Abstract: McLeod gauge has controllable fluid communication between the top of the closed end capillary and the top of the comparison capillary to enable easy degassing of the closed end capillary, thereby enabling optional use of low density non-volatile pressure measuring fluids in place of mercury.

Abstract: A by-pass flowmeter of coaxial design comprises a transparent outer tube and a rotameter coaxially disposed within the outer tube and laterally spaced therefrom to define an annular by-pass chamber. An inlet is at least partially disposed within one end of the outer tube in fluid communication with both the rotameter inlet and an adjacent portion of the by-pass chamber while an outlet is at least partially disposed within the other end of the outer tube in fluid communication with both the rotameter outlet and an adjacent end portion of the by-pass chamber. As the by-pass flowmeter is of coaxial design, greater accuracy is obtainable than with by-pass flowmeters of non-coaxial design.