Preventing Low Loads; General; Risks Of Low Load Operation; Best Practices - Atlas Copco XAHS 146 Dd S3B APP Instruction Manual

PREVENTING LOW LOADS

GENERAL

All engine parts are designed with tolerances to allow
work under full load conditions. When operating at
low load, these tolerances allow more lube oil to pass
between valve guides. stems, liners and pistons due to
the lower engine temperatures.
Lower combustion pressure has an influence on the
piston ring operation and
temperature. Low boost pressure will cause oil
leakage over the turbo shaft seal.

RISKS OF LOW LOAD OPERATION

• Cylinder glazing: the cylinder bore troughs
become filled with lacquer, displacing oil and thus
preventing correct ring lubrication.
• Bore polishing: the bore surface becomes
polished, all peaks and most troughs become worn
away, also preventing correct ring lubrication.
• Heavy carbon build up: on pistons, piston ring
grooves, valves and turbo charger. Carbon build
up on pistons can cause seizure when later
operating at full load.
• High oil consumption: prolonged no-load/low
load operation of the engine may cause it to blue/
grey smoke at low rpm with an associated increase
in oil consumption.
• Low combustion temperature: this will result in
insufficiently burned fuel, which will cause
diluting of the lube oil. Also, unburned fuel and
lube oil can enter the exhaust manifold and
eventually leak out through joints in the exhaust
manifold.
• Risk for fire.
• Soot load increase: Low loads cause the exhaust
temperatures to drop resulting in inadequate
regeneration of the diesel particulate filter. This
will increase the soot load of the filter which can
eventually lead up to a required stationary
regeneration (see section Exhaust gas
treatment).
the combustion

BEST PRACTICES

Reduce low load periods to a minimum. This should
be achieved by adequately sizing the unit for the
application.
It is recommended that a unit is always used with a
load >30% of nominal. Actions should be taken if due
to circumstances this minimum load capacity cannot
be obtained.
Operate the unit at full load capacity after any low
load operating period.
• Connect an air hose to the air outlet valve in such
a way that the compressed air can flow into the
open air without creating any danger.
• Start the unit and let it warm-up for a few minutes.
• Let the unit to run for 1 hour in full load condition.
The interval between full load capacity test runs may
vary according to the conditions on site. However, a
rule of thumb is to perform a full load capacity test
run after every maintenance operation.
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If the compressor is installed as a stand-by unit, then
it should be operated at full load for at least 4 hrs./
year. If periodic tests are performed on a regular basis
without load, these should not exceed 10 min.
Full load test runs help to clean out the carbon
deposits in the engine and exhaust system and
evaluate the engine's performance. To avoid potential
problems during a test run the load should be
gradually increased.
In rental applications (where load is often an
unknown factor) units should be tested at full load
after each rental job or every 6 months, whichever
comes first.
For more info, please contact your Atlas
Copco Service Center.
Please note that when a failure occurs and is deemed
due to low load operation, repair is not covered by
warranty!