Re-entrent piston/cylinder

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.