Insufficient Displacement

Insufficient displacement is one of the most common faults of compressors, mainly caused by the following reasons:

1. Fault of the intake air filter: Fouling and clogging reduce the displacement; an excessively long suction pipe with an undersized diameter increases suction resistance and affects air volume. The filter should be cleaned regularly.
2. Reduced compressor speed leading to lower displacement: Improper operation of the air compressor. Since the displacement of an air compressor is designed for a specific altitude, intake air temperature and humidity, when operated on plateaus exceeding these standards, the suction pressure drops and the displacement will inevitably decrease.
3. Severe wear and out-of-tolerance of cylinders, pistons and piston rings, leading to increased clearances and leakage, which affect displacement. For normal wear, wearing parts such as piston rings must be replaced in a timely manner. For improper installation and inappropriate clearances, corrections shall be made according to drawings. If no drawings are available, empirical data may be adopted: for the circumferential clearance between piston and cylinder, it shall be 0.06%–0.09% of the cylinder diameter for cast iron pistons, 0.12%–0.18% for aluminum alloy pistons, and a smaller value within the aluminum alloy range for steel pistons.
4. Loose stuffing box causing air leakage and reduced air volume. This is mainly due to substandard manufacturing of the stuffing box itself, or poor centering between the piston rod and the stuffing box during installation, resulting in wear, scoring and leakage. Lubricating oil is usually injected into the stuffing box for lubrication, sealing and cooling.
5. Influence of faulty suction and discharge valves on displacement. Metal fragments or other foreign matters trapped between the valve seat and valve plate cause incomplete closing and air leakage, which not only reduces displacement but also affects interstage pressure and temperature. This may result from manufacturing defects such as warped valve plates, or severe wear of the valve seat and valve plate.
6. Poor matching between valve spring force and gas force. Excessively high spring force delays valve plate opening, while insufficient spring force causes delayed closing. This not only affects air volume but also increases power consumption, shortens the service life of valve plates and springs, and alters gas pressure and temperature.
7. Improper compression force on the air valve. Insufficient force causes leakage, while excessive force deforms or damages the valve cover. The compression force can generally be calculated by the formula:p=k⋅4π​D2P2​where D is the valve chamber diameter, P2​ is the maximum gas pressure, and k>1, usually 1.5–2.5 (1.5–2.0 for low pressure, 1.5–2.5 for high pressure). Field practice proves this range suitable. A faulty valve will cause overheating of the valve cover and abnormal pressure.

Abnormal Temperature

Abnormal discharge temperature refers to a temperature higher than the designed value. Theoretically, factors increasing discharge temperature include suction temperature, pressure ratio, and compression index (for air, k=1.4). In practice, high suction temperature can result from low efficiency of intercoolers or excessive scaling affecting heat transfer, which raises the suction temperature of subsequent stages and thus the discharge temperature. In addition, leakage from valves or piston rings not only increases discharge temperature but also changes interstage pressure; any pressure ratio above the normal value will raise discharge temperature. For water-cooled units, insufficient or interrupted water supply also causes high discharge temperature.

Abnormal Pressure

If the compressor cannot meet the required flow rate at rated pressure, the discharge pressure will drop, requiring replacement with a unit of the same discharge pressure but larger capacity. The main cause of abnormal interstage pressure is leakage from faulty valves or worn piston rings, so troubleshooting should focus on these components.

Abnormal Noise

Malfunctioning components of the compressor will produce abnormal noise, which can generally be identified by operators. Knocking in the cylinder may be caused by insufficient clearance between piston and cylinder head, loose or disengaged connecting nuts between piston rod and piston, loose plug on the piston end leading to upward impact, foreign metal fragments in the cylinder, or accumulated moisture. Knocking in the crankcase may arise from loose, disengaged or broken bolts of crankshaft bearings, connecting rods and crossheads, severe journal wear increasing clearances, or excessive clearance/wear between crosshead pin and bushing. Knocking in the valve chamber may result from broken discharge valve plates, weak or damaged valve springs, or improper adjustment of the load regulator. Faults can be diagnosed and addressed accordingly.

Overheating Fault

Overheating means the temperature at friction pairs (crosshead and slide plate, packing and piston rod, etc.) exceeds the specified limit. Consequences include accelerated wear of friction pairs and accumulated heat leading to burned friction surfaces and major equipment accidents. Causes of bearing overheating mainly include uneven contact or insufficient contact area between bearing and journal, bearing misalignment or bent crankshaft, low lubricating oil viscosity, blocked oil passages, oil supply failure due to pump faults, poor leveling and improper clearance during installation, or misalignment between main shaft and motor shaft with angular deviation.