42. If the hole in the vent screw is closed up, the air pump will be slow in starting after being stopped owing to the compressed air above the governor piston not being able to pass through the vent hole to the atmosphere.

43. Dirt on the seat of the pin valve, or a leaky pin valve, will stop the pump or make it work slowly.

44. Worn steam rod and valve, will cause a blow of steam from the governor drain and relief ports.

45. Air pumps can be defective through the following causes:—Want of lubrication, defects in slide valve, piston rings, reversing plate, reversing rod, reversing valve, worn cylinders or bushes, air valves, valve cases, gland packing, dirty pump strainers, and running at excessive speed.

46. Driver's brake valve defects may be due to leaky rotary valve, worn equalising piston rings or cylinder, worn handle stops, defective feed valve or spring, water or leaks in the equalising reservoir or its connections. When brake valves are overhauled the equalising piston, its ring and cylinder, should all be examined. The piston ring should be tested as per the triple valve piston ring test.

47. Triple valve defects arise from worn or defective piston rings, bushes, feed grooves, graduating valve, leather gaskets, check valves

48. Brake cylinder defects may be caused by want of lubrication, defective piston leather, leakage groove stopped up, broken or defective leather packing expander, studs slack in the piston head, dirty or corroded brake cylinder, broken release spring, or leaky joints.

40. Release valve defects occur through defective or loose leather packing, defective valve seat, exhaust ports closed up, or handle sticking and keeping valve open.

50. Retaining valve defects: defective or broken weighted valve, defective valve seat, or leaky pipe connections.

51. Equalising reservoir defects: reservoir partly filled with water, leaky pipe connections. (Equalising reservoirs should be so placed that they can be easily drained by the engine-drivers).

52. Brake cylinder piston travel: short travel gives high brake power. Long travel gives low brake power.

Table of Piston Travel and Resultant Cylinder Pressure.

From 70 pounds auxiliary reservoir and train pipe pressure.