System airtightness test is to check the leak. Available pressure leakage test, vacuum leakage test and charge a small amount of refrigerant leakage test of the three procedures.
1. Pressure leakage test
Pressure leakage test and blowing the same, can also be used with nitrogen, dry compressed air or ordinary compressed air. When nitrogen is used, a pressure reducing valve should be installed between the nitrogen bottle and the system, as shown in Figure 4-4. If an air compressor is used, a two-stage machine is used. The test pressure of the system is generally 1.2 MPa for low-pressure systems and 1.8 MPa for high-pressure systems. after pressurization, check the connections between pipes and between pipes and equipment with soapy water; if bubbles appear, they indicate leakage. Check no leakage, can be pressure preservation, pressure preservation time is 24h, the first 6 hours allow pressure drop 0.02-0.03 MPa, after 18 h, the temperature is constant, the pressure is unchanged for qualified.
Safety measures to be taken during the pressure test are:
(1) When compressor is used to compress air, the exhaust temperature shall not exceed 120 ℃, and the oil pressure is not higher than 0.3 MPa.
(2) The difference between the compressor inlet and exhaust pressures shall not be permitted to exceed the limited working conditions of 1.4 MPa.
(3) It is not permitted to shut down the safety valves of the machines and equipment. safety valve. High-pressure system pressure test, the low-pressure system can be separated from the high-pressure system to prevent the low-pressure system pressure is too high, the safety valve open.
(4) The control valves of oil pumps and other related equipment should be closed during the system pressure test to avoid damage.
Pressure test is the entire refrigeration system is filled with a certain pressure of nitrogen or air, so that the inner wall of the pipe wall equipment under pressure, in order to check whether the installation of the joints, flanges, tubes, equipment, etc., whether there is leakage. In the Freon system, because of fluorine on the system water content requirements are very strict, so the pressure test, more industrial nitrogen. Nitrogen has the advantages of non-corrosive, non-moisture, non-flammable and non-explosive, inexpensive and easy to operate. Try not to use compressed air, because it contains water and impurities.
Strictly prohibit the use of oxygen pressure, because of the danger, in the absence of nitrogen, can also use dry compressed air leakage test.
2. Vacuum leakage test
After the completion of the pressure leakage test, vacuum leakage test can be carried out. There are two purposes, one is to check the system in the vacuum conditions of the sealing, the second is to remove the residual gas and moisture in the system.
From the working principle of the refrigeration machine can be seen, the refrigerant in the refrigeration system circulating flow, its state is in constant change, compression for the gas, condensation into liquid, evaporation and then into gas. But belongs to the non-condensable air or nitrogen, at room temperature or in the general low temperature is not condensed to liquid. This part of the non-condensable gas exists in the cold skeptic and takes up part of the volume, thus affecting the ability of the condenser to dissipate heat, so that the condensing pressure rises, affecting the normal cooling effect. Therefore, it is necessary to pump out the non-condensable gases in the system. According to the relevant regulations: when conducting vacuum test, the pressure in the Freon system should be reduced to below 5.33KPa (i.e., the vacuum degree should be above 96kPa), and the pressure should not rise more than 1.33 kPa within 8h. The requirement of the vacuum degree should be different with the atmospheric pressure of different places. Generally speaking, the local atmospheric pressure of the day multiplied by a factor of 0.96 is the required vacuum.
Vacuum pump should be used for vacuum leakage test. For small refrigeration system or no vacuum pump, can also use the refrigeration compressor itself to vacuum.
System evacuation
(1) Close the discharge valve and open the multi-channel or evacuation valve on the discharge valve to discharge air.
(2) Close the valves in the system that are open to the atmosphere (e.g., charge valve, air release valve, etc.) and open all other valves in the system.
(3) Drain the cooling water from the condenser, otherwise the water in the system will not evaporate easily due to the low temperature of the cooling water and will be difficult to be pushed out.
(4)Force the contacts of the oil pressure relay to be normally open, and then start the compressor and stop it immediately to check whether the direction of rotation is correct and whether there is any exhaust in the evacuation orifice, and then start the compressor formally to evacuate.
Vacuuming the compressor suction valve can not be opened, especially large refrigeration compressor, otherwise the exhaust port is too late to exhaust, there is the possibility of breaking the valve. Vacuuming should be divided into several intermittent, because the suction is too fast, the accumulation of water and air in the system is not easy to be pumped out at once.
(5)After vacuuming, close the evacuation orifice first, and then shut down to prevent air backflow after shutting down due to the non-closure of the valve piece.
In the process of using the refrigeration compressor evacuation, if the compressor itself with a lubricating oil pump, with the increase in vacuum in the system will make the lubricating oil pump working conditions deteriorate, causing damage to the moving parts of the machine. So when the oil pressure (refers to the differential pressure) is less than 26.7kPa resistant, should stop immediately.
In order to check whether the system has been pumped out of water, air, etc., can be in the compressor discharge valve on the multi-purpose orifice to connect a temporary pipe, to be a large amount of air discharged from the system, the other end of the pipe into a container containing refrigerant oil. If there is still water, air, etc. in the system, the oil will appear bubbles, has to be pumped until in a longer period of time does not appear bubbles, indicating that the water, air, etc. in the system has been pumped out.
When vacuuming with a vacuum pump, you should first open the system valves, close the valves connected to the atmosphere, and connect the vacuum pump to the system refrigerant charging port. Vacuum pump pumping system air, the absolute pressure of 97.3 kPa (vacuum degree of 730 mmHg), close the system and the vacuum pump connection valve and stop the vacuum pump work, and then leak detection. The method is to use a lit cigarette near the place where the leakage point may appear, if there is a suction phenomenon, it indicates that the leakage here.
3. Charge a small amount of refrigerant leakage test
To the refrigeration system charged with a small amount of refrigerant, you can use the halogen leak detector leakage test, you can also use the test paper and soapy water and other methods of leakage detection.
4. Tap the power to check the motor steering
After the completion of the leakage test work in the unit, for the open unit, you can remove the coupling screws and pressure plate, remove the drive core, move the flywheel to the motor side, so that the motor and the compressor are separated, and then tap the way to power, check the direction of rotation of the motor is correct (for the semi-enclosed or fully enclosed unit, this work can not be done at the same time). At the same time, move the oil pump and check whether the direction of rotation of the oil pump is the same as the direction of the arrow marked on the pump casing. After passing the inspection, install the drive core and pressure plate on the coupling and fasten them with screws.