How to Size a Chiller and Vacuum Pump for a Rotary Evaporator

How to Size a Chiller and Vacuum Pump for a Rotary Evaporator

A rotary evaporator is only as good as the vacuum pump and the cooling behind it. Too weak a pump and the solvent will not boil at a safe bath temperature. Too warm a condenser and solvent vapour escapes into the pump and the room instead of collecting in the receiving flask. This guide shows how to choose both for your work.

Step 1: Know the vacuum each solvent needs

The table shows roughly how far the pressure must drop for common solvents to boil at about 40°C. That vapour temperature works well with a 60°C bath and a condenser at 20°C or colder.

Solvent Approx. pressure for boiling at 40°C Pump that is enough
Acetone about 556 mbar Any PT-89 diaphragm model
Hexane about 335 mbar Any PT-89 diaphragm model
Methanol about 337 mbar Any PT-89 diaphragm model
Ethyl acetate about 240 mbar PT-89 27″ Hg model
Ethanol about 175 mbar PT-89 27″ Hg model
Water about 72 mbar PT-89/35 piston type (29.5″ Hg)

To compare with pump specifications: a gauge reading of 22″ Hg is roughly 270 mbar absolute, 27″ Hg roughly 100 mbar, and 29.5″ Hg roughly 17 mbar. Choose a pump that goes comfortably below what your solvent needs, because hoses, joints and glassware always leak a little.

Step 2: Choose the vacuum pump

  • Go oil-free. Solvent vapour dissolves in pump oil, so an oil-sealed pump needs frequent oil changes and puts oil mist into the lab. An oil-free diaphragm pump such as the PT-89 avoids both.
  • 27″ Hg for most work. PT-89/10 (15 L/min) or PT-89/20 (60 L/min) handle ethanol, ethyl acetate and other common solvents. The higher flow of the PT-89/20 pulls down faster on larger glassware.
  • Corrosive vapours: choose the PTFE-coated PT-89/30 (28 L/min, 27″ Hg).
  • Water and high-boiling solvents: choose the piston-type PT-89/35 (60 L/min, 29.5″ Hg).
  • Control the vacuum. A vacuum gauge with regulator (PT-89/25) lets you reduce the vacuum gently, so the sample does not bump or foam.

Step 3: Set the cooling with the 20/20/20 rule

Keep about 20°C between each stage:

  • Bath: about 20°C above the vapour temperature, for example 60°C.
  • Vapour: the solvent boiling at your working vacuum, for example 40°C.
  • Condenser coolant: about 20°C below the vapour, for example 20°C or colder.

Coolant colder than this recovers even more solvent and lets you work at a lower bath temperature for heat-sensitive samples. In much of India, tap water is 25–35°C for much of the year, which is too warm for reliable recovery of low-boiling solvents. That is the main reason labs add a chiller.

Step 4: Size the chiller

The PT-80 recirculating chiller cools from ambient down to −10°C with ±1°C PID control and a built-in circulation pump. Choose the size by what it cools:

Set-up Suggested PT-80 model
One bench rotary evaporator 6.5 L, 30 LPM (PT-80/05 or SS PT-80A/05)
Larger condenser, or two instruments 12 L, 30 LPM (PT-80/10 or PT-80A/10)
Jacketed reactor, or several instruments 22 L, 40 LPM (PT-80/15 or PT-80A/15)

For a GMP area, choose the SS 304 body (PT-80A models). The optional 2000 W heater lets the same unit heat coolant up to 70°C for jacketed-reactor work.

A complete rotary evaporator system

A typical set-up for a pharma or research lab:

All three are made by Popular Traders in Ambala. They carry a 1-year warranty and are mostly ready stock, dispatched in about 2–3 days, with installation and training at your lab anywhere in India. Not sure what you need? Read how to choose a rotary evaporator, or tell us your solvents and we will size the system for you.

Frequently asked questions

What vacuum level does a rotary evaporator need?

It depends on the solvent. Most organic solvents evaporate well at 100–350 mbar, which a 27″ Hg diaphragm pump reaches. Water needs about 70 mbar or lower, so use a deeper-vacuum pump.

Can I use tap water instead of a chiller?

You can, but in Indian conditions tap water is often too warm to condense low-boiling solvents fully. A chiller recovers more solvent, saves water and gives consistent results all year.

What temperature should the chiller be set to?

About 20°C below the solvent’s vapour temperature. For most work, 0–10°C is ideal, and the PT-80 can go down to −10°C.

Why use an oil-free vacuum pump with a rotavap?

Solvent vapour contaminates pump oil. An oil-free diaphragm pump needs no oil changes and does not release oil mist into the lab.

How do I get a recommendation for my lab?

WhatsApp 8199900060 or email popular1942@gmail.com with your solvents and batch size, or use “Make an enquiry” on any product page.