Compressor bodies are normally of close grained castings of iron or steel. Modern valves are of the reed or disc type mounted in the head and are of high grade steel on stainless steel seats with a usual lift of about 2mm. Connecting rods are aluminium with steel backed white metal big ends. The crankshaft

The pistons are made from cast iron in older units, and of aluminium alloy more recently. The piston is attached to the crankshaft by con rod in the normal manner. It should be noted that the crankcase is full of refrigerant gas at suction pressure.

Liners are made from high tensile cast iron. Lubrication is generally splash only for smaller compressors with a crankshaft driven gear pump supplying bearings on larger machines.It is important to understand that actual pumped lube oil pressure is the indicated pressure less this crankcase pressure.

The properties of the Lubricating oil used in are compressors are critical and specific to the refrigerant gas used. The properties of this oil will be dealt with in the tribology section.

By the nature of the system a possibility exists whereby liquid may be passed to the compressor suction. To prevent serious damage, some form of unloading device is normally fitted. In this case the suction valve assembly is held on the liner by a heavy gauge spring. In the event of liquid passing to the compressor the suction valve will lift against this spring.

Note:
Should water enter the system, acids may be formed by the reaction with the refrigerant gas. This is especially true for freon systems. These acids attack the copper in the system- typically the pipework- and allow it to be transported through the system. It is not uncommon to find this deposited on the suction valve plate. More troublesome is when the deposit finds its way to the crankcase seal destroying the running face.
Thus the importance of maintaining filter dryers in good condition can be seen. These should be changed at least on a schedule determined by the ships planned maintenance system. In addition to this it is common to have liquid line flow bullseye which incorporate a water detection element. Blockage of the filter dryer can be gauged by feeling the filter. If it is cooler than the surrounding pipework then the gas is being throttled through it.

Although not considered good practice in an emergency I have 'dried' the filter drier element in the galley oven although this practice is not recommended.

• Oil Return Sight Glass For Screw Compressor - 2012-11-23 - 03:54:45
• Preparation and check before commissioning for screw compressor - 2012-11-23 - 03:27:12
• Stop compressor operation - 2012-11-22 - 09:34:51
• Start she compressor by manual operation - 2012-11-22 - 09:25:23
• Short term maintenance for screw compressor - 2012-11-22 - 06:53:11
• Unloader Slide Valve for screw compressor - 2012-11-22 - 03:39:04
• Cleaning suction strainer for screw compressor - 2012-11-22 - 03:24:47
• Suction strainer for screw compressor - 2012-11-22 - 02:42:04
• Screw Compound Compressor - 2012-11-21 - 09:08:08
• Initial Oil Charge Before Starting Up Compressor - 2012-11-21 - 04:39:03

• < Prev
• Next >