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Your location: Home > Related Articles > Repair and maintenance of food low temperature freeze dryer

Repair and maintenance of food low temperature freeze dryer

Author:QINSUN Released in:2023-04 Click:130

1. Routine cooling system maintenance

(1) Routine inspection before every boot:

1) All valves (compressor suction and discharge valves, liquid supply valves, hand valves, etc.) is open;

2) Whether the pressure gauge readings are normal (0.6~0.7 MPa );

3) Whether the compressor oil level is normal (1/4~3/4); 4) Whether the cooling water pressure (above 0.1MPa) and the temperature normal.

(2) Note after power transfer:

1) Whether the compressor automatically liquid opvangt;

2) Whether the oil pressure differential is reset, etc.;

3) Check the crankcase heater, the temperature of the crankcase should be 20℃ higher than ambient temperature.

(3) Note after startup:

1) Is the sound of the compressor normal;

2) Whether there is abnormal vibration in the refrigerant pipe;

3) Whether the vibration of the compressor itself is minimal ;

4) Whether the sight glass flow is normal;

5) expansion valve junction frost condition;

6) Compressor frost return.

(4) Compressor refrigeration oil should be changed every six months or every year, depending on the situation.

(5) The water condenser should be cleaned regularly, usually 1 It can be disassembled and washed , and can also be cleaned with a water treatment detergent. For air-cooled units, clean the outside surface of the condenser in time.

(6) Note that the compressor cannot be started often and the time between starts Must be greater than 3 min.

2. Common problems and solutions

2.1 High pressure too high , high pressure alarm

(1) There is too much refrigerant and the outlet pressure is high, so some of the refrigerant must be released.

(2) The cooling water temperature is high, the flow rate is insufficiente whether the water condenser is calcified.

(3) There is a leak in the low pressure part of the refrigerant pipe, breathing air.

(4) The high pressure exhaust valve is not fully opened or damaged, resulting in poor exhaust.

It can be reset via the fire alarm reset button and the button switch is on the high voltage pressure relay.

2.2 Differential oil pressure alarm

(1) The oil return is not smooth, resulting in an insufficient oil level in the compressor crankcase, and the oil pump cannot absorb oil. Generally, the oil separator should be be replaced with a new one.

(2) The oil is dirty and the oil pump filter is clogged. Need to change the oil and clean the oil filter.

(3) The oil pressure differential relay is not working. Replace it with a new oil pressure differential relay.< /p

(4) The oil pump is defective. Replace with a new oil pump.

(5) The evaporation of the cooling system is not good and the coolant enters the crankcase. The cooled oil is introduced into the system, causing the oil pressure to become too low. Turn off the fluid supply. valve at the condenser outlet or adjust the thermal expansion valve (increase system superheat).

The oil pressure differential relay operates 90 seconds after the compressor starts, if there is no oil pressure differential, the alarm will sound. After the alarm, the reset button can be used on the oil pressure differentialais must be reset to eliminate the alarm.

2.3 Compressor thermal protection ( motor temperature over 85 ℃)

The return air volume of the system is insufficient and the motor is not cooled sufficiently.


(1) Adjust the intercooler expansion valve to increase the circulation of the system to fully cool the engine.

(2) Check whether the liquid supply line is blocked (liquid supply valve, drying filter, solenoid valve, filter screen for the expansion valve, etc.), such as blockage to be solved.

(3)Check the return air line and the compressor Check if the suction filter is clogged and repair if clogged.

(4) Check whether there is a shortage of refrigerant, if it is missing, it must be replenished. After the alarm of the electronic thermal protector, switch off the 220 V control power supply of the thermal protection off and restart to clear the alarm.

2.4 Water pressure alarm

(1) The cooling water pressure is lower than the druk set by the water pressure relay. It is necessary to ensure that the cooling water pressure is higher than the pressure set by the water pressure relay. pressure relay; If there is no alarm, the pressure set by the water pressure relay can be properly reduced.

(2) The water pressure relay is invalid. The water pressure relay needs to be replaced.

As long as the water pressure is higher than the pressure set by the water pressure relay, the alarm will be eliminated.

2.5 compressor cannot start

(1) One of the alarms of high pressure alarm, oil pressure differencealarm, electronic thermal protection and water pressure alarm. It is necessary to find the cause of the alarm and rectify the alarm.

(2) The instantaneous start-up current is too large, resulting in thermal overload protection or air switch protection. It is necessary to find out the cause of the large current and then start after resetting the thermal overload.

(3) The compressor crankshaft is jammed and the piston cylinder is jammed. The compressor needs to be repaired.

(4) Check system error, there is no output control for the compressor. This needs to be resolved by our software personnel.

(5) Electrical system failures such as PLC failures, AC switch failures, etc. have attached electrical components, replace them

2.6 The compressor automatically stops while running

(1) High pressure alarm, oil pressure differential alarm, electronic thermal protection, water pressure alarms have at least one of them.

(2) AC breaker faulty, overload protection, compressor motor suddenly burned out during operation.

(3) Fluid shock or oil shock occurs during operation and piston or crankshaft seizes.

(4) When the driver is running, the driver is temporarily unstable, suddenly no output.

2.7 The cooling effect of the cooling system is not good

(1) The opening of the expansion valve is too large or too small. The expansion valve is open too far. The machine reaches the best working condition.

(2) The cooling system is blocked, for example, the filter is blocked, the expansion valve is blocked, and the relevant valves arenot opened or completely closed Open, solenoid valve malfunction, etc. It is necessary to find the location and cause of the blockage and clean it in time.

(3) Insufficient refrigerant. the correct amount of refrigerant must be added.

(4) The paper packageg on the upper part of the compressor valve plate or the lower part of the cylinder is defective or broken or the compressor is sucked out and exhausted. The valve piece is broken. It should be replaced with a new paper block or exhaust valve piece.

3 general maintenance measures

3.1 Tracking leaks

(1) Pressurize the system, fill it with nitrogen to 1.4 MPa and record the readings of each gauge after the four pressure gauges of high, medium, low and oil in equilibrium, after holding pressure for several hours (usually more than 24 hours), check that the readings of the pressure gauges drop. If they drop, it indicates a leak in the system. Use soapy water to remove suspected leak detection points.

(2) The basic premise of checking any suspicious point with a halogen lamp is that the system has refrigerant and the readings of the four meters are balanced (above 0.5 MPa) .

(3) Use an advanced leak detector, such as a helium mass spectrometer, to evacuate the pipeline first, then pump it to the limit Turn off the vacuum pump, switch to a helium mass spectrometer to evacuate and spray helium gas to the suspected leak point Via the instrumentdisplay on the helium mass spectrometer you can see the specific location of the leak point with very high accuracy.

3.2 Charge refrigerant

(1)Be sure to confirm the quality of the refrigerant before charging, Charge after confirming that there is no quality problem.Inferior quality refrigerants are extremely destructive to the compressor and refrigeration system, affecting the operation of the refrigeration system in the slightest and damaging the compressor in severe cases.

 (2) It can be filled through the lagepressure suction port of the compressor. enter the cooling system.

(3) Before charging refrigerant, determine whether the system will be fully or additionally charged, if it is the former (special< /p>

(not for those who have just done pressure maintenance and leak detection), theit is recommended to vacuum the system first; for the latter, vent the air into the system for cleaning. Refrigerant must be replenished appropriately.

(4) If the refrigerant is azeotropic, it is not necessary to turn the cylinder upside down and lay it flat and fill it directly into the system; if it is a non-azeotropic refrigerant, you can consider turning the cylinder upside down and laying it flat (that is, the exhaust is in a liquid state), but the valve at the opening of the refrigerant tank should be closed as small as possible to prevent liquid shocks in the compressor.

(5) Before charging, make sure the connected pipe is not leaking, connect it to the outlet of the refrigerant tank, and then open the valve to let the refrigerant into the connected pipe to drain. Then connect the other end of the connecting pipe to the angle valve on the gas-liquid separator; note the pressure readings of each pressure gauge, the number of bubbles on the sight glass and the amount of defrosting of the compressor to determine the amount of refrigerant.

3.3 Adjusting the expansion valve

(1) Rotate clockwise to adjust The flow rate of the expansion valve is small, and the flow rate of the expansion valve can be increased counterclockwise.

(2) Compressor suction The amount of ice on the mouth and the number of bubbles in the sight glass can indirectly reflect the opening degree of the expansion valve. When adjusting the expansion valve, the adjustment amount should not be too large each time, and the time interval between two times should not be less than 15 minutes, in order to observe the working tendency of the system.Once the expansion valve is adjusted, do not move it unless the working conditions are greatly

3.4Capturing Liquid

Close the outlet valve of the water condenser first, start the compressor, open the plate cooling solenoid valve and the condensing solenoid valve after 10s, and run the compressor for 5 to 8 minutes, check the medium pressure of the compressor, stop the compressor when the intermediate pressure is about 0 kgf/cm, and at the same time close the liquid inlet valve of the water condenser, Freon will receive liquid into the water condenser.

3.5 Replace cleaning filter

It is recommended to replace the cooling system after using it for more than 1 year Filter elements for filter drier and filter elements for return air filter. It is best to replace it once a year. If it cannot be replaced, it should be removed and cleaned with gasoline.

3.6 Change coolant

3.6.1 Use of cooling oil

In general, the cooling oil should be changed after the cooling system has been running for 100 hours, and the cooling oil should be changed after another 10,000-12,000 hours of operation The bit exposes 1/ of the sight glass4 is enough, do not add more, too much oil can easily cause oil shock. In general, special refrigeration oil should be used in accordance with the manufacturer\'s requirements.

3.6.2 Cooling oil replacement

(1) Toggle the compressor suction off Air valve, manually reset the oil pressure safety regulator, start the compressor, let the refrigerant in the compressor run into the system, and when the pressure in the compressor is balanced with the atmospheric pressure, turn off the compressor (cut off the power supply ), and turn off the compressor to aspirate. At this time, the pressure in the compressor will rise slightly, open the connection on the outlet valve and release the air.

(2) Unscrew the oil drain plug from the compressor oil drain port, remove the oil filter and drain the dirty oil.

(3) Clean the metal powder on the oil plug of the oil filter with gasoline, put it back after drying, and tighten the oil drain plug.

4) Unscrew the screw plug on the top left of the oil sight glass of the compressor, connect the oil-filled pipe to the oil drum, and evacuate the compressor, and the cooled oil will be automatically sucked into the compressor due to the effect of atmospheric pressure.

(5) The amount of oil change only needs 1/4 of the oil sight glass of the compressor, then screw on the plug.

(6) Use a vacuum pump to remove the air from the compressor.

(7) Open the suction and discharge valves of the compressor to start the compressor.

3.7 Exhausting the air from the cooling system

Close the liquid outlet valve of the water condenser, start the compressor, open the plate cooling valve and condensing valve after 10s, and turn off the compressor after 5 minutes of continuous machine operation, let the refrigerant after 10 minutes to cool to liquid and all the air is in the liquidAbove, through the liquid inlet valve of the water condenser, unscrew the nut next to it and turn the valve stem clockwise to exhaust the air.

3.8 Compressor fluid hammer issue

Liquid refrigerant or gas aspirated lubricating oil in the compressor cylinder will damage the suction valve. Liquid hammer can cause damage to valve plates, pistons, connecting rods, crankshafts and gudgeon pins in a short time. Due to the ingress of liquid in the cylinder can reduce or prevent liquid hammer.The most commonphenomenon of liquid hammer is suction valve plate breaking and connecting rod breaking.

The main types of fluids that cause compressor fluid hammer are the following:

(1) Liquid return, that is, the liquid refrigerant or lubricating oil thatflows back from the evaporator to the compressor;

(2) Foam when starting with liquid ;

(3) There is too much lubricating oil in the compressor