grout line, one at the pump and the other at the hole for control. When there
is the possibility of doing serious damage by the application of too much
pressure, all gages should be installed in duplicate. Structures have been
damaged by the unintentional application of excessive pressure occasioned by
gage failure or sticking. Gages, the glass faces of which have been broken,
should be condemned. Dust and grit tend to reduce the accuracy of the gage.
This causes the gage to register falsely and results in pressures higher than
those indicated being applied, with attendant higher grout injection. The gage
used should have a pressure range comparable to that required. Thus, a
200-psi-capacity gage is not appropriate for grouting where a maximum
pressure of 50 psi is contemplated.
(2) The moving parts of the gage must, for obvious r e a s o n s , be pro-
tected from direct contact with the grout. The simplest protective device for
pressures greater than 200 psi is a short oil- or grease -filled siphon (pig-
tail) located between the gage and the grout. This consists of a l/4-in. pipe
with a 3-in. loop in its center. The pipe is filled with a light grade of water -
p r o o f grease. An alemite fitting, located between the gage and the pigtail,
enables the operator to force open the passage should it become obstructed.
However, grease makes the gage sluggish and its readings are not always
consistent due to the effect of temperature changes on the fluidity of the
g r e a s e . The most satisfactory device consists of a piece of 1-1/2- or 2-in. -
diameter pipe 18 in. long that is stubbed off vertically above the grout line.
The gage is fitted to the top of this stub by means of suitable bushings. All