What to Do If Rotary Evaporator Cannot Draw Vacuum？

The vacuum rotary evaporator is an essential laboratory instrument, widely used for evaporation, purification, and concentration of samples. It typically consists of a distillation flask, rotary motor, condenser, heating bath, constant temperature tank, vacuum pump, vacuum buffer bottle, and sealing ring.

However, during operation, users may encounter situations where the rotary evaporator cannot draw vacuum, which directly affects efficiency and experimental results. Below are the main causes and practical solutions.

I. Possible Causes

1. Residual Solvent
   Excess solvent in the container may limit the saturated ejector pressure, preventing the system from reaching proper vacuum levels.

2. Vacuum Pump Performance
   The vacuum pump may have reduced capacity due to long-term use, oil contamination, or mechanical wear.

3. Pipeline and Connection Leaks
   Loose vacuum hoses, worn joints, or a leaking vacuum gauge may reduce airtightness.

4. System Airtightness Issues
   Perform a pressure test: with no solvent present, close all butterfly valves and pipelines, then maintain pressure for one minute. If the vacuum gauge needle remains stable, the airtightness is intact.

5. Valve Blockage
   Debris in the discharge valve or pressure control valve may hinder proper airflow.

6. Damaged Components
   Issues with the glass wool sandwich panel or sealing rings can lead to leaks and poor vacuum performance.

II. Solutions

1. Drain Solvent
   Empty reagent bottles and remove residual solvent to avoid pressure interference.

2. Maintain the Vacuum Pump
   Clean and repair the pump by changing pump oil or water, depending on the pump type.
   For stable performance, using a diaphragm vacuum pump with a rotary evaporator is often recommended.

3. Check Vacuum Pipelines
   Inspect hoses, connections, and vacuum gauges for leaks. Replace damaged parts if necessary.

4. Reassemble and Seal
   Clean the ground edges of the sandwich panel, apply vacuum silicone grease, align and tighten the flanges, and replace faulty seals.

5. Clean Valves
   Remove any debris in the discharge valve and pressure control valve to restore normal operation.

6. Repair or Replace Panels
   If the glass wool sandwich panel is damaged, repair or replace it to ensure airtightness.

Advantages of Rotary Evaporator

The laboratory rotary evaporator offers multiple advantages:

• Compact structure and efficient design

• Intuitive operation

• High evaporation efficiency

• No metal ion contamination

• Suitable for laboratories, pilot production, and extraction of precious materials

For large-scale applications, the 50L rotary evaporator provides higher throughput with reliable vacuum performance.

Conclusion

When a rotary evaporator cannot draw vacuum, troubleshooting should focus on solvents, vacuum pump condition, pipeline airtightness, and valve cleanliness. Proper maintenance and timely replacement of worn components can restore efficiency and ensure long-term reliable operation.

For more details, explore our full range of Nanbei Instruments Rotary Evaporators.