The core principles of vacuum drying oven operation are: slow pressure release, strict prohibition of explosive materials, prevention of back-siphonage, and adherence to temperature limits. Operators must strictly follow the prescribed power-on/power-off sequence and perform routine daily maintenance.
I. Pre-Operation Preparations
Environment and Grounding: Place the unit on a level countertop in a well-ventilated, dry area free from corrosive gases and strong vibrations. Leave a clearance of 30–50 cm on all sides to allow for heat dissipation. The unit's outer casing must be reliably grounded.
Equipment Inspection:
Ensure the door seal gasket is intact and free of cracks; apply a small amount of vacuum grease if necessary. The door latches should be tightened to an appropriate tension.
Verify that the vacuum pump oil level is between the 1/2 and 2/3 marks on the sight glass, and that the oil is clear and shows no signs of emulsification.
Ensure all pipeline connections are tight, undamaged, and free of leaks.
Sample Requirements:
Strictly prohibit the placement of flammable, explosive, highly corrosive, or highly volatile organic solvent-containing samples (e.g., ethanol, acetone, strong oxidizers) inside the oven.
Samples containing large amounts of moisture or solvents should undergo preliminary drying at atmospheric pressure first. For powdered or fine-granular samples, install a barrier screen at the vacuum port to prevent particles from being drawn into the pump.
Samples should be laid out flat rather than stacked, and their total volume must not exceed half of the oven's internal capacity. Maintain a clearance of at least 5 cm between the samples and the oven walls/door, and a clearance of at least 2 cm between shelves.
II. Power-On and Operation Procedures
Door Sealing: Close the oven door and tighten the door latches evenly to ensure a tight seal with no air leaks.
Vacuum Pumping (Vacuum First, Then Heating):
Open the vacuum valve → Start the vacuum pump → Monitor the vacuum gauge until the target vacuum level is reached (typically -0.08 to -0.095 MPa). Once the target is reached, close the vacuum valve *first*, and then turn off the vacuum pump. If the vacuum level drops below the target, repeat this step.
Do not allow the vacuum pump to run continuously for extended periods; operate it intermittently (start/stop cycles) to prolong its service life. Heating and Temperature Control:
Once the vacuum stabilizes, activate the heating system and set the target temperature (typically 40–80°C; maximum ≤200°C, depending on the specific model).
For heat-sensitive samples, keep the temperature ≤40°C. For solvent-containing samples, first apply a vacuum at room temperature to remove the solvent, then gradually increase the temperature to prevent bumping (sudden, violent boiling).
Operation Monitoring:
During the first 30 minutes, record the temperature and vacuum level every 15 minutes; once stable, record them every hour. Ensure temperature fluctuations remain within ±2°C and that the vacuum level remains stable without any continuous decline.
In the event of any abnormality (e.g., overheating, air leaks, unusual noises, or strange odors), immediately turn off the heating system → close the vacuum valve → stop the pump → cut off the power supply, and troubleshoot the issue.
Opening the chamber door while drying is strictly prohibited (the negative pressure can easily cause the glass door to shatter or cause samples to be ejected).
III. Completion and Shutdown (Critical: Preventing Backflow)
Turn off Heating: First, deactivate the heating system and allow the chamber to cool naturally until the temperature drops below 60°C.
Slow Venting (Most Critical Step):
Slowly turn the air release valve to allow air to enter gradually. Wait until the vacuum gauge returns to zero (approximately 3–5 minutes). Rapid venting is strictly prohibited, as it can scatter the samples and damage the chamber structure.
Sample Retrieval: Once you have confirmed that the internal and external pressures are balanced, open the chamber door. Wear heat-resistant gloves when retrieving samples to prevent burns.
Shutdown Sequence: Turn off heating → Close vacuum valve → Stop vacuum pump → Cut off main power supply → Clean the chamber.
IV. Safety Prohibitions
❌ Opening the chamber door while under vacuum; or opening the door immediately after venting while the temperature is still >80°C.
❌ Drying flammable, explosive, highly corrosive, or highly volatile samples.
❌ Stopping the vacuum pump without first closing the vacuum valve (this causes pump oil backflow, contaminating the interior of the chamber).
❌ Operating the power switches with wet hands; or operating the equipment without proper grounding.
V. Routine Maintenance
After Each Use: Allow the chamber to cool below 40°C. Use a soft cloth dampened with a neutral detergent to clean the interior chamber, then wipe it dry. Lightly coat the door seal with silicone oil or petroleum jelly for maintenance.
Vacuum Pump: Change the pump oil every 500 hours or every 3 months. Clean the air intake filter to prevent clogging by dust or particles.
For Long-Term Storage: Leave the chamber door slightly ajar to allow for ventilation. Cut off the power supply. Drain the water tank (if applicable). Cover the unit to protect it from dust.