Air Pumps.

19. The tophead main valve piston rings should be a good fit (without being too tight) in the cylinders or bushes. These rings should fit the piston head grooves closely and without shake. The piston ring ends should fit closely together.

20. When air pumps are being overhauled, the steam and air cylinders should be callipered, to see if these cylinders are parallel, before the piston rings are fitted.

21. The steam and air cylinders should be rebored when the ends are 1–16th in. larger than the centre of the bore.

22. Air cylinder piston heads should be replaced when the diameter is 1–16th in. less than the bore of the cylinder.

23. The fit of the air piston head on the rod should be a light driving fit when the end of the rod is parallel, but when the piston rod end is tapered there should be 1–32 in. draw.

24. Piston packing rings for air or steam cylinders should be condemned when the openings are 3–32 in. apart when placed in the end of the cylinder.

25. Piston rods should be trued up when cut or worn 1–32 in.

26. All screws and threads should be coated with graphite lubricant before being fitted together.

27. Steel air valves are preferable for all air pumps.

28. Worn nuts should never be placed on the air piston rod end.

29. The air end of the piston rod should be annealed each time the air pump is overhauled.

30. The lift of the air valves should be minimum 3–32 in., maximum 5–32 in.

31. It is important that the steam and air cylinders of the air pump be properly and regularly lubricated with suitable oil or grease.

32. Oil the steam cylinders with good cylinder oil and the air cylinder with paragon grease.

33. Tallow or animal or vegetable oils must not be used to lubricate the air cylinder.