Within the re-entrant
piston and cylinder design, the test
fluid is applied to a chamber on the
outside of the cylinder as well as to
the inside of the cylinder. The area of
the outside of the cylinder is larger
than the inside giving a reduced
clearance between the piston and the
cylinder at higher pressures. This
design reduces the rate of fluid
leakage, thus increasing the time
available for calibration of instruments
prior to pumping to restore fluid loss.
