Vacuum leakage ranks among the most frequent failures of industrial freeze dryers. It will trigger side‑effects including higher power consumption, extended drying cycles and product collapse. Static pressure‑hold test is the most practical leak‑check method for pre‑shipment inspection and daily plant‑site patrol, which can evaluate overall leakage level without expensive specialized leak detectors.
Full operating procedure: after full assembly or post‑batch maintenance, tightly close chamber door. Start vacuum pumps and pull chamber down to target ultimate vacuum. After reaching set vacuum value, shut‑down all vacuum pumps and close vacuum valves to fully isolate vacuum units. Start timing and record pressure‑rise value inside chamber within fixed duration.
Acceptance criteria vary for different‑size units. General reference for food‑grade industrial freeze dryers: under room‑temperature condition, after isolating vacuum group, pressure‑rise ≤15Pa within 30 minutes means excellent performance; 15‑40Pa pressure‑rise falls within acceptable range; pressure‑rise above 40Pa indicates obvious leakage and leak‑point inspection shall be carried‑out.
Focus on frequent leak‑points: ① chamber‑door silicone sealing strip and sealing contact surface, check for debris, scratches, aging & cracks; ② gaskets of each flange joint; ③ vacuum pipe connectors; ④ sealing rings of vacuum valves; ⑤ observation window and sensor mounting ports on chamber wall.
Tips: Do not perform pressure‑hold test on hot chamber right after production run. Wait until chamber fully cools down to room temperature, because thermal expansion and contraction will distort pressure readings. Avoid test under strong wind or sharp ambient‑temperature fluctuation which interferes test results.
Pressure‑hold test can judge whether overall leakage exists, yet cannot pinpoint exact leak‑position. If pressure‑hold result fails, adopt spray‑leak‑detection to locate specific leak‑points. Re‑run pressure‑hold test after repairing to confirm qualified index. Regular pressure‑hold patrol helps discover hidden aging‑risks of sealing components in advance and prevents sudden breakdown during production.
