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The commonly used air compressors on ships are composed of various ship air compressor parts, including crankcase, cylinder block, cylinder head, crankshaft, connecting rod, piston, sealing device, air cooler, oil-water separator, gear oil pump, oil filter, oil cooler, vortex water pump, and others.
During the operation of a ship air compressor, various failures often occur, such as valve leakage, high frequency of piston ring replacements, cylinder inner diameter wear, connecting rod lower head bearing wear, and overpressure at various stages, which directly affect the normal operation of the air compressor equipment.
To avoid impacting the normal operation of the equipment, and apart from rationally scheduling preventive maintenance, one should also understand the technical requirements for the normal operation of various ship air compressor parts. Proper maintenance and servicing of ship air compressor parts can extend the machinery's operating cycles, reduce repair times, and improve work efficiency. This article will provide a detailed introduction to the maintenance of several ship air compressor parts.
The valve plate does not receive much impact energy during each opening and closing, but the frequency of these actions is high.
Usually, the decision to dismantle the valve is based on changes in pressure or temperature changes on the valve cover.
Valve failures should be comprehensively judged based on temperature, pressure, and sound. Higher intake and exhaust pressure at the previous stage should prompt checking the intake and exhaust valves at the subsequent stage.
Temperature
If the intake valve of the second stage is not tightly closed, the compressed gas in the cylinder will leak into the second stage intake pipeline, raising the intake temperature, noticeable by feeling the second stage intake valve cover.
If the exhaust valve of the second stage is not tightly closed, high-pressure gas will flow back into the cylinder, raising the exhaust temperature since the backflow gas is not cooled effectively.
Pressure
If the intake valve of the second stage is not tightly closed, high-pressure gas in the cylinder will leak into the intake pipeline, raising the intake pressure and lowering the exhaust pressure.
Similarly, if the exhaust valve of the second stage is not tightly closed, high-pressure gas in the exhaust pipeline will flow back into the cylinder, lowering the exhaust pressure and increasing the intake pressure.
Valve repair includes the repair or replacement of the valve seat and valve plate.
Grinding of Valve Seat and Valve Plate
During the grinding of valve seat and valve plate, force should be applied evenly, and the grinding paste should be fine.
Valve plates typically use a figure-eight or simulated figure-eight grinding motion to ensure uniform contact between the grinding surfaces, improving grinding quality and maintaining consistent wear of the grinding tool.
Valve Replacement
During disassembly, use a special tool for the cover, insert a wrench rod into the tool hole, add a sleeve, stabilize the tool, and rotate the sleeve parallel, applying sudden force until hearing a sound indicating the cover is loose, then unscrew the cover.
Then, insert the special valve tool into the valve slot, screw on the guide ring, insert the wrench rod into the tool hole, and rotate the wrench rod parallel to remove the valve, adding a sleeve if necessary.
During assembly, follow the reverse order, ensuring that the copper gaskets are annealed before use.
Checking Valve Sealing
Check the sealing of both repaired and new valves. First, clean with diesel oil, then use kerosene leakage test by filling the valve with kerosene. If no more than three drops leak within two minutes, the sealing is qualified.
After ensuring the seal quality, blow out each stage step-by-step and install each stage sequentially.
Regularly clean the intake and exhaust valves
When installing the valves, blow out each air chamber sequentially to prevent dust and mechanical impurities from entering the cylinder.
Closely monitor the usage of piston rings at all stages, and replace them immediately upon noticing damage
Replacement should be planned, and care should be taken to keep the cylinder clean.
Ensure the axial clearance and opening gap during piston ring assembly to prevent excessive dry friction due to high gas temperature expansion of the piston ring within the cylinder.
Regularly clean the coolers, oil-water separators, and pipelines at all stages
This prevents rust and carbon deposits from clogging the drainage outlet of the oil-water separator, ensuring that condensed water is discharged timely rather than entering the cylinder.
It also improves heat exchange efficiency and significantly prevents rust and carbon deposits from entering the cylinder, reducing cylinder wear.
Cylinder Inspection
First, clean the inside and outside of the cylinder, and inspect carefully with the naked eye or a magnifying glass for scoring and scratches, estimating the distribution area, severity, and location of the faults.
Cylinder Repair
For minor scores on the working surface of the cylinder, use fine honing stones or fine sandpaper for grinding. Grind around the cylinder's perimeter, and after finishing, use cotton or a brush dipped in 25% nitric acid solution to erode the ground areas for about five minutes, then wash with clean water and neutralize with a 10% to 15% sodium chloride solution before oiling.
The crankshaft is one of the most important parts of a ship air compressor.
Its working conditions are complex, with the crankshaft journal subjected to gas pressure, centrifugal force from the big end of the connecting rod, and reciprocating inertia force from the piston connecting rod mechanism. These unequal and varying forces during a working cycle cause elastic deformation of the crankshaft. Poor oil quality can cause scoring and corrosion of the crankshaft journal.
Repairing scored and corroded crankshaft journals can be done with an oil file. During filing, ensure the file does not change direction to avoid shaping the journal into a polygon. After filing, polish the journal to improve smoothness.
Method
Tear fine sandpaper to the width of the journal, dip in lubricating oil, wrap with a rope, pull and grind, and then polish with canvas to the desired level.
During the operation of the air compressor, the connecting rod continuously experiences alternating tensile and compressive loads from gas pressure and inertia force, leading to bearing wear on the upper and lower heads of the connecting rod and damage to the connecting rod bolts.
Repair of Wear on the Lower Head Bearing of the Connecting Rod
Use a coloring method to check wear and the contact area between the lower bearing of the connecting rod and the crankshaft journal. The contact area should be at least 60%. If not, scrape accordingly. The scraping principle is “heavy color, scrape heavily; light color, scrape lightly; scrape heavily, leave lightly; scrape large, leave small.” After scraping, measure the clearance between the lower bearing and the crankshaft journal, which should not exceed 0.12mm. If it exceeds, replace the bearing bush. The clearance after replacement should be 0.03mm to 0.09mm, and conduct a coloring check.
Replacement of Connecting Rod Bolts
Typical damages to connecting rod bolts include thread stripping, biting, elongation or necking of the bolt, surface cracks, bolt bending, and rounding of the hexagonal edges of the nut, all of which necessitate replacement.
During replacement, replace both the bolt and nut as a pair. Ensure the new connecting rod bolts and nuts are clean. Tighten the nut by hand fully, ensuring there is no sticking or loosening.
When replacing, do not arbitrarily swap the bolts with the holes they fit into, as they are transition fits, gently tapped in with a soft-headed hammer. Random swaps may cause too loose or too tight fits, affecting performance.
Despite its small size, the connecting rod bolt is particularly important. Failure of the connecting rod bolt can lead to severe air compressor accidents, so meticulous inspection is necessary during maintenance and management.