joints should be made tight with litharge and glycerin or lead since the
device is, in effect, an air dome and any small air leak will render it inef-
f e c t i v e . The gage is very sensitive with this arrangement and the violent
oscillations of the needle make exact readings difficult; but this objection-
able feature can be largely obviated and the gage given additional protection
by installing a gage saver, as shown in figure 17, between it and the air
dome.
f . Valves for Grout Line. Plug valves should be used to control the
flow of grout. Pressure relief valves are sometimes installed in the grout
line as an added precaution in controlling grout pressures, but should not be
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