Sunday, February 26, 2012

Controls and instrumentation - Oil temperature and pressure

want to read about : Controls and instrumentation - Turbine gas temperature

Oil temperature and pressure 

35. It is essential for correct and safe operation of the engine that accurate indication is obtained of both  the  temperature  and  pressure  of  the  oil.  Temperature  and  pressure  transmitters  and indicators are illustrated in fig 12-9.
Fig. 12-9 Oil temperature and pressure transmitters and indicators.
36. Oil temperature is sensed by a temperature- sensitive element fitted in the oil system. A change in temperature causes a change in the resistance value and, consequently, a corresponding change in the current flow at the indicator. The indicator pointer is deflected  by  an  amount  equivalent  to  the temperature change and this is recorded on the gauge in degrees centigrade.
37. Oil pressure is electrically transmitted to an indicator on the instrument panel. Some installations use  a  flag-type  indicator,  which  indicates  if  the pressure is high, normal or low; others use a dial- type gauge calibrated in pounds per square inch (p.s.i.).

38. Electrical operation of each type is similar; oil pressure, acting on the transmitter, causes a change in the electric current supplied to the indicator. The amount of change is proportional to the pressure applied at the transmitter.
39. The transmitter may be of either the direct or the differential pressure type.  The latter senses the pressure difference between engine feed and return oil pressures, the return oil being pressurized by cooling and sealing air (Part 9) from the bearings.
40. In addition to a pressure gauge operated by a transmitter, an oil low pressure warning switch may be provided to indicate that a minimum pressure is available for continued safe running of the engine. The switch is connected to a warning lamp in the flight compartment and the lamp illuminates if the pressure falls below an acceptable minimum.

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