Flow Measurement Techniques for Hydraulic Dredges

Hydraulic dredges are being equipped with metering systems that furnish direct readout of spoil velocity, density, and solids flow rate. The latter is time-integrated to produce a continuous cumulative number display that is proportional to total solids transported in the pipeline. Two types of systems have been developed; one uses all-pneumatic instrumentation, the other uses all electric instrumentation. First cost of the electric system is approximately four times that of the pneumatic. The electric is more complex and generally beyond the maintenance capabilities of dredge personnel. However, it is somewhat more trouble-free and a little faster in response. The pneumatic systems use instruments that sense differential pressures at purge taps in the pipeline and deliver pneumatic signals in the ISA standard 3 psi to 15 psi signal band. The electric system uses especially built large magnetic flow meters to produce a velocity signal and a radioactive density gage (gamma ray source). Pneumatic and electric computation is used in the respective systems.