Reciprocating compressor
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A reciprocating air compressor is a compressor that uses pistons driven by a crankshaft. It is used for delivering small quantity of air at high pressure.
Air or a refrigerant such as ammonia [NH3] or Freon passes through the intake manifold [suction side], then through the compression cylinder where it gets compressed by a piston being driven in reciprocating manner via a crankshaft, and is then sent out through a discharge manifold into the upstream refrigeration system if it's a refrigeration reciprocating compressor.
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Maintenance
To keep the air compressors operating efficiently at all times, one must know what common troubles may occur and their causes. The knowledge of the air intakes; air valves; of air cylinders and pistons; and how to adjust bearings, wrist pins, and couplings is mandatory. One must be able to maintain, troubleshoot, and repair the lubrication, cooling, control, and air systems.
Air intakes
A supply of clean, cool, dry air is essential to the satisfactory operation of compressors. To ensure this, the air intake filters must be regularly inspected and cleaned; otherwise, the filter becomes clogged and causes loss of capacity. A clogged air intake screen or filter may also cause a compressor to draw oil from its own crankcase, around rings, or through oil seals, resulting in an explosion. Remove the filter element and clean it with a jet of hot water or steam, or plunge it into a strong solution of sal soda. The filter body should be drained and replaced. If the filter is the oil-wetted type, dip it in clean, medium-grade oil and allow it to drain thoroughly before replacing the filter in the intake. Do not use gasoline or kerosene for cleaning filters! The fumes may collect and explode in the compressor or receiver. Take care to prevent entrance of rain or spray into intake pipes, and provide a means for draining the intake pipe (KIR) of any water that may collect. The lines should be as short and direct as possible.. Also prevent any possible intake of fumes coming from fuel tank vents, spilled oil, or gasoline.Air valves
Air inlet and discharge valves must be kept clean and in good working order. Leaky valves are generally dirty valves, and they cause capacity loss. The valves are removed by first loosening their setscrews or clamps, and then removing their cover plates. Each valve may then be lifted out. Each valve should be marked to make certain that it is returned to the same port from which it was removed. Valves removed for inspection should not be taken apart for cleaning unless their conditions make it necessary. Dirt or carbon in valve ports can usually be removed without taking the valve apart. This is done by soaking the valves in kerosene, and then giving them a stiff brushing or a light scraping. Valve action should be tested by inserting a screwdriver through the seat ports; the valve should lift and close freely. If it becomes necessary to disassemble the valve, note the arrangement of the various parts so that the proper relationship will be kept when the valve is reassembled. Before replacing air valves in a cylinder, inspect the gaskets and replace any that are damaged. Copper-covered asbestos or plain, thin copper gaskets should be used. If these are not available, 1/16-inch compressed-asbestos sheet gaskets may be used temporarily. Each valve assembly should be inserted in the same hole from which it was removed. Since it may be difficult, in many cases, to distinguish between suction or discharge valves, extreme care must be taken when the valves are being inserted in the cylinder. Make certain that suction valves open TOWARD, and the discharge valves AWAY FROM, the center of the cylinder; otherwise, serious damage or loss of capacity will result.Cylinders and pistons
The cylinders on pistons should be inspected only AFTER the manufacturer’s technical manual has been consulted. Be careful when removing heads, particularly where metal-to-metal joints are involved, to prevent damage to the joint. If replacement of piston rings is required because they are worn or broken, take accurate measurements of the cylinder liners. The liner may also need to be replaced if it is badly worn or out of round. The side clearance of the rings should be such that the rings will fall easily into the piston grooves, which should be deep enough for the ring thickness. Ring splits should be staggered. After assembling the piston, wire the rings tight with a soft copper wire so that they will enter the bore easily. This wire can be removed through the valve ports after the ring has started into the cylinder bore. When reassembling the air cylinders and heads, be sure they are all drawn down evenly, especially on multistage compressors where the heads contain cylinders for third and fourth stages. Otherwise, the result will be excess wear on the cylinders and pistons. When a compressor piston has been replaced, the piston end clearance must be checked. This is done by inserting a lead wire through a valve port or indicator connection. Jack the compressor over. When the piston has moved to the end of its stroke, the lead will be flattened to the exact amount of clearance. The wire should be long enough to permit a reading near the center of the piston. These readings should be taken after any adjustment or replacement of the main, crank pin, wrist pin, or crosshead bearings. Methods of adjusting the clearances vary according to the compressor design. MUST consult the manufacturer’s instructions for suggested adjustment.Miscellaneous adjustments
From time to time other miscellaneous adjustments are required on compressors, including those pertaining to wrist pins, crosshead shoes, reduction gears, couplings, and V-belt drives. The manufacturer’s technical manual gives specific information for the care, adjustment, and replacement of all fitted bearings. Refer to the manufacturer’s instructions for detailed information on when and how to make these adjustments. Wrist pin bushings are replaced when necessary. This is done when they are worn to the point of becoming noisy. Wear should be slight, but adjustment should be made when the travel of the piston rod causes a movement in the stuffing boxes. Alignment of reduction gears and pinions should be checked periodically, especially on a new compressor. Flexible couplings require very little maintenance when they are properly lined up. Some types require occasional lubrication to prevent excessive wear of springs and bushings. A noisy coupling is an indication that the bushing is worn and requires replacement. V-belt drives require adjustment for belt tension. Belts generally stretch slightly during the first few months of use. A loose belt will slip on the motor pulley and cause undue heating and wear on the belt. A tight belt will overload the bearings. Belts should be protected against oil and high temperatures. To prevent rapid deterioration, belts should not be used at temperatures above 130°F (54.4°C). V-belts are usually installed in sets of two or three. If a single belt is worn or deteriorated, the complete set should be replaced to ensure that each belt will carry its share of the load.Lubrication system
Proper care of a compressor lubrication system includes the following: Keep the oil at a normal level in the reservoir at all times to maintain proper oil temperature. - Change crankcase oil periodically, and at the same time clean and flush the crankcase and clean the oil filter. -Maintain proper lube-oil pressure by keeping the oil pump in good working order and adjusting the bypass relief valve Keep the oil cooler free from leaks (since pressure on the water side exceeds that of the oil) to prevent oil contamination and emulsification. - Properly adjust the lubricator for the specified quantity of oil feed.Cooling system
Proper care of a compressor cooling system includes the following inspections and maintenance procedures: - Periodically inspect the intercoolers and aftercoolers. - Remove collections of gummy oils or tarry substances from the cooler tubes and drying them thoroughly before reassembling. - Correct any leakage in tube nests to prevent leaks of water into the compressor while secured or leaks of air into the water side during operation. - Inspect and clean the cylinder water jackets periodically with a cleaning nozzle. When filling the cooling water system after the compressor has been drained, open the water inlet slightly to allow the water to rise slowly in the cooler shells and water jackets. Vent valves fitted to the water spaces should be opened to permit entrapped air to escape and to remove any air pockets.
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