Abstract: An impeller on a stirrer shaft is rotated at constant angular velocity by a motor within a chamber. Vibrations induced in the shaft by virtue of the stirring action of the impeller are sensed by a transducer whose output is conditioned by equipment from these signals. The invention can be applied to processes in a reaction vessel and liquid in a pump chamber. Since the excitation is a constant angular velocity and the induced effect is vibration, there is no interference between excitation and induced effect although the transducer is mounted on the stirrer shaft.

Abstract: A high-pressure piston pump in which a low-viscosity working liquid supplied at a first pressure is delivered at a second, ultra-high pressure of, typically, up to 4,000 bars, for use in jet cutting and cleaning operations comprises a cylinder enclosing a first variable volume chamber for a viscous, operating liquid between a main piston and a subsidiary piston, and a second variable volume chamber for the working liquid, between the subsidiary piston and the head end of the cylinder. Operating liquid which leaks from the first chamber during working strokes of the pump and which thus reduces the volume of liquid in the first chamber, is replaced through a non-return valve in the main piston during non-working strokes as a result of the reduction in pressure in the first chamber. The subsidiary piston is provided with a coupling engageable with the main piston for limiting movement of the main piston away from the subsidiary piston during non-working strokes of the pump.