A distillation apparatus is a heated boiling vessel, a condenser, a receiving flask and, on most modern setups, a vacuum source, joined by ground-glass joints and clamps. We build ours as a matched line: assembly is less about learning part names than about sizing the bath, the condenser and the pump to each other.
What are the parts of a distillation apparatus?
Every distillation apparatus, from a teaching-lab glass train to a production solvent recovery line, is the same five jobs in sequence. Put heat in. Turn liquid to vapor. Route that vapor somewhere. Take the heat back out. Catch what condenses.
The parts map onto those jobs one for one:
- Boiling flask (still pot). Holds the mixture. Sits in or on the heat source.
- Heat source. A heating mantle, a hot plate, or on our units a temperature-controlled bath.
- Distillation head. The glass fitting on top of the boiling flask that takes the vapor sideways and holds the thermometer. On a classic three-neck train this is where the thermometer bulb sits level with the side arm, so you read the vapor temperature and not the liquid.
- Condenser. A jacketed tube with coolant flowing through the outer jacket. Vapor goes in warm, liquid comes out cool.
- Receiving flask (collecting flask). Catches the distillate.
- Vacuum source. Optional on a water still, near-mandatory on anything heat-sensitive, because dropping the pressure drops the boiling point.
- Clamps, stands and joints. The unglamorous half. This is where most assemblies actually fail.
That list is what a labelled diagram gives you, and it is where most articles on this topic stop. The problem is that a diagram has no scale. It draws the condenser and the pump the same size whether you are stripping a small bench sample or a 3 L batch, and that missing scale is the thing that goes wrong when people assemble a real setup for the first time.
How do you assemble a simple distillation apparatus?
Assembly order matters, and the rule is boring: build from the fixed point outward, and never force glass into position.
1. Set the heat source first. The bath or mantle is the heaviest, least movable part. On our benchtop units the bath is a fixed 260 x 150 mm well, so the flask position is decided before you touch any other component. Everything above it gets clamped to fit the bath, not the other way round.
2. Clamp the boiling flask. One clamp at the neck, snug, not crushed. The flask should hold its own position with the clamp loose enough that you could still rotate it a few degrees by hand.
3. Fit the distillation head or drive joint. This is the step where joint size stops being a footnote. Our RE-101 and RE-201D take a 24# ground joint on the rotary flask; the larger RE-301 uses a 50# flange port instead. Those are not interchangeable. If you order a 3 L flask expecting it to drop onto a 24# joint, nothing you do at the bench will make it fit, and no parts diagram will have warned you, because a diagram draws every joint the same.
4. Hang the condenser and connect coolant last-in, first-out. Coolant enters at the low end and leaves at the high end, so the jacket stays full. Reverse it and the jacket runs part-empty, condensing efficiency drops, and you will see vapor reaching the receiver.
5. Attach the receiving flask, then the vacuum line. Vacuum goes on last so you are not pulling on a joint you have not seated yet.
6. Leak-check before you heat. Pull vacuum on the cold assembly and watch the gauge settle. A joint that leaks cold will leak worse hot, once the grease thins.
On a rotary setup the same six steps collapse into three, because the head, the drive and the condenser arrive as one aligned assembly. That is most of the argument for a bench rotary evaporator with a 1 L or 3 L evaporating flask over a hand-built glass train: you are not aligning four independent clamps every time you change solvent. If you want the physics behind why the rotating film evaporates faster than a static pot, we covered that in how a rotary evaporator actually works.
What does an assembled apparatus look like in numbers?
Here is the part a labelled diagram cannot show you: the real numbers on a working, assembled line, and what each one constrains. These are the parameters from our own sheets, not a generic template.
| Assembly stage | Part | Spec on our sheets | What it constrains |
|---|---|---|---|
| Boil-up | Evaporating flask | 1 L (RE-101, RE-201D), 3 L (RE-301) | Batch size per run |
| Boil-up | Heated bath | 260 x 150 mm, 1000 W, room temperature to 200 C, plus or minus 1 C | How fast heat goes in, and whether a heat-sensitive product survives it |
| Joint | Flask-to-drive connection | 24# ground joint (RE-101, RE-201D); 50# flange port (RE-301) | Which flasks and adapters physically fit |
| Vapor path | Rotation | 40 W motor, 0-120 rpm | Film thickness and evaporation surface area |
| Condense | Glassware | GG3.3 borosilicate glass | Thermal shock tolerance and solvent compatibility |
| Collect | Collecting flask | 1 L on RE-101, RE-201D and RE-301 | Run time before you stop to drain |
| Pull vacuum | Rated vacuum at the apparatus | Up to -0.095 MPa | Boiling point depression, and therefore bath temperature |
| Utilities | Power supply | AC 220 V / 50 Hz | Bench circuit and plug type |
Read the table sideways rather than down and the sizing relationship appears. The 3 L flask on the RE-301 is three times the batch of the RE-101, but the bath is the same 260 x 150 mm well at the same 1000 W, and the collecting flask stays at 1 L on all three models. So scaling the boiling flask does not scale the rest of the apparatus. On a 3 L batch you are putting the same heat into three times the liquid, and you will fill that 1 L receiver before the run is done.
That is not a defect. It is the trade the design makes, and it tells you what to plan for: on the RE-301, expect a longer run and at least one drain stop. Nobody who publishes a labelled parts diagram will tell you that, because the diagram has no numbers in it.
How do you size the vacuum pump to the apparatus?
This is the assembly mistake we see most often, and it is invisible on a parts list. People buy the apparatus, then buy “a vacuum pump” as an afterthought, and match nothing.
The apparatus is rated to pull to -0.095 MPa. That is the number the flask, joints and condenser are built to hold. So the question for any vacuum source is whether it reaches that level, and whether it moves enough gas to get there in a sensible time while the bath is boiling solvent off.
Our SHZ-D(III) circulating water vacuum pump lists two flow numbers, and confusing them is where the sizing goes wrong:
| Model | SHZ-D(III) |
|---|---|
| Power | 180 W |
| Flow rate | 60 L/min |
| Single tap pumping speed | 10 L/min |
| Voltage | 220 V |
| Pump type | Water-ring circulating vacuum pump |
The 10 L/min figure is the one your apparatus actually gets. The 60 L/min headline belongs to the pump as a whole, not to the single tap your rotary evaporator is hooked to. Size a benchtop rotovap against 60 L/min and you have overestimated your vacuum source by a factor of six. Size it against 10 L/min and your expectations match the hardware.
Three consequences follow from that one distinction:
- Do not hang more benches off one pump than the taps support. Every tap in use is drawing from the same water ring. Two rotovaps on one pump is not two independent vacuum sources.
- Being a water-ring pump sets the floor. A circulating water pump pulls against the vapor pressure of its own working water. That is a real physical limit, and it is why the achievable vacuum is a property of the pump plus its water temperature, not a single catalogue number. Check the ultimate vacuum figure against the -0.095 MPa the apparatus is rated for before you assume they match.
- Solvent goes into that water. A water-ring pump on solvent duty is also a solvent trap you have to maintain. Plan the water change, not just the purchase.
The pump, the condenser and the cooling source are one decision, not three. We wrote a separate piece on matching a rotary evaporator to its vacuum pump and chiller that works through the whole chain. If your setup is a matched line rather than a single bench, a rotary evaporator system quoted as a complete evaporation line gets sized as one unit, with bath temperature, flask volume, condenser capacity, vacuum level and chiller support specified together.
How is a reflux apparatus different?
Same glass, opposite intent. A distillation apparatus routes vapor away from the pot and collects it somewhere else. A reflux apparatus condenses vapor and drops it straight back into the pot.
Mechanically the difference is one part: the condenser is mounted vertically over the boiling flask instead of angled toward a receiver, and there is no distillation head taking vapor sideways. That is it. Reflux is what you run when you want to hold a mixture at its boiling point for hours without losing volume, typically to drive a reaction.
So the assembly question is not “which apparatus”, it is “which way is the condenser pointing”. If you have a boiling flask, a condenser and clamps, you already own both configurations. What you do not automatically own is the distillation head and receiver adapter that turn reflux into distillation.
Which distillation kit do you actually need?
Three honest answers, depending on what you are doing.
A ground-glass kit, if you are teaching or running one-off separations. Cheap, flexible, and you learn the joints. Slow to assemble, easy to misalign, and you will spend more time clamping than distilling.
A benchtop rotary evaporator, if you strip solvent regularly. The head, drive and condenser come pre-aligned, so the assembly you do daily is one flask and one clip. Our 1 L and 3 L bench units run a 1000 W bath to 200 C with plus or minus 1 C control and hold up to -0.095 MPa, on a standard AC 220 V / 50 Hz outlet. If your batch never exceeds 1 L, skip the RE-301 and its 50# flange port; you are paying for a flask you will not fill and giving up the more common 24# joint.
A matched system, if solvent recovery is a process step and not a chore. Once the pump, chiller and condenser have to be sized against each other and against a target throughput, buy them as a line. Browse the full rotary evaporator range to see the configurations, and if your separation is heat-sensitive enough that even vacuum distillation degrades it, our molecular distillation equipment selection guide covers the short-path route instead.
Frequently asked questions
What are the essential parts of a simple distillation apparatus?
A boiling flask, a heat source, a distillation head holding the thermometer, a condenser with coolant, and a receiving flask. Add a vacuum source when the material is heat-sensitive, since reduced pressure lets you boil the solvent off at a lower bath temperature.
Which way does coolant flow through the condenser?
In at the low end, out at the high end. That keeps the jacket completely full against gravity. Connect it the other way and the jacket runs partly empty, condensing drops off, and vapor can reach your receiving flask uncondensed.
Do I need a vacuum pump for a lab distillation apparatus?
Not for water or high-boiling material at atmospheric pressure. You do need one for heat-sensitive product. Our rotary evaporators are rated to -0.095 MPa, and pulling that vacuum is what lets a 1000 W bath work well below the solvent’s atmospheric boiling point.
Why won’t my 3 L flask fit my rotary evaporator?
Almost certainly a joint mismatch. Our RE-101 and RE-201D use a 24# ground joint on the rotary flask, while the RE-301 uses a 50# flange port. Flask volume and joint type are two separate specs, and a bigger flask does not automatically mean a bigger joint.
Can two rotary evaporators share one vacuum pump?
Only if the taps and pumping speed support it. On the SHZ-D(III) the single tap pumping speed is 10 L/min, not the 60 L/min headline flow rate, and every tap in use draws on the same water ring. Size against the per-tap number.
Where to start
Start from the constraint, not the parts list. Fix your batch volume first, because that picks the flask, and the flask picks the joint: 1 L on a 24# ground joint, 3 L on a 50# flange port. Then check your material against a 1000 W bath running to 200 C with plus or minus 1 C control, and decide whether -0.095 MPa of vacuum is enough to keep it below its degradation temperature. Only then size the vacuum source, against the single tap pumping speed rather than the headline flow.
Get those four in order and assembly is trivial. Get them out of order and no amount of careful clamping will save the run. If you want the sizing worked through against your solvent and throughput rather than in the abstract, our equipment selection guide walks the same sequence, and we will confirm flask volume, condenser type, vacuum pump, cooling source, bath temperature and lift mode against your conditions before anything is quoted.