and 12 until the expansible members are fully pressurized a check valve controlled fill port 94 provides an auxiliary access to the expansible members or gas springs to enable them to be filled manually from an outside pressure source with reference to fig4 other pressure amplifiers may of course be utilized for example the low pressure chamber 80 may be defined in a first rolling diaphragm 100 and the high pressure chamber may be defined in a second rolling diaphragm 102 a push rod 104 interconnects the two diaphragms to transfer force from one to the other the low pressure diaphragm is larger in diameter than the high pressure diaphragm by an amount selected in accordance with the desired pressure ratio the rolling diaphragm embodiment is advantageous in that a very low friction and leakage are encountered a vent 106 assures that a negligible and common pressure is provided between the two diaphragms by venting any build up of pressure which might tend to negate pressure intensification or to invert the diaphragms optionally direct fluid communication tubing and valves may be provided for connecting the pressure amplifier f directly with the compressor a or another source of pressure if high pressure is always available e g directly from the compressor a then the source of higher pressure may be connected directly to the.