# HELP - Test question with no answer! ERRRRRRR



## SCPE (May 25, 2012)

A 10 ft diameter pump station has a 15 minute fill time. If maximum of 3 pump starts per hour is desired, what is the minimum distance between the pump on and pump off elevations?

A. 1.6 ft

B. 2.6 ft

C. 3.6 ft

D. 4.6 ft

*You need the pumping rate correct to solve??? They dont give you enough info!!!!!!!!!!!!!*


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## SCPE (Mar 6, 2014)

Guys - I posted this two years ago and have yet to find an answer. Anyone want to take a shot?


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## Mike in Gastonia (Mar 7, 2014)

SCPE said:


> Guys - I posted this two years ago and have yet to find an answer. Anyone want to take a shot?


Perhaps everyone is concerned that this was a question from an actual exam you took and don't want to get in trouble. Where is this question from?

Secondly, it might help if you put it in the exam sub-forum for your discipline. This sub-forum is more for work-related questions...........


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## Dleg (Mar 7, 2014)

It would seem like you need a pump rate to answer. I agree.


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## SCPE (Mar 7, 2014)

This was from a practice test. So I am not crazy after all.


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## ptatohed (Mar 9, 2014)

SCPE said:


> Guys - I posted this two years ago and have yet to find an answer. Anyone want to take a shot?




SCPE, I think you would have seen more response to this exam prep type question if you had posted in this forum. It does seem some info is missing. What is the answer and do you have the solution?


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## SCPE (Mar 24, 2014)

ptatohed said:


> SCPE said:
> 
> 
> > Guys - I posted this two years ago and have yet to find an answer. Anyone want to take a shot?
> ...




I dont the answer. Its supposed to be one of the 4 options but as others stated, it seems like its missing info.


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## Lumber Jim (Apr 3, 2014)

SCPE said:


> A 10 ft diameter pump station has a 15 minute fill time. If maximum of 3 pump starts per hour is desired, what is the minimum distance between the pump on and pump off elevations?
> 
> A. 1.6 ft
> 
> ...


Since they do not give a flow rate for the pump and the height of the pump station, the minimum distance for the choices given is most nearly: A. 1.6 ft.


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## ptatohed (Apr 7, 2014)

Okay, how's this?

I don't know why I do this but I spent half my lunch hour on this.

Searched the internet and it seems that for a 10' diameter pump station, the typical pump station length/height is approx 50'. So, we need to make one assumption: h = 50'

Per this document here (seems like a nice source of info on pump station design), page 11:

Δh = V/wet pit area

Δh = (pi r2 h) / (pi r2 + 2 pi r h) = 5h / (2h + 5) = *2.4'* *Answer B?*

In fact, if this is a correct approach, a fairly wide range of h's will still give you 2.X ft, so the problem isn't requiring you to make a completely unrealistic assumption to solve given only the diameter. What do you guys think?


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## ptatohed (Apr 21, 2014)

ptatohed said:


> Okay, how's this?
> 
> I don't know why I do this but I spent half my lunch hour on this.
> 
> ...






It's been 2 weeks. Any comments on my half-baked proposed solution?


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## IlPadrino (Apr 23, 2014)

ptatohed said:


> What do you guys think?




I think "wet pit area" isn't analogous to wetted perimeter, but rather simply the area of the wet pit. If so, the formula "Δh = V/wet pit area" is trivial and doesn't help.


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## Predgw (Apr 24, 2014)

If they gave you a height, then you would be able to solve. However, making that assumption seems odd in a problem. If this is a practice problem, I would throw it out and spend the time more wisely on problems of the same concept, but with answers.


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## Lumber Jim (May 6, 2014)

I'm still stuck on the fact that the station takes 15 minutes to fill (assuming empty to full) but you only want to start your pumps every 20 minutes (max) Sounds like some civil engineer overseeing the completion of the project should be wearing hip waders when the station is inspected at full capacity...

And shouldn't have listened to the town mayor trying to cut cost for his constituents...


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