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Usually， surge is linked with excessive vibration and an audible sound;yet，there have been cases in which surge problems， which are not audible， have caused failures.
Failure .iagnostics
Problem evaluation in turbomachinery is complex， but with the aid ofperformance and mechanical signals， solutions can be found to diagnose various types of failures. This is done by using several inputs and a matrix. A sample of some of the problems are given in the next few sections.
Compressor .nalysis
Compressor analysis is done by monitoring the inlet and exit pressuresand temperatures， the ambient pressure， vibration at each bearing and the pressure and temperature of the lubrication system. Table 19-5 shows the effect various parameters have on some of the major problems encountered in a compressor. Monitoring these parameters allows the detection of:
1.  Clogged air ilter. A clogged air filter may be detected by noting an increase in the pressure drop through the filter.

2.  Compressor surging. Surge may be detected by noting a rapid increasein shaftvibration， along with a discharge pressure instability. If more than onestage is present， the probes located within the bleed air chambers are useful in locating the problem stage by checking for pressure fluctuations.

3.  Compressor ouling. This is indicated by a decrease in pressure ratio and flow accompanied by an increase of exit temperature with time. The change in the temperature and pressure ratio tend to show a decrease in efficiency. If a change in vibration hasoccurred， the fouling iscritical， since it indicates excessive build up of deposits on the rotor.

4.  Bearing ailure. Symptoms of bearing trouble include a loss of lub-rication pressure， an increase in the temperature difference across thebearing， and an increase in vibration. If oil whirl or other bearinginstabilities are present， there will be a vibration at subsynchronous frequency.

Table 19-5
Compressor .iagnostics

η.  ....1  ....1  .ass  .ibration  !.  Bearing  Bleed 
Flow  Bearing  .ressure  Chamber 
.ressure 

Clogged    filter Surge   .ariable   Highly    Highly fluctuating fluctuating Fouling        Damaged        Highly blade fluctuating Bearing      failure
Combustor .nalysis
In the combustor， the only two parameters that can be measured are fuel pressure and evenness of combustion noise. Turbine inlet temperatures are not usually measured due to very high temperatures and limited probe life. Table 19-6 shows the effect of various parameters on important functions of the combustor.
Table 19-6
Combustor .iagnostics

Fuel  Unevenness of  E.haust  E.haust 
.ressure  Combustion  Temperature  Temperature 
.Sound.  Spread 
Clogging  . . . . 
Combustor fouling  ..or  . . . 
Crossover tube failure  ..or  - .+  -
Detached or cracked liner  ..or  . . -

Figure 19-.0. E.ui.alent engine time in t.e combustor section.
The measurement of the two parameters allows the detection of:
1.  .lugged no..le. This is indicated by an increase in fuel pressure in conjunction with increased combustion unevenness. This is a common problem when residual fuels are used.

2.  Cracked or detached liner. This is indicated by an increase in an acoustic meter reading and a large spread in exhaust temperature.

3.  Combustor inspection or o.erhaul. This is based on equivalent enginehours， which are based on the number of starts，fuel， and temperature. Figure 19-20 shows the effect of these parameters on the life of the unit.

　
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