TURBOCHARGER MAINTENANCE

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Contamination and Cleaning:

To ensure efficient functioning of the turbocharger it is essential not only to protect the bearings but also the compressor and turbine from contamination. At the intake to the compressor a filter/silencer is fitted. Between the compressor outlet and the engine an air-cooler is situated. Both these units are subject to fouling and should be cleaned regularly. In both cases a constant check should be kept of the pressure drop across these units, as this will give an indication of the degree of fouling.

Even with good filtration of air, deposits will build up after a period in the air passages through the compressor and on the tubes of the air cooler which will eventually cause a decrease of the boost pressure and consequent rise in exhaust gas temperatures. When intercoolers have been neglected and have become heavily contaminated the reduced airflow could cause the compressor to surge. The airflow through the compressor reverses in at least some of the passages. This can be heard, depending on the degree of contamination and the type of diffuser, as a type of buzzing or as a series of explosions. Surging of the compressor can also happen with clean intercoolers during quick accelerations or shut down of the engine. This temporary surging of the compressor is harmless whereas continuous surging can lead to breakdown.

Turbocharger Maintenance:

To ensure satisfactory operation of turbo-charges during service, general maintenance should be carried out regularly. The maintenance schedule depends on type of turbocharger, site conditions, operating conditions and company policies depending upon experience.

However a typical schedule is as follows:

Daily:

1. Check oil level.
2. Check performance.
3. Check cooling system

After First 100 Hours:

1.      Check holding down and easing bolts.

2.      Drain and clean oil sumps.

3.      Replenish with clean oil

Every 250 Hours:

1. Clean air filter element

Every 500 Hours:

1. Drain and clean oil sumps and refill with clean oil.

Every 6000- 8000 Hours:

1. Dismantle and overhaul.
2. Renew Bearings.

Cleaning Air filter:

The choice of cleaning agent will depend on the type contaminants and the type of filter element.

Some cleaning agents are:

a)      Colosyl, tri-soduim phosphate or house hold detergent and water.

b)      Soda solvents (Max. concentration 1%).

c)      Paraffin, kerosene.

d)     Mixture of 6.5% trichlorethylene, 9.5% teepol shell, 4% cyclohexanon and 80% fresh water.

Cooling water spaces in the Turbine Casing cleaning agents:

A 5% hydrocodoric acid solution can be used. To protect the case iron and immunising agent should be added to the mixture e.g. 0.5% by volume bone glue.

Before cleaning, the anti-corrosion plugs should be removed.

As explosive gases can be generated during cleaning, precautions to avoid explosion must be taken.

Bearings and bearing housing cleaning:

These should be cleaned with paraffin (kerosene) to which 20% clean mineral oil has been added. Petroleum spirit must not be used because the parts will rust.

Sealing ducts and bushes cleaning:

Sealing duct should be cleaned and blown through with air. Sealing bushes must be firm in the casing and their grooves undamaged.

Blower and Turbine cleaning:

During overhaul unleaded motor fuel or paraffin can be used for cleaning. However, usually blower can be most easily cleaned with any non-Toxic, non-inflammable, grease dissolving fluid, while the turbine including gratings, turbine wheels, and nozzle assemblies can be cleaned by submerging in hot water bath and then scrapping off the deposits softly and carefully with a wooden scraper or soft.   Turbine side can be cleaned during operation with the help of a nozzle, which injects atomised water.

The air pressure used is approximately 6 bar, and water pressure approximately 3 bar. Compressor side can also be cleaned by water injected from a small container.

 

Procedures are as follows:

 

Turbine Side:

1. Reduce the load of engine so as to reduce turbine r.p.m, approximately to 1/3 of the normal load.
2. Open drain cock at turbine bottom. Make sure that it is clear, and the pipe to bilges from the collecting funnel is clean.
3. Insert the cleaning nozzle in the pipe bend just before Turbocharger.
4. Open air and water supply.
5. Keep washing for 10-15 minutes until water observed form the drain is carbon and dirt free.
6. Close the air and water supplies and take out the cleaning nozzle.
7. Increase the power of engine slowly to normal over a period of 10-15 minutes.

Compressor side:

1. Fill up water in the container (1 to 2 litre depending on blower size) fixed on blower easing for this purpose. Don't use water connection from supply.
2. Inject water for 4 to 10 seconds at full load with the engine warm. If unsuccessful repeat it after at least 10 minutes period.

Turbine side washing should be done once a week or when necessary, while compressor side washing can be done daily or when necessary. However, large amounts of water for heavy cleaning should not be used for compressor side due to risk of air cooler fouling and water ingress in air.

The following data should be entered into the log for proper Turbocharger Operation:

1. Output of the Diesel engine.
2. Speed of the Diesel engine.
3. Air inlet temperature.
4. Pressure loss in the air filter.
5. Pressure of the charge air.
6. Pressure loss in charge air cooler.
7. Air temperature after the blower, also after the air cooler if fitted.
8. Inlet temperature of the cooling water to the air cooler.
9. Outlet temperature of the cooling water from the turbine easing.
10. Exhaust gas temperature after the cylinder.
11. Exhaust gas temperature before the turbine.
12. Turbocharger speed.

The close monitoring of these parameters gives good indication of turbocharger operation and the common operational problems.