The following is a systematic analysis of common faults and solutions for freeze dryers,
1、 Refrigeration system malfunction
1. The compressor cannot start or stops frequently
-Possible reasons:
-Power supply phase loss or unstable voltage;
-Compressor overheating protection (condenser dust accumulation, poor heat dissipation);
-Low pressure alarm caused by refrigerant leakage;
-Compressor capacitor aging or starting relay failure.
-Solution:
-Check the three-phase balance of the power supply and stabilize it to the rated range (380V ± 5%);
-Clean the dust on the surface of the condenser to ensure the normal operation of the cooling fan;
-Leak detection (using electronic leak detector or soapy water), supplementing refrigerant (R404A/R23, etc.);
-Replace the capacitor or relay and test the insulation resistance of the compressor winding (>5M Ω).
2. Poor cooling effect (incomplete frosting on the evaporator)
-Possible reasons:
-Abnormal opening of expansion valve (ice blockage or dirty blockage);
-Insufficient refrigerant charge;
-The dry filter is clogged.
-Solution:
-Adjust the thermal expansion valve to ensure even frosting on the evaporator (preferably with condensation on the return pipe);
-Recharge the refrigerant in a quantitative manner after recycling (within ± 5% of the amount indicated on the nameplate);
-Replace the drying filter and vacuum dry the system (vacuum degree<50Pa).
2、 Vacuum system malfunction
1. The vacuum degree cannot reach the set value
-Possible reasons:
-Vacuum pump oil contamination or insufficient quantity;
-The sealing ring of the vacuum valve is aging;
-The temperature of the cold trap is too high (resulting in a decrease in ice capture capacity);
-Box leakage (deformation of door rubber strip or loosening of flange screws).
-Solution:
-Replace the vacuum pump oil (recommended to replace every 500 hours) and check the oil level window;
-Replace the fluororubber sealing ring (low temperature resistance -40 ℃~200 ℃);
-Reduce the temperature of the cold trap to below -50 ℃ (check the refrigeration system);
-Use a helium mass spectrometer leak detector to detect the box and tighten all connecting bolts.
2. Abnormal noise or smoke from the vacuum pump
-Possible reasons:
-Improper treatment of inlet water in the pump chamber (water vapor reflux);
-Rotor wear or blade fracture;
-Motor overload (unstable voltage or stuck bearings).
-Solution:
-After shutting down, drain the water from the pump and replace the lubricating oil;
-Disassemble the pump body and check the rotor clearance (0.1~0.2mm), replace damaged parts;
-Check the motor current, repair the bearings or replace the pump head.
3、 Heating system malfunction
1. The temperature of the partition is uneven or not heating up
-Possible reasons:
-Heating tube open circuit or poor contact;
-Temperature sensor (PT100) offset;
-The solid-state relay (SSR) is damaged.
-Solution:
-Use a multimeter to measure the resistance of the heating tube (usually tens to hundreds of ohms);
-Calibrate the temperature sensor (if the error is greater than ± 1 ℃, it needs to be replaced);
-Replace the SSR module and check the output signal of the control board.
2. Slow heating rate
-Possible reasons:
-The insulation layer is damaged (polyurethane foam inside the box falls off);
-Heating power attenuation (aging of nickel chromium alloy after long-term use).
-Solution:
-Repair the insulation layer or install insulation cotton;
-Increase the heating voltage (not exceeding 10% of the rated value) and replace the heating plate if necessary.
4、 Control system malfunction
1. Program running exception (such as stage jump failure)
-Possible reasons:
-PLC program logic error or low battery level;
-Touch screen communication interruption;
-Sensor signal interference (strong electric field environment).
-Solution:
-Reset the PLC program after backup and replace the battery (CR2032);
-Check if the RS485 communication line is virtual;
-Shield the signal lines of the control cabinet and keep them away from interference sources such as frequency converters.
2. Abnormal parameter display (such as large fluctuations in vacuum degree)
-Possible reasons:
-The vacuum gauge is damp or the probe is contaminated;
-Loose wiring leads to signal drift.
-Solution:
-Disassemble the vacuum gauge and dry it in a 60 ℃ oven for 2 hours, then calibrate the zero point;
-Tighten the aviation plug and check if the shielding layer is grounded.
5、 Operational faults
1. Poor freeze-drying effect of samples
-Possible reasons:
-Insufficient pre freezing (high liquid content in the sample);
-The sublimation rate is too fast (the temperature of the partition is too high);
-The material is too thick (>15mm).
-Solution:
-Extend the pre freezing time (maintain below -40 ℃ for 4 hours);
-Gradual heating (primary stage ≤ -20 ℃);
-Control the thickness of the material (recommended<10mm) and increase stirring.
2. Severe frost return after shutdown
-Possible reasons:
-Not executing the 'defrosting program' before shutting down;
-The pneumatic valve is not tightly closed.
-Solution:
-Start up and execute high-temperature defrosting (raise the partition temperature to 25 ℃);
-Check the sealing of the solenoid valve and clean the ice residue at the valve port.
6、 Preventive maintenance recommendations
1. Daily inspection: Record the oil level of the vacuum pump, the amount of ice in the cold trap, and the voltage and current;
2. Monthly maintenance: clean the condenser fins and check the water pipe joints;
3. Annual maintenance: replace refrigerant, test motor insulation resistance, and verify sensors;
4. Long term disuse: Cover with dust-proof cloth, close the water vapor valve, and cut off the power supply.