Article**labconco official website:
Vacuum system is one of the important parts of the freeze dryer, in the freeze drying process, the moisture in the product can only be sublimated in a certain vacuum state to achieve the purpose of drying. The operation effect of the vacuum system will directly affect the quality and production cycle of lyophilized products. In view of this, the causes and solutions of common faults in the vacuum system of the lyophilizer were analyzed.
The lyophilizer is the key equipment for the production of lyophilized preparation products, and the vacuum system is an important part of the lyophilizer, which is mainly composed of drying oven, condenser, vacuum pump, roots pump, small butterfly valve, box trap isolation valve (large butterfly valve, mushroom valve), vacuum testing device [vacuum instrument, vacuum gauge (pressure sensor)], gas release device, auxiliary device, vacuum pipeline, etc.
The schematic diagram of the vacuum system is shown in Figure 1, the system adopts a vacuum pump group, forms a strong suction capacity, forms a vacuum in the drying chamber and the condenser, on the one hand, promotes the water in the drying chamber to evaporate (sublimation) in the vacuum state, on the other hand, this vacuum system forms a vacuum gradient (pressure difference) between the condenser and the drying chamber, so that the moisture in the front box is captured by the condenser after sublimation.
The operation effect of the freeze dryer vacuum system will directly affect the quality and production cycle of the freeze-dried preparation products, therefore, do a good job in the maintenance of the freeze dryer vacuum system, and solve the current faults in the operation process in a timely manner to ensure production.
Smooth progress and product quality are of great importance.
1 Vacuum leakage analysis and treatment due to valve diaphragm damage.
Fault phenomenon: When the freeze dryer runs the UT program leakage rate test, it is found that the vacuum value gradually rises, and the vacuum value rises by 1 Pa (10 bar) in 10 min, which exceeds the allowable value [10 min rise is less than or equal to 0.].8 PA (8 bar)], a vacuum alarm appears on the interface.
The failure analysis method is shown in Figure 2.
Solution: 1) Check the surface of the vacuum probe and the communication is not abnormal, replace the new vacuum metering probe and test, the same situation occurs, so the cause of the vacuum probe is ruled out.
2) Sterilization and drying, followed by UT test, the same situation occurs, so the cause of water vapor is ruled out.
3) Manually open the UT test, when the vacuum value is pumped to a certain value, manually close the mushroom valve to detect the leakage position. After closing the mushroom valve, it is found that the front box has the advantages of longer life, which is more conducive to the long-term efficient and stable operation of the cathode line of the electrostatic precipitator, which can ensure the normal electric field of the electrostatic precipitator and improve the dust removal efficiency of the electrostatic precipitator.
If the null value rises gradually, and the vacuum value of the cold trap remains unchanged, it is judged that the front box is leaking;Then close the front box inlet valve 6v1, find that the front box vacuum value is still gradually rising, then judge that the front box leakage, not the air inlet section leakage is caused by the influence;Then check the door sealing ring of the front box, the feeding door sealing ring, the discharging small door sealing ring, and no abnormality was found;Then the valve gasket connected to the cavity of the front box was disassembled and inspected, and finally it was found that the vacuum leakage was caused by the damage of a valve diaphragm in the front box. Immediately after that, the valve diaphragm was replaced, and the vacuum test was carried out after the replacement, and no abnormality occurredThen it was cleaned and sterilized, and then the vacuum test was carried out, and there was no abnormality, and the final vacuum leakage rate was qualified.
2. Analysis and treatment of overload protection of water ring vacuum pump.
Fault phenomenon: The water ring vacuum pump suddenly stops running during the SIP process of the freeze dryer, the circuit breaker is automatically disconnected, and the operating computer appears to give an alarm of "water ring vacuum pump failure".
The failure analysis method is shown in Figure 3.
2.1 Power supply check.
Operation method: Use a metered multimeter, adjust to 1 000 V AC file, and detect the power supply of the upper and lower pile heads of any two groups of line circuit breakers.
380～ 420 v。
Result analysis: The voltage of the upper and lower pile heads of any two groups of power lines is about 398 V, indicating that there is no problem with the power supply ** and the circuit breaker.
2.2 Motor coil inspection.
Operation method: Use a qualified multimeter, adjust to 200 resistance gear, and detect the resistance value of the three sets of coils of the motor.
Result analysis: detect the resistance value of three groups of coils of the motor, and the resistance value of the three groups is the same, indicating that there is no problem with the motor coil.
2.3 Water source** inspection.
Operation method: Manually open the drinking water line valve, and the water source pressure is at 019 MPa, the pressure is as required, and the water ring pump drain is slowly opened.
Result analysis: The inspection found that the water outlet pressure of the drainage outlet was large, indicating that the pipeline was smooth and the water supply was normal.
2.4. Impeller operation inspection.
Operation method: Remove the rear end cover of the motor, manually dial the rotor, and it cannot be rotated.
Result analysis: It can be basically judged that the fault is the circuit overload protection caused by the mechanical fault of the motor.
Solution: Disassemble the water ring vacuum pump as a whole, transfer it to the maintenance room, find that the impeller is missing a piece after removing the pump head, check the inside of the pump head, find that the missing blades have stuck the impeller, use professional tools to remove the impeller on the special machine, and replace the impeller with a new one.
The results were confirmed: the water ring vacuum pump was reinstalled, the program was run, the equipment was working properly, and the problem was solved.
3. Vacuum system leakage analysis and treatment.
Fault phenomenon: the vacuum of the freeze dryer is abnormal, the pressure rise test is unqualified, and the fault is manifested as the freeze dryer pumping limit vacuum is 65 PA (65 bar), 1 PA (10 bar) set by the device cannot be reached.
The failure analysis method is shown in Figure 4. 
Fig.4. Vacuum pumping limit analysis.
3.1. Check the vacuum pumping performance of the vacuum pump.
Operation method: In the freeze dryer shutdown state (all valves connected to the freeze dryer are closed in the shutdown state), manually open a rotary vane vacuum pump, observe whether the ultimate vacuum can be reached, close the vacuum pump, and then observe the vacuum change of the pump head.
Result analysis: During the manual pressure rise test, the number of vacuum probes in the front box rebounded, and rose by 3 per minute2 pa (32 bar) with an infinite upward trend.
Solution: Disassemble all the quick card connections connected to the vacuum pump, replace them with new sealing rings, and apply vacuum grease to the connections at the same time (some quick cards are found to be loose during disassembly, and some sealing rings are seriously aged), and re-vacuum test after replacement.
The results were confirmed: the vacuum pump was pumped to 0 in the ultimate vacuum7 Pa (7 bar), the pump head does not pick up after the vacuum pump is closed, and the cause of vacuum pump and pipeline leakage can be ruled out.
3.2. Leak detection of the rear box and all pipes, valves, and quick card connected to the rear box.
Operation method: First, install a digital vacuum probe in the back box, and the freeze dryer runs a no-load program to pump the box to the ultimate vacuum [set to 1 pa.]
Resulting in circuit overload protection.
Solution: Disassemble the water ring vacuum pump as a whole, transfer it to the maintenance room, find that the impeller is missing a piece after removing the pump head, check the inside of the pump head, find that the missing blades have stuck the impeller, use professional tools to remove the impeller on the special machine, and replace the impeller with a new one.
The results were confirmed: the water ring vacuum pump was reinstalled, the program was run, the equipment was working properly, and the problem was solved.
3. Vacuum system leakage analysis and treatment.
Fault phenomenon: the vacuum of the freeze dryer is abnormal, the pressure rise test is unqualified, and the fault is manifested as the freeze dryer pumping limit vacuum is 65 PA (65 bar), 1 PA (10 bar) set by the device cannot be reached.
The failure analysis method is shown in Figure 4.
Vacuum pumping is not limited to analysis.
3.1. Check the vacuum pumping performance of the vacuum pump.
Operation method: In the freeze dryer shutdown state (all valves connected to the freeze dryer are closed in the shutdown state), manually open a rotary vane vacuum pump, observe whether the ultimate vacuum can be reached, close the vacuum pump, and then observe the vacuum change of the pump head.
Result analysis: During the manual pressure rise test, the number of vacuum probes in the front box rebounded, and rose by 3 per minute2 pa (32 bar) with an infinite upward trend.
Solution: Disassemble all the quick card connections connected to the vacuum pump, replace them with new sealing rings, and apply vacuum grease to the connections at the same time (some quick cards are found to be loose during disassembly, and some sealing rings are seriously aged), and re-vacuum test after replacement.
The results were confirmed: the vacuum pump was pumped to 0 in the ultimate vacuum7 Pa (7 bar), the pump head does not pick up after the vacuum pump is closed, and the cause of vacuum pump and pipeline leakage can be ruled out.
3.2. Leak detection of the rear box and all pipes, valves, and quick card connected to the rear box.
Operation method: First, install a digital vacuum probe in the back box, and the freeze dryer runs a no-load program to pump the box to the ultimate vacuum [set to 1 pa.]
10 bar), but only 65 pA (65 bar)], turn off the no-load program, and observe the value of the digital vacuum probe to pick up.
Result analysis: There is a certain change in the value of the digital display probe, and the back box belongs to the micro leakage.
Solution: Disassemble all the quick card connections directly connected to the back box, replace the new sealing rings, and apply vacuum grease to the connections at the same time (some of the sealing rings are found to be seriously aged during disassembly), and re-vacuum test after replacement.
The results confirmed: there was no change in the value of the digital display probe, and the cause of the leakage of the back box could be ruled out.
3.3. The front box and all pipes, valves, and quick cards connected to the front box are sealed and leaked.
1) After the lyophilizer program is turned offAfter the front box is pumped out of the ultimate vacuum, the machine is stopped to observe the vacuum recovery of the front box.
Operation method: The freeze dryer runs the no-load program to pump the limit of the box to the true empty [set to 1 pa (10 bar), but the actual pumping is only 6.].5 pA (65 bar)], close the no-load program, and observe the value of the vacuum probe in the front box to recover.
Result analysis: After the closing procedure, the value of the probe of the front box has rebounded, that is, the pipe seal and valve directly connected to the front box have leakage.
Solution: Disassemble all the pipe seals and valve connections directly connected to the front box, replace the new sealing rings, and apply empty grease at the connections at the same time (some of the sealing rings are found to be seriously aged during disassembly), and re-vacuum test after replacement.
The results were confirmed: the freeze dryer ran a no-load program to pump the chamber to the limit of vacuum [set to 1 pa (10 bar), but it was still only pumped to 6.].5 pa (65 bar)], turn off the no-load program, observe that the value of the vacuum probe in the front box does not rise, and the cause of the leakage in the front box is eliminated.
2) The freeze dryer program is runningAfter the ultimate vacuum is pumped in the front box, the pressure rise is observed by closing the mushroom valve (pressure rise test).
Operation method: The freeze dryer runs the no-load program to pump the box to the limit [set to 1 pa (10 bar), but the actual pumping is only 6.].5 pA (65 bar)], close the no-load program, and observe the value of the vacuum probe in the front box to recover.
Result analysis: After the closing procedure, the value of the probe of the front box has rebounded, that is, the pipe seal and valve directly connected to the front box have leakage.
Solution: After the investigation and leak detection of the previous step, the freeze dryer does not have a vacuum rise phenomenon in the front box after the shutdown, but the vacuum probe value rises infinitely when the manual pressure rise test is carried out in the program operation, and only the valve after 6v1 is open in the program operation, so it can be judged that the leakage point should be on the pipeline after 6v1. The 6v1 rear end pipe is a nitrogen inlet pipe, and the pipeline is connected in three sections with 5 seals.
rings, 8 pneumatic valves and 1 nitrogen filter. Among them, 4 valves are closed, respectively, 6VVVv31, and 6VV4, 5V40A, 5V40B are nitrogen inlet valves and regulating valves, all sealing rings on this pipeline are replaced, and 4 pneumatic valve diaphragms are deformed and all replaced. The housing of the nitrogen filter element is disassembled, the O-ring is re-applied with vacuum grease, and the no-load program is re-run for manual pressure rise test after replacement.
The results were confirmed: the freeze dryer ran the no-load program to pump the chamber to the limit of vacuum [set to 1 pa (10 bar), the actual can reach 0.].8 pA (8 bar)], the pressure rise test was performed manually, and the result was 01 pa min (1 bar min), qualified.
The results of the ultimate vacuum test of the lyophilizer are: start vacuuming, from positive pressure 1009 108 MPa (1 009 mbar) pumped to 0 in 15 min, from 0 to 08 pA (8 bar) took 22 minutes, and the pressure rise test result was 01 pa/min（1 μbar/min）。
4. Analysis and treatment of abnormal air intake branch of vacuum system.
Fault phenomenon: the vacuum system of the freeze dryer was pumped to the set value of 1 pa (10 bar) within 35 min to meet the requirements during the no-load test, and it took 50 min to pump to 100 pa (1 mbar) on the same day, and the system did not meet the process production requirements and needed to be overhauled.
The failure analysis method is shown in Figure 5.
Analysis of intake branch anomalies.
4.1 Solution.
4.1.1. Leakage investigation of lyophilization box.
The pipeline seals, valves, blind plates, safety valves, product probe connections, sight glasses, door seals and bellows seals of the freeze-drying box directly connected to the freeze-drying box are all disassembled, the sealing ring made of polyethylene material is replaced, and the high-vacuum silicone grease is applied to the connection at the same time, and the vacuum test is carried out again after the replacement.
In the case that the leakage is difficult to find, a single component or branch can be disassembled, and the blind plate is used to block, first to ensure that the whole does not leak, and then one by one to install the test, which part is abnormal after the installation test, and the position is locked for investigation. This method is time-consuming, the effect is obvious, and it is necessary to have a variety of specifications of blind plates.
After excluding the non-leakage of the box, check the rise of the vacuum value after manually disconnecting the intake branch, and if the value does not change, the downstream will not leak;If counted.
If the value rises, there is a leak and needs to be checked one by one.
4.1.2. Leakage investigation of air intake branch.
When the manual pressure rise test is carried out in the program operation, the vacuum probe value rises indefinitely, and only the valve of 6v1 backwards is open in the program operation, so it can be judged that the leakage point should be on the pipeline behind 6v1 (6v1 is the air inlet valve of the freeze-drying box, and this pipeline plays the role of supplementing nitrogen in the box to keep the vacuum degree at the set value when vacuuming).
As shown in Figure 6, the pipeline is connected in three sections, with 5 sealing rings, 8 pneumatic valves, and 1 nitrogen filter. Replace the pipe seals and valve gaskets and filter housing seals in sections, and re-run the program for testing after the replacement is completed.
Intake lines. 4.2 Summary.
The inspection of the vacuum system is the third stepThe freeze-drying box, the condensing chamber, and the air intake branch are precisely the air intake branches that are easy to ignore. The intake branch is often thought to be just a few valves and filters, which are not expanded by steam, and the gasket does not age significantly, and the possibility of leakage is not large. However, the neglected areas are often the most prone to abnormalities, and it is necessary to pay attention to all aspects of maintenance in ordinary maintenance.
5 Conclusion. The lyophilizer vacuum system plays a decisive role in the freeze-drying process and product quality, and this paper analyzes the common faults of the lyophilizer vacuum system and proposes solutions, hoping to play a certain role in helping the freeze-dryer equipment managers.