Define siphonage, ductile, creep, tensile strength, malleable and state two systems of domestic hot water supply.

21. (a) Define the term "siphonage" as related to plumbing.
Siphonage in plumbing refers to the loss of the water seal in a trap due to negative pressure (suction) in the drainage system. This negative pressure can pull the water out of the trap, allowing sewer gases to enter the building.

21. (b) State two instances in plumbing where siphonage may be used as an advantage.

• The siphonic action is used to flush toilets, effectively emptying the bowl.
• Siphons can be used to drain liquids from a higher level to a lower level without mechanical pumping, for example, draining a tank or a pond.

22. Explain the meaning of the following physical properties.

• (i) Ductile: The ability of a material to be drawn or stretched into a thin wire without fracturing.
• (ii) Creep: The tendency of a solid material to deform permanently under the influence of mechanical stresses over a long period, even at stresses below its yield strength.
• (iii) Tensile strength: The maximum stress that a material can withstand while being stretched or pulled before breaking.
• (iv) Malleable: The ability of a material to be hammered or pressed permanently into thin sheets without breaking or cracking.

23. State any two systems of domestic hot water supply commonly used.

• Direct hot water system (or Vented system)
• Indirect hot water system (or Unvented system)