Page 12 - Climalife_Contact_15_EN

12 | PROCESS | February 2019 | Climalife contact #15
PROCESS
Choosing the right lubricant
and performing regular maintenance can prevent compressor damage: expert from HRS explains
Founded in 1945, HRS (Hermetic Réfrigération Service) specialise in rebuilding all brands of refrigeration compressors for the European market.
Across more than 8,000 m2 of work- shop and office space, HRS give a new lease of life to refrigeration compressors. The company has
a lot of expertise which enables it to support and advise its customers in the prevention, analysis and repair of broken compressors. HRS not only rebuilds compressors, but can also, through detailed examination of the disassembled compressor and discussions with refrigeration engineers, find the causes of degradation and thus help its customers to better prevent damage.
The cause of damage and lubrication defects
A compressor is the vital organ of a refrigeration system; the longevity of which depends on its maintenance, the condition of the cooling circuit and its components. Generally able to operate for more than 50,000 hours, in the event of a breakdown, it becomes witness to the source of the breakdown, and makes it easier to diagnose the source of the problem. HRS add that there are five main types of incidents that classify and identify deterioration of a compressor, bearing in mind that this deterioration can be the result of other incidents:
- Presence of contaminants in the refrigerant circuit.
- Overheating.
- Surges of liquid or oil.
- Breakage due to lack of lubrication. - Electrical incidents.
HRS explains that in more than 80% of instances, a compressor is damaged as a result of anom- alies in the system or operation under critical conditions. It is estimated that 70-75% of the damage is caused by lubrication problems.
Lubrication defects: This is often the first cause of compressor failure and is often only a symptom of a circuit related problem, but it can lead to significant mechanical damage. Surrounding factors that concern the com- pressor will most often be called into question (eg pressure regulators, under-performing heat exchangers, evaporator leakage, etc.) as Marc Beaurain, Technical Director at HRS points out.
Failures such as jamming, snapping at the connecting rods, bearing rings and crankshaft are recurring damage that HRS has seen on compressors received and rebuilt in their workshops.
When dismantling and examining compressors, HRS is able to identify the cause of the problem: scratches on deteriorated parts, appearance and colour of the oil or parts are indicators of why a compressor failed.
Lack of oil, excessive oil temperature, drop in viscosity or the migration of refrigerant into the oil, are several reasons why there may be a lack of lubrication.
As oil is essential for the lubrication and cooling of moving parts in the compressor, it is nec- essary that its level in the housing remains the same. A drop in oil level or poor return of oil to the compressor may cause overheating of the compressor parts and therefore damage it. A refrigerant leak and therefore a lack of charge, will cause overheating of the compressor and cause a drop in oil viscosity. This may cause the oil film to separate and not lubricate the moving parts. Although not the only one, it is the most common reason for compressor overheating. Incorrect adjustments will also cause the moving parts to heat up and will degrade the viscosity of the oil, which will be too fluid to avoid mechanical destruction. There will also be phenomena related to the migration of the refrigerant into the oil, which returns to the compressor in the liquid phase, cleans and dries the moving parts of the compressor which should remain lubricated.
Presence of contaminants: water vapour is the number one enemy of the refrigerant circuit. It causes direct contamination by sludge and oxide formation. Water breaks down the refrigerant by chemical reaction, with the formation of acidity rapidly weakening the winding insulation.
At high discharge temperatures, the reaction between the oxides of the oil and the refrigerant will cause copper plating. With water vapour, ice plug formation will form on the suction filters of the compressor. There may also be contamination by air or impurities that will have negative but slower impact than water vapour.
Stéphanie Raguet-Gérardin, Key Account Manager at Climalife and Marc Beaurain, Technical Director at HRS.
Overheating: a compressor overheating prob- lem is usually caused by a low mass flow at the suction side of the compressor. This may be due to abnormal suction, overheating, or a lack of refrigerant charge, but also to a very high compression ratio or prolonged operation at more than 50% power reduction of compressor capacity. If it overheats, the lubricity of the oil will be greatly altered which could damage the connecting rods and bearing rings.
Surges of liquid or oil: are mainly the result of pressure regulator malfunction. Oil surges can be caused by prolonged power reduction below 50% of the compressor capacity. As the speed of the gas is not sufficient, the oil will remain trapped in the evaporator and then return suddenly as soon as the compressor gets back to 100%. This can lead to a failure at the cylinder joints, discharge and/or suction valves, breaking rods and pistons, etc.