Профессиональное развитие будущих инженеров-строителей средствами иностранного языка: Лексический практикум по английскому языку. Трубникова Н.В. - 76 стр.

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76
Loss of water seal from a trap can occur through the following mecha-
nisms:
1. Self-syphonage: this can be avoided by placing restrictions on
lengths and gradients and venting long or steep gradients.
2. Induced syphonage: water flow past a waste pipe junction in a stack
or along a sloping horizontal range of appliances can suck out the water seal.
This is overcome by suitable design of the pipe diameters, junction layouts
and venting arrangements.
3. Blow-out: a positive pressure surge near the base of a stack could
push out water seals of traps connected in that region. Waste pipes are not
connected to the lower 450 mm of vertical stacks, measured from the bottom
of the horizontal drain.
4. Cross-flow: flow across the vertical stack from one appliance to an-
other. Waste pipes are not connected to soil and vent pipes where cross-flow,
particularly from WC branches, could be caused.
5. Evaporation: this amounts to about 2.5 mm of seal loss per week
while appliances are unused.
6. Wind effects: wind-induced pressure fluctuations in the stack may
cause the water seal to waver out. The vent terminal should be sited away
from areas subject to troublesome effects. Wind-tunnel tests using smoke as a
tracer are performed for large developments.
7. Bends and offsets: sharp bends in a stack can cause partial or com-
plete filling of the pipe, leading to large pressure fluctuations. Foaming of de-
tergents through highly turbulent fluid flow will aggravate pressure fluctua-
tions. Connections to the vent stack before and after an offset equalize air
pressures. A bend of minimum radius 200 mm is used at the base of a soil
stack to ensure constant ventilation.
8. Surcharging: an underground drain that is allowed to run full causes
large pressure fluctuations. Additional stack ventilation is required.
9. Intercepting traps: where a single-stack system is connected into a
drain with an interceptor trap nearby, fluid flow is restricted. Additional stack
ventilation is used.
10. Admission of rainwater into soil stacks: when a combined foul and
surface-water sewer is available, it is possible to admit rainwater into the dis-

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