CASE 5.--Where the air is used without heating, and cut off at one-third
of the stroke, as in ordinary slide-valve engines

CASE 6.--Where the air is used without re-heating and without expansion.

_____________________________________________________________________
| Qty. Air | Cost/Hr. | Cost/Hr. | Cost/Yr. | Cost/Yr. |
| | | w/rebate | | w/rebate |
| Cub. Ft. | d. | d. | £ s. d. | £ s. d.|
---------------------------------------------------------------------
CASE 1 | 125.4 | 0.627 | 0.596 | 7 1 1 | 6 14 0½|
CASE 2 | 140.4 | 0.702 | 0.667 | 7 17 11 | 7 10 0 |
CASE 3 | 178.2 | 0.891 | 0.847 | 10 0 5½ | 9 10 5½|
CASE 4 | 170.2 | 0.851 | 0.809 | 9 11 5½ | 9 1 10½|
CASE 5 | 258.0 | 1.290 | 1.226 | 14 10 3 | 13 15 9 |
CASE 6 | 331.8 | 1.659 | 1.576 | 18 13 3 | 17 14 7 |
_____________________________________________________________________

The great thing to guard against is leakage. If the pipes were simply
buried in the ground, it would be almost impossible to trace leakage, or
even to know of its existence. The income of the company might be
wasting away, and the loss never suspected until the quarterly returns
from the meters were obtained from the inspectors. Only then would it be
discovered that there must be a great leak (or it might be several
leaks) somewhere. But how would it be possible to trace them among 20 or
30 miles of buried pipes? We cannot break up the public streets. The
very existence of the concern depends upon (1) the _daily_ checking of
the meter returns, and comparison with the output from the air
compressors, so as to ascertain the amount of leakage; (2) facility for
tracing the locality of a leak; and (3) easy access to the mains with