Vacuum system of freeze dryer

The freeze dryer is composed of refrigeration system, vacuum system, heating system and electrical instrument control system. The main components are drying box, condenser, refrigerating unit, vacuum pump, heating / cooling device, etc. Freeze drying, for short, is the method of freezing the water bearing substance into a solid state first, and then sublimating the moisture from the solid state to a gas state, so as to remove the moisture and preserve the substance.

Vacuum system is one of the important parts of the freeze dryer, generally including rotary vane vacuum pump or dry vacuum pump and roots vacuum pump. The function of the vacuum system is to establish a vacuum and provide the environment and conditions for the sublimation of ice. The vacuum degree of vacuum system directly affects the sublimation rate of products, and the vacuum system requires a low leakage rate. The precision of vacuum control directly affects the operation of pharmaceutical process. So, how to maintain the vacuum system of lyophilizer? Let’s have a look!

1. inspection during operation of vacuum system

Check whether the operation sound of the vacuum system is normal. If it is abnormal, check whether the three-phase power supply is balanced. Check whether the vacuum pump has abnormal vibration. Check whether the connection between the vacuum pump and the pump head is loose. If there is any, take corresponding fixing measures. For the pump with cooling water, keep enough flow and pressure difference of the cooling water. Touch one by hand during the operation The temperature of the lower pump body; for the pump with nitrogen purging, it is necessary to maintain sufficient flow and pressure of nitrogen; it is necessary to check whether the oil level is maintained at the normal level, and if it is lower than the normal level, add the specified vacuum pump oil in time; if the vacuum pump oil is emulsified, it is necessary to open the gas valve for 2 hours; if the air pump oil is discolored, it is recommended to replace the vacuum pump oil in time, clean the filter screen, and Replace the filter; observe whether the vacuum pump leaks oil, if so, shut down the pump for maintenance in time.

2. Long term shutdown inspection of vacuum system

If the pump is not used for a period of time, the power supply and cooling water supply shall be turned off; if the pump is directly turned off after the freeze-drying process, water vapor may remain in the pump body. If the pump is shut down for a long time, these liquids may corrode the mechanical structure of the pump, which may cause the pump to be unable to start again. It is recommended that the pump idle for about half an hour after commissioning.

vacuum-system-of-freeze-dryer

3. Inspection of vacuum pump head valve of vacuum system

The pump head valve is powered on at the same time when the vacuum pump is opened, and powered off when the vacuum pump stops; whether the pump head valve is powered on can be judged from the air inlet at the end of the valve. Remove the muffler, block the air inlet with your hand, if there is air to suck in, it can prove that the valve is not powered on, otherwise it is powered on; turn off the vacuum pump, cut off the power supply of the pump head valve, and judge whether the pump head valve is closed tightly through the change of the vacuum degree of the silicon pipe on the vacuum pipe.

4. Cleaning of cooling water pipe and jacket of vacuum pump in vacuum system

Connect a suitable water pipe at the water outlet and a suitable return water pipe at the water inlet; open the water inlet pipe to provide cleaning water, backwash the cooling water jacket, and flush the sediment as clean as possible; let the water flow for several minutes, then turn off the water inlet, and then disconnect the return water pipe.

5. Oil change of vacuum pump in vacuum system

Unscrew the oil drain valve, raise the oil tank of the pump body to let the old oil in the vacuum pump flow to the oil screw nut position automatically to let the oil flow out. After the old oil is drained, inject a small amount of clean vacuum pump oil (100 ~ 500ml) from the filling point of the vacuum pump, and flush the inside of the vacuum pump cavity. Then start the vacuum pump to run for about 1min, and then turn off the vacuum pump to drain the injected new oil. If the drained oil is still not dry, continue to inject new oil for flushing until it is clean. Then, tighten the oil drain valve, screw off the oil cap on the oil filling hole, add new vacuum pump oil to the vacuum pump to make the oil level reach the oil mark line, and then screw on the oil cap;

Place the container under the drain port and screw the drain port screw. Close the suction port, open the vacuum pump at the same time, open the gas ballast valve and cover the part of the exhaust port of the vacuum pump to generate a sufficient internal pressure, so that the dirty oil can be discharged quickly, and then flush the interior of the vacuum pump cavity according to the steps in step 1 above, and replace with new oil.

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