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FEATURES
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material,” says Shaun Coombes, co-owner of
Alltrap Engineering.
He adds that most building codes require
separators to be vented back through the inlet
plumbing and to a roof vent. “In almost all
cases, odour problems are caused by improper
venting of the building’s plumbing system.”
Squeaky clean
One of the advantages of modern traps
constructed from plastic materials is the
ease with which they can be dismantled
for cleaning.
Traps should be self-cleaning, that is to say,
they should be designed so that their walls are
scoured by the discharging water. The interior
surface of the trap should be smooth so that
water flow is not obstructed, thereby enabling
self-cleansing to take place.
An access door should be provided to assist
with cleaning the trap, which ideally should be
made from a non-absorbent material.
Good traps should provide enough water seal
(around 50mm) with a large surface area. The
depth of a trap seal depends on the intended
use of the pipe, and varies from 25mm to
75mm deep.
If the trap seal is lost or damaged, odours
from sanitary appliances will enter the home
or building. Therefore, the water seal in the
trap must be inspected and maintained in all
circumstances.
For multiple storey applications, a reseal trap
is used. Due to multiple floor installations
having their plumbing in-line with one
downpipe, the reseal ‘bubble’ breaks the
suction and ensures water is left in the seal.
Some of the side effects of damaged trap
seals include:
• Evaporation
• Capillary attraction
• Momentum loss
• Leakage
• Wavering out
• Compression of back pressure
• Induced siphonage
• Self-siphonage.
August 2017 Volume 23 I Number 6
Problems and causes
The general, functional requirements of
SANS 50858-1 states that “The design of the
separator system shall ensure that separated
light liquid cannot be discharged either
accidentally or in an uncontrolled way, for
example by syphoning. The design shall also
ensure that any separated and retained light
liquid is not disturbed.”
Capillary attraction is a rare occurrence, which
happens in S-Traps when a piece of porous
material is caught over the bend of the trap.
The material then absorbs water and deposits
it down the waste discharge pipe.
Momentum is caused by a sudden discharge
of water. Due to velocity, water is discharged
and it shoots around the trap bend and goes
down the waste pipe, leaving no seal.
Leakage is most often caused by a fault in the
trap or plumbing installation. Water would be
evident on the floor beneath the trap.
Wavering out is caused by the effect of
the wind, which passes over the top of
the ventilation pipe, resulting in pressure
fluctuations.
Compression in back-pressure usually
occurs in high-rise buildings. When water is
discharged down to the main discharge stack,
air is compressed at the base of the stack.
A waste pipe connected to the stack in the
pressure zone may have the seal of the trap
lost by the compressed air forcing out the
water. Detergent foam further increases the
risk of compression.
Induced siphonage is caused by discharge
of water from another sanitary appliance
connected to the same discharge pipe.
In either a vertical or horizontal main waste
pipe, as water flows down the pipe and
passes the branch pipe connected to it, it
draws air from it, thus creating a partial
vacuum and subsequently, siphonage of the
trap takes place.
Self-siphonage is caused by appliances,
such as wash basins and other small
appliances, due to their curved shape,
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