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Liquid Flow quantity and flow velocity measurement instruments

Liquid flow level,quantity,velocity parameters
Shipboard machinery must operate within certain desired parameters. Instrumentation enables the parameters—liquid flow level,quantity,velocity and so on—to be measured or displayed against a scale.



Flow measurement can be quantity measurement, where the amount of liquid which has passed in a particular time is given, or a flow velocity which, when multiplied by the pipe area, will give a rate of flow.

A rotating pair of intermeshing vanes may be used which are physically displaced by the volume of liquid passing through . The number of rotations will give a measure of the total quantity of liquid that has passed. The rotation transfer may be by mechanical means, such as gear wheels, or the use of a magnetic coupling. Another method is the use of a rotating element which is set in motion by the passing liquid .

A drive mechanism results in a reading on a scale of total quantity. The drive mechanism may be mechanical, using gear wheels or electrical where the rotating element contains magnets which generate a current in a pick-up coil outside the pipe.


Flow quantity measurementFig: Flow quantity measurement

Liquid flow velocity measurementFig: Ventury tube

Flow velocity measurement

The venturi tube

This consists of a conical convergent entry tube, a cylindrical centre tube and a conical divergent outlet. Pressure tappings led to a manometer will give a difference in head related to the fluid flow velocity. The operating principle is one of pressure conversion to velocity which occurs in the venturi tube and results in a lower pressure in the cylindrical centre tube.

orifice plateFig: Orifice plate

The orifice plate

This consists of a plate with an axial hole placed in the path of the liquid. The hole edge is square facing the incoming liquid and bevelled on the outlet side . Pressure tappings before and after the orifice plate will give a difference in head on a manometer which can be related to liquid flow velocity.



Ships instruments:

  1. Oxygen analyser working principle
    The measuring of oxygen content in an atmosphere is important, particularly when entering enclosed spaces. Also inert gas systems use exhaust gases which must be monitored to ensure that their oxygen content is below 5%. One type of instrument used to measure oxygen content utilises the fact that oxygen is attracted by a magnetic field, that is, it is paramagnetic....

  2. Temperature measurement instruments - use of Thermometers, Thermocouple, Radiation pyrometer & Thermistor

    Temperature measurement by instruments will give a value in degrees Celsius (°C). This scale of measurement is normally used for all readings and temperature values required except when dealing with theoretical calculations involving the gas laws, when absolute values are required.....

  3. Pressure measurement instruments - U-tube Manometer, Mercury Barometer & Aneroid Barometer
    Various liquids are used in this type of instrument, depending upon the temperature range, e.g. mercury -35 deg C to +350 deg C, alcohol -80 degC to 4-70°C. An increase in temperature causes the liquid to rise up the narrow glass stem and the reading is taken from a scale on the glass . High-temperature-measuring mercury liquid thermometers will have the space above the mercury filled with nitrogen under pressure.....

  4. Level measurement by Pneumatic gauge
    This is a device which uses a mercury manometer in conjunction with a hemispherical bell and piping to measure tank level. The arrangement is shown in Figure. A hemispherical bell is fitted near the bottom of the tank and connected by small bore piping to the mercury manometer. A selector cock enables one manometer to be connected to a number of tanks, usually a pair....

  5. Salinometer -How to determine water purity ?
    Water purity, in terms of the absence of salts, is essential where it is to be used as boiler feed. Pure water has a high resistance to the flow of electricity whereas salt water has a high electrical conductivity. A measure of conductivity, in Siemens, is a measure of purity.....

  6. Oil in water monitor
    Current regulations with respect to the discharge of oily water from ships set limits of concentration 15 parts per million. A monitor is required in order to measure these values and provide both continuous records and an alarm where the permitted level is exceeded.....

  7. Viscosity control of marine fuels
    Viscosity control of fuels is essential if correct atomisation and combustion is to take place. Increasing the temperature of a fuel will reduce its viscosity, and vice-versa. As a result of the varying properties of marine fuels, often within one tank, actual viscosity must be continuously measured and then corrected by temperature adjustment. ....

  8. Flow measurement
    Flow measurement can be quantity measurement, where the amount of liquid which has passed in a particular time is given, or a flow velocity which, when multiplied by the pipe area, will give a rate of flow.....

  9. Moving coil meter
    Electrical measurements of current or voltage are usually made by a moving coil meter. The meter construction is the same for each but its arrangement in the circuit is different.....

  10. Electrical and mechanical Tachometers
    A number of speed measuring devices are in use utilising either mechanical or electrical principles in their operation.....

  11. The measurement of torsion -Torsionmeters
    The measurement of torsion is usually made by electrical means. The twisting or torsion of a rotating shaft can be measured in a number of different ways to give a value of applied torque. Shaft power can then be calculated by multiplying the torque by the rotational speed of the shaft....

  12. Viscosity control of marine fuels
    Viscosity control of fuels is essential if correct atomisation and combustion is to take place. Increasing the temperature of a fuel will reduce its viscosity, and vice-versa. As a result of the varying properties of marine fuels, often within one tank, actual viscosity must be continuously measured and then corrected by temperature adjustment.....




Marine machineries - Useful tags

Marine diesel engines ||Steam generating plant ||Air conditioning system ||Compressed air ||Marine batteries ||Cargo refrigeration ||Centrifugal pump ||Various coolers ||Emergency power supply ||Exhaust gas heat exchangers ||Feed system ||Feed extraction pump || Flow measurement || Four stroke engines || Fuel injector || Fuel oil system || Fuel oil treatment ||Gearboxes || Governor || Marine incinerator || Lub oil filters || MAN B&W engine || Marine condensers || Oily water separator || Overspeed protection devices || Piston & piston rings || Crankshaft deflection || Marine pumps || Various refrigerants || Sewage treatment plant || Propellers || Power Plants || Starting air system || Steam turbines || Steering gear || Sulzer engine || Turbine gearing || Turbochargers || Two stroke engines || UMS operations || Drydocking & major repairs || Critical machinery || Deck machineries & cargo gears || Control and instrumentation ||Fire protection ||Engine room safety ||






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