After the refrigeration equipment is installed, welding slag, iron filings, oxides, sand, etc. still inevitably remain in the system. In order not to damage the valve and the unit, and to prevent the filter and pipeline from being blocked, the sewage must be discharged before the unit runs. . Sewage discharge usually uses pressure gas to blow out the pipes and systems. The blow-off pressure is 0.6MPa. Blow-off work can use compressors, air compressors, nitrogen bottles, etc. as the gas source. For a Freon system, the blowing off work is best performed with nitrogen, because Freon requires high water content in the system, and compressed air will inevitably bring in moisture. And nitrogen is non-corrosive, non-moisture, non-combustible and non-explosive, low price and convenient operation.

Sewage discharge work can be divided into sections and floors. Sewage outlets should be set at the lowest point of each section. During the blowdown, all the valves of the system that are exposed to the outside atmosphere are closed, and the remaining valves are fully open. A cork can be used to plug the mouth of the blow-out pipe section at the sewage outlet (for safety reasons, the cork is fastened with iron wire or the sack is used to secure the cork to prevent the cork from flying out and hurting people). When the pressure reaches o. 6 MPa, the wooden plug is knocked off, and the gas is quickly discharged to discharge the dirt and moisture in the pipeline. This is repeated one to three times until the dirt and moisture are removed. Sewage discharge work should be carried out in a sequential manner until it is all cleared.

The method of checking the blowdown is as follows: When outgassing, place a wet white gauze or a dry white paint board at 150-200mm of the blowdown outlet. If there is no obvious stain after the gas blows, it is qualified. During the drainage process, the valve should be opened and closed as little as possible to prevent dirt from damaging the sealing line of the valve. After draining the system, the valve core of the filter and valve should be removed and cleaned.