Q) Write short notes on: Use of indicator card on board.
Ans:- Use of indicator card on board:
- Power Card is the measurement of the variation of pressures in a cycle.
- Irregularities in the shape of the diagram will show operational faults. Maximum or peak pressure may be measured to scale between the atmospheric line and the highest point on the diagram.
- Compression diagram is taken in a similar manner to the power card but with the fuel shut off from the cylinder.
- The height of this curve shows maximum compression pressure. If compression and expansion lines coincide, it shows that the indicator is correctly synchronized with the engine.
- Reduction in height of this diagram show slow compression, which may be due to worn cylinder liner, faulty piston rings, insufficient scavenge air or leaky exhaust valve, any of the which will cause poor combustion.
- Draw card or out of phase diagram is taken in a similar manner to the power card, with fuel pump engaged but with the indicator drum 90″C out of phase piston stroke. This illustrates more clearly the pressure changes during fuel combustion. Fuel timing or injector faults may be detected from its shape.
- Light or Weak spring diagram is again similar to the power card and in phase with the engine, but taken with a light compression spring fitted to the indicator showing pressure changes during exhaust and scavenge to an enlarged scale.
- It can be used to detect faults and scavenge to an enlarged scale. It can be used to detect operations.