Jonkun nettilähteen mukaan Copelandin kompressorien keskimääräinen elinikä 13,5v.
Introduction
A frequent cause of compressor failure that is seldom recognized or understood is short cycling. If a compressor failure results, it will either be a motor burn or a lubrication failure, and in both cases it is a near certainty that the cause of failure will be misdiagnosed. Each time a compressor starts, there is a quick reduction in the suction pressure and therefore the crankcase pressure. The pressure drop causes a reduction in the saturation temperature, resulting in the oil-refrigerant mixture flashing into foam and vapor with the frequent result that a large percentage of the crankcase oil is pumped out of the compressor. If the compressor operates for sufficient time to stabilize the system, the oil will return to the compressor, but if the running period is very
short, the oil may still be trapped in the system when the compressor cycles off. If this cycle is repeated, the compressor will progressively pump oil from the crankcase, and the entire oil charge can be lost from the crankcase. If the running cycle is short, an oil pressure safety control may not be actuated since it requires at least two minutes run time to trip the heat actuated safety element. Under such conditions the compressor can operate without lubrication to the bearings, with the obvious potential for damage.
A second source of damage can result from liquid refrigerant flooding and loss of refrigerant control. Most expansion valve are quite sluggish in their control characteristics and tend to react slowly to any sudden change in system operating conditions. Under short cycling conditions, the expansion valve may be unable to reach a stable control condition and uncontrolled liquid refrigerant flooding can occur, again posing a threat to the compressor. Every time the motor cycles on or off, the stator windings try to flex and move. Under prolonged cycling or short cycling conditions, this flexing may eventually create sufficient movement in the windings to scuff the insulation and cause a short. The larger the motor, the more vulnerable it is to winding flexing. With modern motor insulation and varnishes in a properly wound motor, this failure mode is rare, but the potential threat is present in any system subjected to excessive cycling, since the probability is that any motor has a finite life in terms of the number of cycles it can endure. Short cycling can originate from many sources, and most such problems can be prevented if we understand the reasons behind them.
Tuossa puhutaan kolmesta tavasta miten kompressori päätyy hautaan.
Alle parin minuutin käynti vaahdottaa öljyn kylmäaineen sekaan ja kuljettaa sen pois voitelemasta kompressoria.
Paisunta venttiilin toiminta muuttuu niin että tulistusta ei ole enää koneessa ja nestemäinen kylmäaine pääseen koneeseen.
Käynnistykset kuormittavat suurien moottorien käämityksiä ja ne saattavat mennä oikosulkuun eristeiden petettyä. (luulisi että pehmokäynnistin pienentäisi tätä riskiä)
Sitten käyntiajoista:
5.12 Minimum run time
Emerson Climate Technologies recommends a maximum of 10 starts per hour. There is no minimum off time because scroll compressors start unloaded, even if the system has
unbalanced pressures. The most critical consideration is the minimum run time required to return oil to the compressor after start-up. To establish the minimum run time obtain a sample
compressor equipped with a sight tube (available from Emerson Climate Technologies) and install it in a system with the longest connecting lines that are approved for the system. The
minimum on time becomes the time required for oil lost during compressor start-up to return to the compressor sump and restore a minimal oil level that will ensure oil pick-up through the
crankshaft. Cycling the compressor for a shorter period than this, for instance to maintain very tight temperature control, will result in progressive loss of oil and damage to the compressor.
Danfos
Compressor Protection
Anti Short Cycle
The system must be designed in a way that guarantees a minimum compressor running time to ensure that the motor remains cool and that the oil will return satisfactorily back to the compressor.
There must be no more than 12 starts an hour. A higher number reduces the service life of the compressor. The use of an anti-short cycle timer is highly recommended. A three minute time out
between starts is recommended.
Copeland
COMPRESSOR SHORT CYCLING
AN UNRECOGNIZED PROBLEM
A frequent cause of compressor failure that is seldom recognized or understood is short cycling. If a compressor failure results, it will either be a motor burn or a lubrication failure, and in both cases it is a near certainty that the cause of failure will be misdiagnosed. Each time a compressor starts, there is a quick reduction in the suction pressure and therefore the crankcase pressure. The pressure drop causes a reduction in the saturation temperature, resulting in the oil-refrigerant mixture flashing into foam and vapor with the frequent result that a large percentage
of the crankcase oil is pumped out of the compressor. If the compressor operates for sufficient time to stabilize the system, the oil will return to the compressor, but if the running period is very short, the oil may still be trapped in the system when the compressor cycles off.
Summary
Regardless of the motor design, excessive short cycling can shorten compressor life, and the service engineer must be alert to malfunctions in system controls which can create short cycling
conditions.
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