Which vacuum gauge range do I need for a rotary vane pump?

A two-stage rotary vane pump reaches roughly 10 to the minus 3 millibar, so a Pirani or thermocouple gauge covering 1 to 10 to the minus 3 millibar is enough. Choose a Pirani-Penning combination when the same line also has to be read at high vacuum, because a thermal gauge becomes inaccurate below about 10 to the minus 3 millibar and a cold cathode or hot cathode sensor covers 10 to the minus 2 down to 10 to the minus 9 millibar.

Why does my gauge read a different pressure from another gauge on the same line?

Thermal gauges are gas dependent and are calibrated for nitrogen or air, so hydrogen, helium or solvent vapour will shift the reading by a factor of two or more; apply the gas correction factor or switch to a capacitance diaphragm gauge, which measures pressure directly and is gas independent. A second cause is location: a gauge close to the pump inlet reads lower than one at the far end of a long, narrow line.

How often should a laboratory vacuum gauge be calibrated?

Check the zero and atmosphere readings before each campaign and send the sensor for calibration annually, or every six months where it is used for release testing or regulated work. A thermal gauge that no longer reads zero at base pressure, or drifts when tapped, should be cleaned or replaced rather than adjusted.

Does JWRESEARCH supply vacuum gauges and controllers in Singapore?

Yes. JWRESEARCH supplies Pirani, thermocouple, capacitance diaphragm and Pirani-Penning combination gauges, single and multi-channel controllers, setpoint relays, sensors, cables, centring rings and KF and CF fittings, delivered across Singapore with selection advice for rotary vane, diaphragm, scroll and turbomolecular pump systems.

Vacuum Gauges and Controllers Singapore

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

A vacuum system without a gauge is operated by guesswork. The pump sounds right, the flask holds, and nobody notices that the line has been sitting at 20 mbar for a week because a joint sleeve has hardened. A gauge turns that into a number, and a controller turns the number into an action — switching a pump, closing a valve, or tripping an alarm before a sample is ruined.

At JW RESEARCH SUPPLY, we supply Pirani, thermocouple, capacitance diaphragm and combination vacuum gauges, controllers, sensors and the KF and CF fittings that connect them, to chemistry, pharmaceutical, semiconductor, materials and teaching laboratories across Singapore. This guide covers the ranges, the gas correction problem, and the installation details that decide whether a reading can be trusted.

Measuring Vacuum: Four Working Ranges

Vacuum is not one measurement. Rough vacuum from atmosphere to about 1 mbar, fine vacuum to 10⁻³ mbar, high vacuum to 10⁻⁷ mbar and ultra-high vacuum below that each need a different physical principle, which is why gauge selection starts with the range rather than the brand.

Gauge Type	Measuring Range	Gas Dependent	Typical Use
Thermocouple gauge	1000 – 10⁻³ mbar	Yes	Rotary vane pump monitoring, budget rough vacuum
Pirani gauge	1000 – 10⁻³ mbar	Yes	General rough and fine vacuum, stable and repeatable
Capacitance diaphragm gauge	1000 – 10⁻⁵ mbar (by model)	No	Process control, solvent vapour, corrosive gases
Cold cathode (Penning) gauge	10⁻² – 10⁻⁹ mbar	Yes	High vacuum, turbomolecular pump backing
Hot cathode (ion) gauge	10⁻¹ – 10⁻¹⁰ mbar	Yes	UHV, coating and surface science
Pirani–Penning combination	1000 – 10⁻⁹ mbar	Yes	One display from atmosphere to high vacuum

Specification Reference

Parameter	Typical Value	What It Affects
Sensor material	Stainless steel 304 / 316L, ceramic	Corrosion resistance to solvent and acid vapour
Flange / fitting	KF16, KF25, KF40, CF35, CF63, 1/8 in NPT	Fitting the chamber, line or pump inlet
Accuracy	±10 – 30% of reading (thermal), ±0.2% FS (capacitive)	Whether the number can be used for release decisions
Resolution	0.1% of range, 3 or 4 digit display	Seeing small leaks and slow pump-down trends
Output signal	0 – 10 V, 4 – 20 mA, RS485	Logging to a PC, PLC or chart recorder
Setpoint relays	1 – 3, adjustable hysteresis	Pump switching, valve interlocks, alarms
Max pressure at sensor	1 – 2 bar absolute (thermal sensors)	Surviving a vent or a rushed backfill
Operating temperature	5 – 50 °C sensor, electronics cooler	Stability in a Singapore plant room
Bakeout temperature	80 – 150 °C (UHV sensors)	Reaching base pressure after cleaning

Gas Correction and Mounting

Thermal gauges infer pressure from how quickly a heated wire loses heat, so the gas composition matters. Readings are normally calibrated for nitrogen or air. Hydrogen and helium conduct heat better and read high; argon and solvent vapour read low. For a line pumping dichloromethane or ammonia, either apply the correction factor from the sensor manual or fit a capacitance diaphragm gauge, which deflects a membrane and measures pressure directly, independent of gas.

Mounting decides accuracy as much as the sensor does. Place the gauge where it sees the chamber, not a dead leg or a pocket that traps condensate. Keep it away from the pump inlet if the number is meant to describe the experiment, and fit a centring ring and a fresh O-ring on every KF joint. A gauge that is loose by half a turn will read the leak it created.

Controllers, Setpoints and Interlocks

A controller adds two useful things: a display in the room and a decision. A single-channel unit with one setpoint can start a backing pump when pressure rises above a threshold, or trip a solenoid valve to isolate a flask. Multi-channel units show Pirani and Penning sensors side by side with automatic range crossover, so a single display runs from atmosphere to 10⁻⁹ mbar without an operator changing scales.

Set hysteresis wide enough that the relay does not chatter around the threshold, and test the interlock with the chamber empty before trusting it with a sample. Where a gauge protects a turbomolecular pump, wire the setpoint to the pump controller rather than relying on a person watching a display.

Calibration and Maintenance

Check zero at base pressure and the atmosphere reading before each campaign. Thermal sensors foul with oil mist and solvent residue, which shifts the reading; clean the tube with a suitable solvent, dry it fully, and re-check. Capacitive sensors should be zeroed at vacuum with the isolation valve closed. Send sensors for calibration annually, or every six months for regulated or release-testing work.

Store spare O-rings, centring rings and one spare sensor per critical system. A gauge that fails during a run costs more in lost sample than in hardware, and a two-minute swap is the difference between a rework and a report.

Frequently Asked Questions

Can one gauge cover atmosphere to high vacuum?
Yes, with a Pirani–Penning combination sensor, which switches between a thermal and a cold cathode element and gives one continuous display across the whole range.

Why does the reading drift after a solvent run?
Solvent has condensed on the sensor tube and is evaporating slowly, or the tube is coated. Clean and dry the sensor, then re-zero; if the drift persists, replace it.

Is a display gauge enough, or do I need a controller?
A display is enough for monitoring. Choose a controller when pressure has to trigger a pump, valve or alarm without an operator present.

Does JWRESEARCH supply vacuum gauges in Singapore?
Yes — Pirani, thermocouple, capacitive diaphragm and combination gauges, controllers, sensors, cables and KF and CF fittings, 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