Abstract: A system for use in connection with a flowmeter (volume flow rate), liquid level detector for a storage tank, a pressure indicator or otherwise. A pair of bellows assemblies connects a pressure source to a pressure sensitive instrument via conduit means including a detachable coupling. One bellows can be permanently (welded) attached to the pressure source. The instrument may be removed for service by uncoupling. The conduit means can carry two liquids separated by a bellows. One liquid may be NaK (a sodium and potassium mixture) which is used for radioactive applications and to detect the liquid level of a 1000.degree.F. liquid sodium storage tank or the pressure or liquid level of a corrosive liquid. The other liquid can be an oil that transmits the NaK pressures to the pressure sensitive instrument. The detachable coupling is a double-seal type (both halves automatically close), and is placed in the oil-filled conduit. The oil-filled conduit is not subjected to high temperatures.