sewer bypass pumping

8/12/2019 Sewer Bypass pumping

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Introduction :

With the passage of time our sewer ’s structure needs rehabilitation and repair to keep them up and

sufficient for the communities that count on it. Dealing with the aging problem of underground structure

is a main concern of many cities and sanitary sewer. (1)

The most important part of the rehabilitation is the design and construction of effective temporary by-pass

pipe line system to convert flow from the sections of a pipe which is under rehabilitation or replacement

and keep the service for the residence and businesses during the construction without any interruption.

For the projects which have the large-diameter pipes, bypassing by itself is a vital project. “Depending on

the nature and scope of the project, bypass pumping can be relatively easy or extremely difficult and

complicated,” said Lynn Osborn (senior applications manager for Insituform Technologies, a leading

worldwide provider of proprietary technologies and services for rehabilitating sewer, water, energy and

other industrial pipelines) (1)

“For small sewers, the flow is often plugged or handled with one small pump,” Osborn continued. “As

pipe diameters and flow rates increase, bypass pumping can become one of the most complex and costly

components of the project, especially when flows can exceed 100 million gallons per day. (1)

“However, the importance of bypass pumping is always critical because sewage overflows or spills, large

or small, can cause significant project consequences, social impact and/or environmental damage.” (1)

The core of bypass system is a pumps and equipment that many of companies have designed them to

meet the bypass demands .there are some manufactures that provide these equipment5s and pumps on a

rental bases. (1)

Figure():bypass pumping (2)



Objective

To get and spread working knowledge of Bypass pumping

Project Scope and LimitationsThe Scope of the project is:

To know what is bypass pumping where, why and when bypass pumping is used Aspects of Sewer bypass pumping are included in the study

The project is limited to:

This project do not include the in-depth knowledge of design of pumps and its components Bypass pumping in water mains rehabilitation work is not included

Importance of bypass pumping Bypass pumping is a critical element of many rehab projects. Temporary bypass systems are used totransfer water supplies and sewage flow, so that these vital services are uninterrupted duringconstruction. http://www.griffindewatering.com/dewatering/bypass.html#.U4axtfldVps

When a sewer line is subjected to rehabilitation works, sometimes the flow of sewage cannot simply bediverted; it must be bypassed or temporar ily pumped around the pipe being repaired or replaced. It’svery important to keep in mind the location of the city (i.e. residential, commercial or industrial). To dothis, pumps capable of pumping trash- and sewage-laden effluent are used.

I n Sewer li nes:

In sewer line when there’s a rehab project is carried out it’s necessary to pump the sewer across the

activity boundaries downstream and release it to reduce the obstacle of sewer water passage during

rehab operation and to stop the waste to spill over the road and causing nuisance to the public around

that area. The sewer water may cause spread of disease and harm the inhabitants of the area where the

activity is going on. For this purpose it’s very important to bypass the sewer and stop it from spilling over

or moving through the activity boundary.

I n li ft stations:

There are many reasons for bypass pumping in lift stations such as aging, new construction ,lift station

recovery (they are facilities which is used to convey water from lower level to higher one within the

pipes),lift station out of order or malfunctioning, separation of force mains or any combination of these

factors. (3)

http://www.griffindewatering.com/dewatering/bypass.html#.U4axtfldVps






Bypassing sewage is important because without any treatment it can result in the discharge of sewage into

rivers so the harmful bacteria and some chemical toxins will increase than their normal level and it can

impact downstream communities and wildlife. Here is a table which is comparing total volume of treating

sewage and the ones without any treatment in London city. (4)

As it is clear in the above table for example the city of London treated more than 75000 million liters for the

sewage and also there were 58 by-pass events without any treatment which is caused 225million liters of average

daily flow of sewage goes into the Thames river. (4)

Pumping Activity (I gave a general idea here if you find it interesting then we can tell others)

Although there are many different techniques fordoing temporary bypass pumping, the techniquesvary from contractor to contractor. Generally, a

pump or set of pumps that are adequate to bypassthe maximum flow of a sewer line which is subjectedto rehab/ inspection are placed and a system is madeto bypass sewer from upstream and across the pipe

which is subjected to inspection or rehabilitation tothe downstream line leaving it dry. For this purposeafter the system the pipe is blocked temporarily withthe help of plugs and the sewer bypass begins andcontinues until the assigned activity is done on the

pipe and the pipe is free to pass the sewer again. http://www.aquatechdewatering.com/how_do

_you_do_that_article.php?Design-a-Bypass-Pumping-System-4 image reference

http://www.aquatechdewatering.com/how_do_you_do_that_article.php?Design-a-Bypass-Pumping-System-4









Pumps and equipment:

Practically all bypass processes can be done and accomplished by use of wide variety of bypass

equipment such as pipes and pumps.

Practically piping is HDPE, Ductile iron or PVC are allowable .Hoses should be of rough construction

and valves normally must be of a type that stops trash in the sewage from twisting on obstacles. Typically

centrifugal pumps are used in this regard.

Pumps are the most important part of the bypass process and all of them are guaranteed by the laws of

physics. At sea level the theoretic maximum suction lift for water (it doesn’t matter if it is self-priming or

vacuum assist) is 33.9 feet.

There are some factors that can limit the pumps to a practical lift of less (25 to 28 feet), so that’s why we

need specific type of pumps which is called submersible at deeper settings. There is no limitation for them

in suction lift. Bypassing with suction lift of less than 25 feet and above the ground are accomplished by

prime-assisted pump. Self-priming or prime-assisted pump. There is a factor which is calls NPSHRA

which is stand for Net Positive Suction Head Available. This factor plays an important role in the proper

pump selection. (5)

Centrifugal Pump

It is a pump that is used centrifugal force to improve pressure (6)

The centrifugal pump increase force by shifting mechanical energy of the motor to the fluid with rotating

impeller.

The force of centrifugal pumps increase the speed of fluid and then dynamic energy is transformed to

pressure.

Just to understand it better, imagine you are drinking water by a straw .You create a vacuum in

the straw and the fluid rise up because of the atmospheric pressure but even under the best

condition you cannot lift the water more than 33.9 feet. If you stand on a four-story building and

you have enough straw long it will not rise more than 33.9 feet. That’s why you need an extra

pressure. (7) while giving example I think it is not good to use you/I in a project report.



There are some pros and cons about centrifugal pumps. In this case, suction hoses are available through

almost all the openings, furthermore it can be used in parallel or in series but you have to keep in mind

the prefers capacity in gpm (normally it is predetermind) and also net positive suction head (3)

Pumps in Parallel:

It is important to know that peak flow can easily become more than the capacity of any pump, so multiple

pumps in parallel are required. Discharge heads can also exceed the maximum capacity of pump which

would require pumps in series. (3)

Pumps in series:

In this category you have to use two or more pumps at the same time. There is a connection between the

first pump discharge and the second pump suction so it can make more head pressure by each pump thisis not usually recommended for sewage because if one of the pumps fail you cannot discharge to the

chosen point. (3)

FIGUER (): CENTRIFUGAL PUMP (6)

What are submersible pumps ? Submersible are kind of centrifugal pumps with a motor that is attach to it and are flooded in the sewage.

They are commonly electrically driven but in some cases you can find them hydraulically driven by a

power pack which can be motor or diesel. (3)



Figure (): submersible pump (3)

There are some advantages about submersible pumps .for example by submersible pumps you have

constant priming and also there is no limitation for suction lift but on the other hand you have some

disadvantages .for instance It cannot be accessible from most of the opening because of the physical size

and their weight, They must be removed for cleaning the thrashers that stuck in the impeller, If there is no

electrical power around ,you need to use generator, Submersibles need a special amount of submergence

on the volutes for operating correctly and for cooling the motor, so they need NPSHA, but it is not as

dangerous as the above – ground centrifugal. (2)

There are some factors that when you use this kind of pumps you have to be aware of them:

1. Peak flow rate in GPM

2. Statics discharge rate: vertical distance from fluid to the pint that you discharge

3. Size, length and type of piping and fitting (3)

sewer bypass pumping

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