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Some oil carryover from the air compressor into the air brake

system occurs as a normal part of all air compressor operation. Compressors require oil carry over to lubricate the compressor's valves and rings. It is typical to find some presence of oil at the inlet and discharge ports of the air compressor. oil present at the exhaust of unloader valves and is dryers is normal and indicates that these

components are functioning properly, removing contaminants from the system.

Vehicles equipped with a desiccant type air dyer that incorporates an air filter (separator) for removing oil from the air will normally minimise oil passed through the reservoir. The oil collects in the air dryer with condensed moisture and is periodically purged.

Often, the routing or location of the air dryer exhaust port can amplify concerns about oil passing, depending on where the purges oil / water mixture is expelled on the vehicle, e.g. on a fender or onto a fuel tank. This can mistakenly be identified as a "problem" oil passing, when in actuality the air dryer and compressor are functioning properly.

Is the ratio of time the compressor spends building air to the total engine running time. Air compressors are designed to build air (run "loaded") up

to 25% of the time.

Higher duty cycles cause conditions such as excessive heat, that affect compressor performance and longevity which will require additional maintenance.

Factors that add to the duty cycle are; inter-link trailers, under sized compressor, air suspension, addition air accessories, excessive stroke on brake chambers, frequent stops, excessive leakage from fittings, connections, lines, brake chambers, valves etc.

Compressors that normally get their air intake before the turbo charger, will pump excessive oil if the engine air filter is restricted, this restriction causes an excessive vacuum at the compressor inlet, this vacuum will draw oil past the rings. 25 inches of water is the maximum restriction allowable.

Broken or worn intake pipe, (unseen by many, as the worn section of the pipe is normally up against the causing object) will allow unfiltered air induction to the compressor.

Operating the compressor with unfiltered intake air results in excessive wear to the pistons, rings and cylinder bones in a relatively short period of time.

Allows the air, wator-vapor and oil vapor mixture to cool between the

compressor and the air dryer. The typical size of a vehicle's discharge line, is determined by vehicle manufacturers assumption that a compressor has a normal (less then 25%) duty cycle, operating in a tempreture climate.

When the tempreture of the compressed air that enters the air dryer is within the normal range which is 95*C at air dryer fitting loaded, the air dryer can remove most of the charging system oil.

If the tempreture of the compressed air is above the normal range caused by excessive DUTY CYCLE, oil as oil-vapor is able to pass through the air dryer and into the air system. Excessive heat also allows the minuscule amount of oil-vapor that is passed naturally by the compressor to turn to carbon, this carbons ever increasing restriction has a snowball effect that will cause the compressor to fail prematurely, from excessive pressure and ever increasing tempreture, 104*C max at coolant fitting, this is also the case with kinked delivery pipes.

Larger diameter discharge lines and fittings will help reduce the tempreture and in turn oil carryover and carbon. Max tempreture at delivery fitting 183*C loaded.

This can be in the form of wither governer valve / air dyer / unloader valve, if any of these are faulty they will affect the loading and unloading of the compressor causing excessive air pressure or duty cycle, which in turn increases delivery pipe tempreture. SEE heading delivery pipe.

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(+27) 11-609-2030


15 Betschana Road, Sebenza, Edenvale, South Africa