Generally speaking, the operator can identify the abnormal noise of the compressor. The clearance between piston and cylinder head is too small, causing direct impact; The connecting nut between the piston rod and the piston is loose or tripped, the piston moves upward in series and collides with the cylinder head, metal fragments fall into the cylinder, and water accumulates in the cylinder, all of which can make a knocking sound in the cylinder. If the bolts, nuts, connecting rod bolts and crosshead bolts in the crankcase are loose, tripped or broken, if the shaft diameter is seriously worn, the clearance increases, and if the clearance between crosshead pin and bushing is too large or severely worn, the sound of impact can be heard in the crankcase. If the exhaust valve plate is broken, the valve spring is soft or damaged, or the load regulator is improperly adjusted, a knocking sound can be made in the valve chamber to find faults and take measures.