Cold Traps and Vacuum Manifolds Singapore
Every vacuum system in a working laboratory has two problems that are rarely written on the purchase order: what happens to the vapour the pump is pulling, and how several experiments share one pump without contaminating each other. A cold trap answers the first, a manifold answers the second, and the two are almost always specified together.
At JW RESEARCH SUPPLY, we supply cold traps, vacuum manifolds, stopcocks, gauges, KF and GL fittings and vacuum tubing to chemistry, pharmaceutical, materials, environmental and teaching laboratories across Singapore. This guide covers how traps work, how to size capacity, and how to lay out a manifold that stays leak-tight and readable.
What a Cold Trap Does
A cold trap is a glass vessel held at low temperature between the experiment and the pump. Condensable vapour meets a cold surface, drops below its dew point and freezes or liquefies there instead of reaching the pump oil or the high-vacuum stage. The pump oil stays clean, the achievable pressure improves, and the solvent is recovered rather than vented.
Position matters more than people expect. The trap must sit below the vessel it protects and close to the pump inlet, so liquid drains toward the trap and the tube run holding vapour stays short.
Trap Types and Coolants
| Trap Type | Coolant | Temperature | Typical Use |
|---|---|---|---|
| Round-bottom or finger trap | Dry ice + acetone / ethanol | approx. −78 °C | Rotary evaporation, solvent removal, general manifolds |
| U-shaped or coiled trap | Dry ice + acetone | approx. −78 °C | Schlenk lines, vacuum transfer, higher surface area |
| Finger trap, dewar cooled | Liquid nitrogen | approx. −196 °C | Argon, ethane, volatile ethers, high-vacuum protection |
| Solvent recovery trap | Dry ice or chilled water | −20 to −78 °C | Recovering wash solvents from vacuum concentrators |
| Cold trap with stopcock | Dry ice or liquid nitrogen | −78 to −196 °C | Isolating and removing the trap without breaking vacuum |
Specification Reference
| Parameter | Typical Value | What It Affects |
|---|---|---|
| Body material | Borosilicate glass 3.3 | Thermal shock resistance at −196 °C |
| Nominal capacity | 50 – 1000 mL | How much condensate one run can hold |
| Usable capacity | About 40 – 50% of nominal | Safe working volume before carry-over |
| Joint size | GL14, GL18, GL32, 24/29, 29/32, KF25, KF40 | Fitting the manifold and pump inlet |
| Working pressure | Atmospheric down to 10⁻³ mbar | Compatibility with the pump stage |
| Stopcock | PTFE plug, 2 mm or 4 mm bore | Sealing and conductance when open |
| Coolant dewar | 1 – 5 L, unclad or vacuum insulated | Hold time and refill frequency |
| Hold time, dry ice | 4 – 10 h depending on dewar | Whether an overnight run is safe unattended |
Sizing Trap Capacity
Work from the mass of vapour, not from the flask size. If a rotary evaporation run removes 400 mL of dichloromethane, the trap has to hold that volume as liquid or solid, and filling should stay under about half of nominal capacity. Frozen solvent expands and can crack a trap filled too full, and a trap that carries over dumps its contents into the pump oil in seconds.
For long unattended runs, use a larger trap or two traps in series, with the colder one second: the first takes the bulk load, the second polishes the stream before the pump.
Manifold Configurations
A vacuum manifold distributes one pump across several ports. The common forms are a straight glass or PTFE-coated tube with stopcocks, a double-bank Schlenk line with vacuum and inert gas rails, and a compact stainless rail with KF flanges for rough vacuum work.
Three details separate a manifold that works from one that leaks. Every port needs its own stopcock, so one flask can be isolated without disturbing the line. The bore of the stopcock and manifold tube sets the conductance: a 2 mm bore plug on a 10 mm rail chokes the pump. And gauges belong at the far end from the pump, where they read what the experiment actually sees.
- Ports: 3, 4, 6 or 8, with PTFE or glass stopcocks.
- Rail bore: 8 – 12 mm for rough vacuum, larger where speed matters.
- Sealing: PTFE sleeves or greased ground joints; grease-free where solvent attack is a concern.
- Gauges: a Pirani or diaphragm gauge for rough vacuum, a Pirani–Penning combination for two-stage work.
- Support: clamp the rail at two points; a loaded manifold should never hang from one joint.
Safe Operation and Maintenance
Never seal a filled trap and let it warm: pressure builds and the glass fails. Vent the trap before removing it, thaw it in a fume hood or warm water bath, and dispose of the recovered solvent as chemical waste. Wear cryogenic gloves and a face shield when handling liquid nitrogen, and fill dewars slowly to avoid boil-over.
Between runs, dry the trap fully — residual water freezes, blocks the inlet path and produces the slow pump-down people blame on the pump. Inspect stopcock plugs and joint sleeves for scoring, replace PTFE sleeves that no longer seal by hand, and leak-check the manifold by isolating it under vacuum and watching the gauge for a minute.
Frequently Asked Questions
Can I run a cold trap without a coolant?
No. An unfilled trap adds dead volume without condensing anything; it only helps as a knock-out pot for aerosols.
How often should the coolant be topped up?
Check every few hours. Dry ice in an unclad dewar can be gone in four to six hours, which is why overnight runs need an insulated dewar or a second trap.
Is a glass or a stainless manifold better?
Glass is visible and inert, which suits chemistry; stainless with KF fittings is tougher and faster to assemble for rough vacuum and filtration work.
Does JWRESEARCH supply cold traps in Singapore?
Yes — dry ice and liquid nitrogen traps, manifolds, stopcocks, gauges, KF and GL fittings and tubing, 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