What surging is
Surging, also called surge or pumping, is an unstable flow condition in the turbocharger compressor. When the air the compressor delivers meets more resistance than it can push against at that operating point, the flow can break down and briefly reverse, then recover, and the cycle repeats. The result is a pulsing noise from the air side and charge air pressure that swings. It is first of all a flow problem, but repeated surging loads the rotor and the bearings, so it should not be treated as a nuisance that can wait.
Signs that may point to surging
Engineers usually notice surging through a combination of observations rather than a single one:
- A repeated whooshing, banging or barking noise from the turbocharger or its air intake.
- Charge air pressure that pulses or swings on the gauge or in the alarm system.
- Turbocharger speed readings that fluctuate.
- Changes in exhaust gas temperature, or visible smoke.
- New or increased vibration at the turbocharger.
- An engine that hunts in speed or load without a clear reason.
These signs can point to surging, but they can also come from other faults, so they are a reason to look further and not a diagnosis.
Common causes on the compressor and air side
A fouled or worn compressor wheel and casing changes the way the air flows and can bring the unit closer to instability. Damaged blades have a similar effect. A clogged air filter or intake silencer, a dirty charge air cooler and restrictions in the air path after the compressor all raise the resistance the compressor works against. Because these items build up slowly, a comparison with earlier readings often shows them better than a single reading does.
Common causes on the exhaust side
The turbine and the compressor are linked, so a problem in the exhaust path can show up as a problem in the air path. Fouled or damaged turbine parts, and high resistance in the exhaust system after the turbocharger, such as a fouled exhaust gas boiler or other equipment in the exhaust line, can disturb the balance between the turbine and the compressor. Check the manufacturer's information on the readings that matter for your installation.
Operating conditions and engine factors
Surging is not always a fault in the turbocharger. Operation at very low load, sudden load changes, for example in heavy weather, and conditions outside those the turbocharger was matched to can all bring it on. Faults in the engine itself can have the same result: poor combustion, injection or fuel problems, or a cylinder that runs differently from the others change the exhaust energy that drives the turbine and the air the engine needs. When the engine is the origin, replacing turbocharger parts will not remove the cause.
What to do when you suspect surging
- Write down the load, the readings, any alarms and the time when it started.
- Follow the engine and turbocharger manufacturers' instructions and the class rules on whether and how to continue running. Do not keep running under persistent surging.
- Check the obvious items against the manual: the condition of the air filter, the pressure drop across the charge air cooler and any indication of exhaust resistance.
- Compare today's readings with earlier trends for the same load.
- Wash or clean only in the way the manufacturer describes, because an incorrect method can add damage.
- Contact a qualified specialist before the unit is dismantled, and send photos, readings and the nameplate details.
Why trend records help
A unit that surges today often showed small changes earlier: slightly lower charge air pressure for the same load, a rise in exhaust temperature, or a filter that needed attention more often. Logging the same readings at similar loads makes these changes visible and helps a specialist separate a turbocharger problem from an engine or air path problem.
Frequently asked questions
What is turbocharger surging?
Surging is an unstable airflow condition in the turbocharger compressor. The flow breaks down and recovers repeatedly, which is usually heard as pulsing noise from the air side and seen as swinging charge air pressure.
Can a dirty compressor or air cooler cause surging?
Yes, it can contribute. Fouling or wear on the compressor, a clogged air filter or a dirty charge air cooler changes the airflow the compressor has to work against. Other causes are possible, so the whole air and exhaust path should be checked.
Is it safe to keep running a surging turbocharger?
Persistent surging can load the rotor and bearings, so it should not be ignored. Follow the engine and turbocharger manufacturers' instructions, the class rules and the vessel's own procedures on whether and how to continue, and arrange an inspection.
Next step
Surging often shares its causes with other faults, so read about marine turbocharger failure causes. If vibration is part of the picture, see turbocharger rotor balancing, and if the unit has deteriorated over time, see the signs that an overhaul may be due.
If you would like a specialist to look at your unit, our Field Service covers work on board and our Workshop & Recondition service covers inspection and reconditioning in the workshop. Tell us what you see through the contact page, and see Ultimate Turbocharging for the wider turbocharger service.
This article is general information and not a diagnosis of any particular unit. Always follow the manufacturer's instructions and the applicable class rules.