Pump Station

[Brian]

With respect to separate contributory sewersheds, is it safe to assume different peaking factors for each specific sewershed when sizing a pump station?

I am currently designing a pump station to replace to existing two pump stations. One PS serves a minor league baseball park (4 months of operation per year), and the other serves existing sanitary sewer. I am calculating flows at the ball park with a peaking factor of 10, and the existing sanitary with a peaking factor of 4. I have detailed flow data for each sewershed for the past 2 years for the ball park, and 3+ for the existing sanitary. Am I correct on this approach, or should I combine the flows and assume one single peaking factor - for example, 6.

Brian

Sweetland Engineering

 

[Art]

what is the capacity and daily run times for the existing pumps?

this will be the best indicator of how to size the new one...

or check the runtime against a day of high rainfall...

if say one pump only runs 2 hours per day, average flow...that's a duty cycle of ~12%...it's probably over sized...a good number to shoot for is 25%...

or it runs 6 hours on a rainy day...df ~25%, still over sized...50% on a peak day is not bad...

depending on wet well size, it should be sized for a normal retention of 30 minutes or so...

that means the pump runs 4 out of every 30 minutes...so you could have 7 times as much flow and still keep up ~30/4 ~7....

another way to use those numbers:

say your pump is rated at 100 GPM (check amps (HP) vs curve to get the rate)

and it runs 2 hours/day, it's pumping 120 min x 100 gal/min ~ 12,000 gal/day

let's say on a high flow day 12 hrs is acceptable...720 min 100 gal/min ~ 72,000 gal/day...

you don't want the pump too big...

intial cost

could have too many starts per hour, this is based on HP and motor type...in this case it starts 1/30 min or 2/hr, that's good...

PA DEP says use 250%...

but depending on how the flow is calculated, it's still usually too much..EDU's are always over estimated...

DEP says 400 EDU or 265 (2.65 people/house x 100 gal/person)...water records show it closer to 170 gal/day per EDU...

so it's inherently oversized to begin with...

then when selecting a pump people usual go to the next impeller on the curve, so more margin...

by the time it's all said and done you have a pump that runs 5 hours per week, and septic sewage...I've seen it many times...

bigger is not better...

remember, the wet well gives you a buffer & storage capacity

and as the wet well level rises th pump can pump more due to higher positive suction head...it can be substantially moe depending on the curve...

also set the controls up to alternate and lead-lag...so if the well rises, the 2nd pump kicks on....

depending on the force main size, you won't get double the flow, but maybe 50% more...

I know, I rant, but I came from a process background into the sewer world, and it kills me how you 'civil' guys do things

 

[Brian]

what is the capacity and daily run times for the existing pumps?this will be the best indicator of how to size the new one...

or check the runtime against a day of high rainfall...

if say one pump only runs 2 hours per day, average flow...that's a duty cycle of ~12%...it's probably over sized...a good number to shoot for is 25%...

or it runs 6 hours on a rainy day...df ~25%, still over sized...50% on a peak day is not bad...

depending on wet well size, it should be sized for a normal retention of 30 minutes or so...

that means the pump runs 4 out of every 30 minutes...so you could have 7 times as much flow and still keep up ~30/4 ~7....

another way to use those numbers:

say your pump is rated at 100 GPM (check amps (HP) vs curve to get the rate)

and it runs 2 hours/day, it's pumping 120 min x 100 gal/min ~ 12,000 gal/day

let's say on a high flow day 12 hrs is acceptable...720 min 100 gal/min ~ 72,000 gal/day...

you don't want the pump too big...

intial cost

could have too many starts per hour, this is based on HP and motor type...in this case it starts 1/30 min or 2/hr, that's good...

PA DEP says use 250%...

but depending on how the flow is calculated, it's still usually too much..EDU's are always over estimated...

DEP says 400 EDU or 265 (2.65 people/house x 100 gal/person)...water records show it closer to 170 gal/day per EDU...

so it's inherently oversized to begin with...

then when selecting a pump people usual go to the next impeller on the curve, so more margin...

by the time it's all said and done you have a pump that runs 5 hours per week, and septic sewage...I've seen it many times...

bigger is not better...

remember, the wet well gives you a buffer & storage capacity

and as the wet well level rises th pump can pump more due to higher positive suction head...it can be substantially moe depending on the curve...

also set the controls up to alternate and lead-lag...so if the well rises, the 2nd pump kicks on....

depending on the force main size, you won't get double the flow, but maybe 50% more...

I know, I rant, but I came from a process background into the sewer world, and it kills me how you 'civil' guys do things

'US' civil guys? Ok I see how you are... lol

Thanks the the rant - I can work with that.

Brian

 

[WAHOO-LONGHORN]

I am looking at a very similar job from a review/clean up perspective. We have an existing station at a retirement home which is sized for ultimate development which never happened. Our client bought land from the old folks home and is building an intercollegiate sports facility there. We're looking at flowing into the existing station and using an EQ tank. The prime AE used a peaking factor of 5 for the new sports facility. I couldn't see the purpose of this high peaking factor. To me, it seems prudent to use the MDE generated flows and then peak them by three at the most. The controlling factor at a sporting event is fixture count and rarely would you experience huge I&I during a game (because there would be few spectators).

As far as pump utilization goes, we use an equation from MDE to provide 7 minute minimum cycle times.

Just my 2 cents.

 

[Art]

'US' civil guys? Ok I see how you are... lol
Thanks the the rant - I can work with that.

Brian

just some friendly rivalry

like you guys don't think us electricals are strange

 

[Guest]

just some friendly rivalry
like you guys don't think us electricals are strange

I actually would have liked to have had some coursework that was more suitable to sizing pumps while in school that focused more on the mechanical and electrical aspects. I don't find it strange at all .. but then most people DO find me strange ... :blink:

JR

 

[Brian]

just some friendly rivalry
like you guys don't think us electricals are strange

You're right - we do think you're strange... lol... but you provide my pumps backup power - which I thank you for.

Brian

 

[Brian]

Another question - Estimating peak flows - the only data available if water usage data for specific buildings contributing to flows at the pump station. Also, currently there is no meter at the station, and run times are not available for the pumps.

Besides the Ballpark, which really does not contribute all that much, the only thing to really go on is monthly water usage data - basicaly all water going INTO the buildings for use.

Why there is so little data from the PS to go on, I do not know. But that's not my problem right now.

thanks for any light someone can shed on this.

Brian

 

[DVINNY]

I think Art hit on it in his first post, if you have an existing PS there, or two of them, then do drawdown tests on the existing systems. That will tell you what you need to know.

Since there is probably no games this time of year, do as he said, and go out on a rainy day (after it's rained for a while) and get a drawdown for a few cycles.

That should tell you how much flow actually goes through those pumps under the different circumstances, peak and normal.

my two cents from a mechanical/civil guy.

I too wish I knew more about the electronic end of them, because in the past, I've gone off of recommendations from suppliers about controls, etc. for lift stations, and that can get you burned. I don't have a good electrical guy in my office, and we need one.

I know enough to look at the poles around the area and determine if I have 3 phase nearby or just single phase, etc. Other than that......... ughhhh

 

[Brian]

I think Art hit on it in his first post, if you have an existing PS there, or two of them, then do drawdown tests on the existing systems. That will tell you what you need to know.
Since there is probably no games this time of year, do as he said, and go out on a rainy day (after it's rained for a while) and get a drawdown for a few cycles.

That should tell you how much flow actually goes through those pumps under the different circumstances, peak and normal.

my two cents from a mechanical/civil guy.

I too wish I knew more about the electronic end of them, because in the past, I've gone off of recommendations from suppliers about controls, etc. for lift stations, and that can get you burned. I don't have a good electrical guy in my office, and we need one.

I know enough to look at the poles around the area and determine if I have 3 phase nearby or just single phase, etc. Other than that......... ughhhh

Thanks - I'll give that a shot and see what happens.

Brian