MEASURES, WEIGHTS

MEASURES, WEIGHTS, &c. USED IN THIS WORK.

Temperature is measured by degrees of Fahrenheit's scale, of which the freezing point is

32, and the boiling point 212.

Heat is commonly measured by the number of degrees it would increase the temperature of

a given quantity of water at 60, with the barometer at 30 inches. 1

Mechanical power is measured by the elementary horse power, as settled by Watt. A

horse power is = 33,000 ffis. raised one foot high per minute, or = 550 Ibs. raised one

foot high per second ; and a day's work of a horse is this power acting 8 hours.

This horse power is, in French measures, 4661 kilogrammes raised one metre high per

minute.

The pound is the avoirdupois pound, = 7000 troy grains, = '4535 French kilogrammes.

The foot is = -3048 French metre.

( 30 inches 1 , An atmosphere is =

| .^62 metre j

of mercury.

= 14*70 Tbs. per square inch.

= 11 '55 circular

1 It is more properly measured by the volume of water at 60, which it would raise exactly one degree ; this measurement

being strictly proportional to the absolute quantity of heat. ED.

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BASIC KNOWLEDGE OF ELECTRICITY

BASIC KNOWLEDGE OF ELECTRICITY

Electric Circuit-a network of paths designed for electric current to carry out a

specified function.

Circuit Breaker - one form of switch providing ON/OFF function and

automatic tripping of the electric circuit in the event of short

circuit or circuit overload. The point at which the breaker

trips depends on the rating of the circuit. The breaker can be

reset to operate again after the fault has been cleared.

Fuse - a conductor, usually in the form of a wire or a cartridge, of low melting

point material placed in the electrical supply circuit and forms part of

the circuit. It serves to protect the electric circuit from short circuiting

or overloading. It melts to interrupt the electricity supply because the

excess current produces a large amount of heat. Unlike the circuit

b r e a k e r, it must be replaced with a new unit after blowing.

Earth Line - a conductor or wire which electrically connects the boiler metal

casing with the earth terminal provided by the electricity supply

c o m p a n y. This line plays a very vital role in the prevention of

electric shock.

Electric Shock - this is a phenomenon whereby the human body has become a

path for electric current. The human body may suffer burns

and heart difficulties which can result in death.

When an electric wire of high potential becomes loose or exposed and is in

contact with the metal casing of the boiler, the casing will also be at a high

potential relative to the earth. If the earth line is also defective, the casing will

be maintained at a high potential. There may not be any indication of the high

potential but when a person is in contact with the casing and he is also in

contact with the earth, an electric path for current is established through the

human body. Potential differences above 50V, A.C. or D.C., are able to drive

electric current through the body. This is what is termed an electric shock.

Alternating current has a more serious effect in that it can cause the victim to

become paralysed while still holding firmly onto the faulty electric part. The

normal mains supply in Hong Kong is nominally 220V A.C. which is well

above the threshold voltage of 50V. However, it should be noted that,

depending on the physical conditions of a person, potential difference less than

this threshold voltage has been known to cause serious injuries.

I M P O RTANT NOTE:- Never try to repair any faulty electric circuit. The

repair should be carried out by a registered.

electrical worker only.

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BLOWING OF WATER LEVEL GAUGE of a Boiler,Procedure of blowing through a gauge glass.

A Typical Water Level Gauge

It is a very common design to have all the FIVE cock handles pointing

downwards while the water gauge is in use.

Procedure of blowing:-

When the boiler is in operation, the steam cocks A, D and water cocks B, E are

open and drain cock C is shut.

(a) First shut both steam and water cocks A, D, B and E. Open drain

cock C to prove that all the gauge cocks are in order. Then, with the

drain cock C still open, cocks B and E should be opened. If water

blows out freely from cock C, cocks B and E are clear.

(b) Shut off cocks B and E and open cocks A and D with the drain cock

C still open. If steam blows out freely from cock C, cocks A and D

are clear.

(c) To cross test, close cocks D and B, leaving E, A and C open. If water

blows out from cock C, then E, A and the water-column are in order.

(d) Close cocks E and A, leaving D, B and C open. If steam blows out

from cock C, then D, B and the water-column are in order.

When any of the cocks are found to be clogged, shutdown the boiler and

overhaul the water level gauge.

Possible causes of gauge glass indicating incorrect level

(a) If cocks A and D or steam passage is shut or choked, boiler pressure

will press the water level in the glass higher than the real water level

of the boiler. The water level indication in glass will, therefore, be

i n c o r r e c t .

(b) If cocks B and E or water passage is shut or choked, steam will

condense on upper column of glass and accumulate. The apparent

water level shown can be higher than the actual water level, causing

false reading.

Water gauge glass should be tested daily at l e a s t at every change of attendant.

The safety of boiler operation relies greatly on proper functioning of the water

gauge glass.

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Basic Water Tube Boiler

Basic Water Tube Boiler

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Feed Water System of a Boiler

Feed Water System of a Boiler
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Fire Tube Boiler details.

Fire Tube Boiler details.
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Provision of Fire Extinguishers in case of uptake fires in a boiler

Provision of Fire Extinguishers

The owner must provide one set each of the following types of fire

extinguishers near the entrance to the boiler room:-

(a) at least one 9 litres (2 gallons) foam extinguisher for oil fire;

a n d

(b) at least one dry powder extinguisher or carbon dioxide

extinguisher for electrical fire.

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uptake fires in a boiler on board or ships

Soot and unburnt carbon can deposit on the walls of the boiler uptake

(chimney). They form, in effect, another fuel and can catch fire in

the uptake. Although uptake fires do not often occur, they can be

very difficult to extinguish and the hazard builds up quietly and

usually undetected. The fire is caused by smouldering of the deposits

accumulated in the uptake. It usually occurs during boiler shutdown

or under light load condition. There is evidence that under normal

loads the flue gas "cools" the soot and the carbon deposits so that a

smouldering fire does not occur. In the absence of flue gas or if the

flue gas flow is insufficient to cool the deposits, they can catch fire.

When an uptake fire occurs, it results in very high exhaust

temperatures and excessive thick black smoke, mixed with sparks,

coming out of the uptake. The boiler must be shutdown immediately

and the blower switched off or the damper closed to stop any air

supply to the uptake. The fire service must be called. If the uptake is

common for several boilers, all the boilers must be shut down. The

key point is to stop the boiler air supply. No attempt should be made

to extinguish the fire by water unless the water supply is plentiful. A

steam fire may result if the water supply is not plentiful. The fire

should be allowed to die out. The fire must be contained by

restricting and removing any combustibles in the near vicinity.

To prevent an uptake fire, the operator must clean the uptake

periodically to eliminate accumulation of soot and unburnt carbon.

He should also exercise care in the daily operation of the boiler and

maintain the correct air/fuel ratio to ensure complete combustion of

fuel and minimize production of soot or unburnt carbon.

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