130
to the brake shoe. The diameter of the impression was measured
with a micrometer microscope and the corresponding pressure de-
Fig. 73.
BRAKE SHOE PRESSURE MEASURING DEVICE.
The application to the No. 1 clasp brake.
CLASP NO. /
CL ASP NO. 2
Fig. 74.
BRAKE SHOE PRESSURE MEASURING DEVICE.
As applied to the No. 2 clasp brake.
SO
termined from a calibration curve of similar impressions made under
direct known pressure on a testing machine.
• 291. The ratio of the pressure at the brake shoe as found by this
method, to the brake shoe pressure which should result from the cylinder
pressure and the total lever ratio known to exist, represents the mechan-
ical efficiency of the rigging in per cent.