The refrigeration system must be a clean, dry and tight closed cycle system. After the refrigeration equipment is installed or overhauled, some impurities such as welding slag, rust, scale and moisture will inevitably remain inside the system. In order to keep the system clean, prevent dirt from damaging the compressor and the valves in the system, avoid problems such as system pipeline blockage, and ensure the normal and efficient operation of the refrigeration system, the refrigeration system must be purged and discharged before the operation of the refrigeration equipment.
When the system is blowing down, all valves connected to the atmosphere should be closed tightly, and all other valves should be opened. Sewage discharge should be carried out in sections or sub-systems according to equipment and pipelines. The high-pressure system should be discharged first, and the low-pressure system should be discharged second. The sewage outlet should be selected at the lowest point of each section. Never use flammable gases such as oxygen during the sewage discharge operation, and the sewage outlet should not face the operator to ensure safety.
The ammonia refrigeration system should use 0.8MPa (gauge pressure) compressed air for blowdown, and the Freon system should use 0.5-0.6MPa (gauge pressure) nitrogen blowdown. It should be purged repeatedly, and a white identification board (such as a clean white cloth tied to a wooden board) should be set at the sewage outlet for target inspection until no dirt is discharged. In order to effectively utilize the explosive power and high-speed airflow of compressed gas, a valve can be installed at the sewage outlet, and the valve can be opened quickly when the pressure in the system rises, so that the gas can be discharged quickly and the dirt can be brought out. In practice, the cork can also be used to block the sewage outlet. When there is a certain pressure in the system, the cork will be knocked out so that the gas can be discharged quickly. The effect of this sewage discharge method is very good, but there is a certain degree of danger, so be careful and pay attention to safety when operating.
Before sewage discharge, the instruments and safety valves in the system should be protected, and the solenoid valve, check valve core and filter screen should be removed, and they can be reinstalled and reset after the vacuum test is passed. After the system is purged and cleaned, the valves that may accumulate dirt should be disassembled, cleaned and reassembled. In addition, when the refrigeration system is overhauled, it is also necessary to use nitrogen or dry compressed air to blow off the remaining oil and impurities in the system. In order to dissolve the oil and facilitate discharge, a proper amount of trichlorethylene can be poured into the system, and after the oil dissolves, it will be blown into the air. Trichlorethylene is harmful to the human body. Therefore, indoor ventilation should be paid attention to when using, and the operator should properly keep away.