

Practical Notes for Singapore Sites

High ambient humidity matters more than most guides admit. Water vapour on cold traps and in roughing lines loads the detector's own pump, lengthens the time to reach background and can trip a cold-trap interlock. Fit a cold trap or a dry inlet filter, and empty it before each session rather than after.

Keep a dedicated set of blanking flanges and new centring rings for testing. A used O-ring that has taken a set will leak at the test port and the operator will spend an hour testing the chamber instead of the fitting.

Frequently Asked Questions

How long does a leak test take?
A single flange or weld set on a small chamber takes 10 to 20 minutes including evacuation and background stabilisation. A full multi-port system with documentation can take half a day.

Can I use nitrogen instead of helium?
For pressure decay, yes. For mass spectrometer detection, no: the instrument is tuned to mass 4, and helium's small molecule and low background are what make the sensitivity possible.

What counts as a pass?
Whatever the drawing or validation protocol states, measured against a calibrated leak and recorded with the test conditions. A pass without a documented sensitivity figure is an opinion.

Does JWRESEARCH supply leak detection equipment in Singapore?
Yes — helium mass spectrometer and sniffing detectors, calibrated standard leaks, helium regulators, KF and CF inlet adapters and leak-test accessories, delivered across Singapore.

Contact JWRESEARCH

JW RESEARCH SUPPLY — laboratory equipment and consumables, Singapore.
Tel / WhatsApp: +65 8039 3660
Email: SINGAPORE@JWSHY.COM
Website: www.jwresearch.cn