manometer measuring tanks

7/14/2019 manometer measuring tanks

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Marine Engineering Knowledge (General)

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P L E A S E U S E T H I S B O O K F O R R E F E R E N C E O N L Y . P L E A S E D O N O T X E R O X . H E L P

U S B Y B U Y I N G O R I G I O N A L C O P I E S F R O M U S . W W W . D I E S E L S H I P . C O M

Q2. (a) Sketch and describe TWO methods that employ manometric means for measuring tank contents.A. State what corrections are made to the readings obtained by the methods described in (a) in order to gauge the masscontents,B. Explain how bunkering requirements may be estimated when no records of main engine fuel consumption areavailable on board.

2008/sr4 2007/sr10 2007/sr1 2006/sr4 2010/sr1 2012/SR42013/sr3 2013/sr6

MANOMETRIC MEANS FOR MEASURING TANK CONTENTS:1. BUBBLER GAUGE

* In this application, a dip tube is usually inserted from the tank top, and is particularly useful where bottom access is

not possible. The dip tube is fed with an air pressure at some value above the maximum static pressure created by the

head of liquid in the tank, such that there is a small air flow from the bottom of the dip tube about 0.225 m3 / hour.

* The back pressure in the dip tube caused by the static head of liquid in the tank is then measured and an indicator

may be locally or remotely mounted, calibrated in level or quantity units. When the indicator is remotely mounted the

connection to the airline must be as close to the dip tube as possible to avoid errors being introduced by the pressure

drop along the line of the flow meter unit to the tube.

2. Differential pressure gauge.For open tanks:


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For a closed tank

* As shown in picture, in a close tank level measurement installation, if a gas phase exists on top of the liquid, the gas

pressure must be compensated for. This is because a change in the gas pressure will cause a change in the level

transmitter, LT, output. Furthermore, the pressure exerted by the gas may be so high that the pressure due to the column

of liquid becomes insignificant.

* A pressurized close tank application requires a reference connection. A reference connection is a connection from the

transmitter (LT) low side to the top of the tank. Its purpose is to compensate and balance out the pressure above the

liquid so that a true level measurement can be made. If there were no reference or compensating connection, the

transmitter would indicate the level plus the tank pressure:

From the diagram above, P (high) = P (gas) + H X S.G

and P (low) = P (gas)

Differential Pressure, P = P (high) P (low)

P = P(gas)+H X S.G P(Gas)

P = P(gas)+H X S.G P(Gas)

P = H X S.G

Sensor transducer and controllers which are electronic components can be individually checked against known inputvalues and output mill volt readings measured and compared with the makers test figures. Any deviation from maker

test figures indicate faulty equipment and needs to be changed. Normally printed circuit boards which are found


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defective have to be replaced from spares, as these boards are difficult to repair on board without the use of precision

testing equipment. In the event of failure of main engine remote control system the control would be changed over to

the local manual control position automatically and the duty engineers have to following instructions, till the system is

restored to the normal conditions.

Corrections: -Corrections are made on

1. Temperature correction.

2. Trim and heel correction.

Temperature correction is necessary because the liquid in the tank might be in a different temperature from the

temperature at which the gauges were calibrated, so the reading may be wrong if not corrected.

Trim and heel correction to be taken due to the head change corresponds to a major difference due to the area of the

tank is huge.

Let,

Here,

Specific gravity of the liquid at measured temperature Specific gravity of the liquid of the calibrated temperature

t the difference in temperature in oc between the present temperature and calibrated temperature.

Thermal coefficient of expansion of the liquid.

So,

Pressure = H X X gH = height of liquid in the tank.

B. Explain how bunkering requirements may be estimated when no records of main engine fuel consumption areavailable on board.Fuel consumption / unit time power developed

Fuel consumption / unit sp

And since sp 2/3 x v3

Fuel consumption / unit time 2/3 x v3

Tonnes

Values of fuel co-efficient vary between about 40,000 and 120 000, the higher values indicating more efficient ships


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If D is the distance travelled at v knots, then:

Number of days

But daily consumption v3

Total voyage consumption v3 x v2 D

i.e =

2Hence, for any given distance travelled the voyage consumption varies as the speed squired.

By this method if one previous voyage total consumption and total distance with vessel speed is known to us. Then the

present voyage total distance is known to us. We know what will be the vessel speed to cross this distance, so from the

above formula we can easily calculate the consumption for the intended voyage.

Voyage consumption 2 = Voy. Cons1

manometer measuring tanks

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