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Them on Diffuser Effluent Outfall Lines) |
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''Diffuser Effluent Outfall Systems'' that do
not have ''Back Flow Preventers'' face serious
problems, the most important of which are described
hereunder.
These problems could be avoided with the use
of Tideflex® diffuser check valves.
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Principle of operation: |
| Minimum internal pressure opens
the valve, while, |
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Minimum back-pressure closes
the valve tight |
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Piles of Sand, Silt and Stones:
In Outfall Systems without Check Valves, wave
action over a period of years results in stone
and sand entering the system and creating high
piles of stone and sand underneath each nozzle
opening. The stone piles restrict the flow even
more than 50%. Along with the flow restriction,
the stones and silt act as a filter for the effluent
resulting in the stones becoming toxic.
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Marine Growth Intrusion:
Without ''Back Flow Prevention'', critical intrusion
of marine growth inside the outfall pipe takes
place. This problem alone justifies the use of
TF-2 Diffuser Check Valves.
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Outfall Lines Require Costly Flushing: |
| Without ''Back Flow Prevention'', outfall lines require
periodic purging or flushing to stay clear, often requiring
extensive diving operations. Cleaning is time-consuming
and clean up cost is excessive, as, besides build up of
stones and silt, there is a large amount of marine growth
blocking the flow. |
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Saline Intrusion: |
| During low flow conditions, salt water enters the diffuser
system, if Diffuser Check Valves are not provided. Because
of the higher specific gravity, the salt water intrudes
and forms a saline wedge on the bottom of the pipe.
Salt water can block a number of ports, which will
upset the internal hydraulics and reduce the dilution
efficiency of the diffuser. This can block up to 20%
of the flow of effluent in the system. When the volume
of effluent from the sewage treatment plants increases,
at high flow conditions, the hydraulics are often such
that, increased flow volume at gravity pressure is not
enough to expel the seawater.
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Salt Water Purging: |
| Purging salt water from conventional diffusers often
requires flows near the peak capacity of the plant. Tideflex®
fitted diffusers purge salt water at very low flow allowing
the diffuser to perform efficiently. |
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TF-2 Diffuser Check Valves Enhance Jet Velocity: |
| The benefits of using the TF-2 engineered
Check Valves is they enhance initial dilution. The restriction
induced by the TF-2 Check Valve at low flow, increases
velocity of the jet stream which improves initial dilution.
The TF-2 Check Valve creates an elliptical (flattened)
plume which has larger surface area than a circular plume
of a pipe nozzle, also enhancing near field mixing. TF-2
Diffuser Check Valves also enable more uniform flow through
each nozzle, as opposed to higher flow through the first
five or ten nozzles. This is similar to putting your thumb
at the end of a garden hose. |
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Hydraulic Transients: Reverse Differential Pressure Causing
Reverse Flow: |
| Pumped outfalls can experience pressure transients when
pumps are turned on and off. This can result in ambient
seawater, sand, silt, etc. to be drawn into the outfall
through the ports. Tideflex® Check Valves prevent
intrusion during hydraulic instabilities.
This was not known until videos showed a Tideflex®
check valve in an extremely ''sucked in'' position following
a power failure. It was obvious in seeing these videos
that, had they not installed a Tideflex® Check Valve,
large quantities of salt water, sand and debris would
have entered the system.
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Ocean Wave Action: |
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An existing diffuser system with TF-2 check valves,
at a location in northern Spain, is subject to 50' waves.
On the ''Down Swing of the Wave'' the check valves get
pushed down on (i.e. ''partially'' sucked in). On the
''Upswing'' the 50' wave force creates a suction effect
and pulls a tremendous amount of effluent out of the
system. During low flow, the pulling force of large
quantities of effluent causes problems by creating air
pockets, resulting in water hammer.
Initially it was planned to remove one of the check
valves allowing seawater to go into the system to prevent
the air pockets. Finally, it was decided to install
a check valve in the reverse direction to permit seawater
to go into the system. This was a better solution, as,
during the times when there are no 50' waves, seawater
will not be going into the system through an open pipe.
Seawater going into the system will only occur when
50' waves create air pockets. Even though this is an
extreme condition (causing air pockets), all diffuser
systems subjected to ocean wave action and without Diffuser
Check Valves fill with sand and stones.
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Outfall Lines as a Standby: |
| Building a large, ultramodern sewage treatment plant
often leads in abandoning the old diffuser pipeline system.
However, since the diffuser pipeline system represents
a huge investment, it is preferable to keep the old diffuser
system on stand-by, in the event of an emergency breakdown
at the sewage treatment plant. This means that the system
should be clean for an emergency discharge situation.
TF-2 Check Valves are the best solution for
this purpose and have been adopted by the City of Hong
Kong. |
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Vacation Beaches: |
| Many outfall lines are installed in cities and towns
that depend entirely on the tourist trade for their livelihood.
In many of these towns the population increases 4-10 times
the normal winter population. During low flow conditions,
in the winter, salt water and other debris enter the system. |
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Small Costs of Diffuser Valves: |
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The small additional
cost for Diffuser Check Valves to overcome all of
the above ''Real Problems'' represents no more than
a 2% additional cost of the overall project.
The savings that result from avoiding the problems
stated above far outweigh the relatively small extra
initial cost of installing Diffuser Check Valves.
Furthermore, the TF-2 Diffuser Check Valve is an
all-elastomer product, without any moving mechanical
parts, and, as such, is not subject to corrosion.
No other valve fulfills both of these requirements,
making it ideal for underwater service.
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Tideflex®
Effluent Diffuser Check Valves 
