Force Main Bypass 2

[LaurieL]

An existing forcemain requires maintenance in several areas. We wish to reuse an abandoned forcemain as an emergency bypass during inspection and repair of the existing forcemain. The issue is this: we want to tie the two together and the lift station and again just before the lagoon and be able to switch from one to the other. Being pressurized, can this be done? What sort of valving would be required and who should I contact (in Canada). Once repairs are complete on the existing line, we do not foresee ever using the bypass again (hopefully).

 

[semo]

It can be done in several manners.

Depending on pipe size and manner, it can also get very expensive. You can tie the two forcemains (fm) together hot with a tapping tee and valve, then use install an insert valve (with line stops) or a temporary line stop in the existing fm downstream from your tee to shut off the existing fm. In large sizes the tapping tees can be pricey; but, the insert valves/line stops are really pricey.

If there is time between pump cycles you can look at using a cutting in sleeve with tee and valves in lieu of an insert valve.

For time you can also use a bypass pump connected to the backup fm while you make taps to the existing fm. Then switch back to the existing fm while you connect the bypass fm.

Do you have to connect the two fm's at the lagoon? Can you extend the bypass fm into the lagoon?

There are a lot of options (more than I mentioned here), just depends on how permanent you want things and how much you want to spend. I gave some ideas where you can start.

 

[KRSServices]

I would advise caution on this one, for several reasons.

1) Why the forcemain originally abandoned? Was it due to sizing, material deficiency or age (high maintenance costs). If you are inspecting the new line, I used to hire large vac truck (tri-axle units) to evacuate effluent out of the wet well (through an attachment and through the overflow). This works very well for a short term duration.

2) Is the abandoned forcemain rating compatible with the pressure output of the lift station, particularly near the station where the pressure should be the greatest.

3) Examine the costs of implementation of putting the abandoned line back into service (after evaluating item #1 above) and the continuing costs of operating the existing line. The numbers may suggest that the existing line may require replacement of entire sections or in it's entirety rather than the option written about.

4) Lastly, you should look at the ramification of the overall reliability of the system, as presented in your thread. If either of the new or abandoned line "pop" what are the backup systems in pace? If the lift station is in a residential area, or near a body of water, and an overflow spill occurs, what are your policy responses? The answer may entail a review of the line system, to the point where some replacements as stated in item #3 is required.

KRS Services

http://www.krs-services.com

 

[LaurieL]

Thank you for your responses.

The active forcemain that requires repair is PVC, 450mm in diameter and 3.5km long. It was designed to service an anticipated growing population that never materialized. It replaced a 300mm diamter AC forcemain. Would it be more feasible to just bypass the known problem area and ignore the abandoned forcemain altogether? This is a remote community, next to a body of water with limited funding. The cost of standby pumpers is obscene.
How about building a bypass forcemain next to the problem area and valving into the problem section of the active fm then abandoning that section?
Tying into the abandoned forcemain at the lift station and then again at the lagoon does allow for a thorough CCTV of the active forcemain. It also allows for an alternative route to the lagoons should any further problems occur. Past breaks have run into the body of water causing environmental problems. Capacity is adequate with only minimal repairs required. It's a dilemma.

 

[KRSServices]

lauriel,

Thank you for your reply. I agree that in this case, evacuation of the wet well via pumpers may be a high cost.

Is the area in question 3.5 km or the total length of the forcemain 3.5 km? I ask because you repeatedly stated "problem area" with reference to the forcemain. Why is this section seemingly problematic? Is it due to the number of breaks or ruptures? Are the soils poor? Is there an undue amount of hammer?

Also in this section, how did the AC pipe perform? Assuming that the gradient of the pipes are similar, how did it perform over time?

My first response to your query remains the same, however. In my item #3, I made reference to undertaking a cost analysis into the options, which would include reconstruction/upgrade requirements and could be done in conjunction with a demand/audit. Realizing of course that the community may not have a large budget, there are other possibilities that may not be too costly which can be considered.

Is this a Canadian jurisdiction (your reference to km's)? If so, I have been quite successful at the Provincial level of acquiring cost shared arrangements for projects similar to yours. Having said that, I still believe it is premature to begin talks of funding when the analysis hasn't been completed yet.



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