Page 382 - The City and Guilds Textbook: Plumbing Book 1 for the Level 3 Apprenticeship (9189), Level 2 Technical Certificate (8202) and Level 2 Diploma (6035)

The City & Guilds Textbook: Plumbing Book 1

ACTIVITY

Working out the capacity of a cylinder calls for a relatively simple calculation
that involves the use of Pi (π). Take π as being 3.142.
The formula for calculating the capacity of a cylinder is:

π r 2 × h × 1000
where:
π = 3.142
r = radius
h = height
Example:
A cylinder has a diameter of 500 mm and a height of 1000 mm. What is its
capacity in litres?

Answer:
First, we will need to convert mm to m. Therefore, 500 mm becomes 0.5 m and
1000 mm becomes 1 m. The diameter is 0.5 m so the radius will be half of that.
Therefore, the calculation will read:
3.142 × (0.250 × 0.250) × 1 × 1000 = 196.375 litres
Now attempt the following calculations:
1 A cylinder measures 300 mm × 1050 mm. What is its capacity?
2 A cylinder measures 400 mm × 850 mm. What is its capacity?
3 A cylinder measures 500 mm × 1500 mm. What is its capacity?

Anodic corrosion protection of hot water storage cylinders
Hot water storage cylinders can suffer from electrolytic corrosion where there
are two or more dissimilar metals present, especially in areas where the water
is soft as this is aggressive to certain metals.

Placing two dissimilar metals in aggressive water produces a very small electric
current, which flows from the weaker (anodic) metal to the noble (cathodic)
metal where the anodic metal is gradually eaten away. This occurs commonly
when some types of brass fittings are used.

Hot water cylinders can be protected from electrolytic corrosion by the use of a
magnesium rod, which is either fastened to the bottom of the storage cylinder
during manufacture or by simply dropping the magnesium rod in the draw-off
connection during installation. This magnesium rod is known as the sacrificial
anode. It works by distracting the corrosion away from the weaker anodic metal
in the installation to be eaten away itself. If necessary, it can be replaced once
the anode has been completely destroyed.

Pipe sizes for open vented hot water storage systems
Pipe sizes are critical if the correct flow rate is to be achieved at the outlets.
For open vented hot water systems fed from a cistern in the roof space, the
size of the pipework would generally depend on the size of the system. A
minimum 22 mm cold feed pipe to the cylinder should be installed, with a
full-way gate valve to provide isolation of the hot water system.

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