Newbie with a big problem

[plumbcrazy]

Hello all,

Thank you for taking time to help. I am faced with in my mind the impossible. A customer of mine needs me to increase water supply and demand without doing any type of piping. Here is the situation: You have a 10 thousand gallon storage tank with a existing 7.5 hp booster pump trying to feed a total of 1500 fixture units, with a total developed length of approximately 1600 LF of 1 1/2 PVC ran underground. What they are feeding is barns at a race track, and each barn has about 18 hose bib's and a total of four complete bathroom groups. Their reason for doing this is to get off the city water supply and get back on their well supply. I have offered variable speed drives, but my concern is that you can only push so much water through that size of line. I apologize for the stupidity I am spewing out here, but I can't wrap my head around this one. Am I off base by wanting to increase line sizes? Or is there something that could work here? Please help, I am desperate. Thank you in advance again.......

 

[quark]

If you know the flowrate required, a bigger pump can also be an option. Needs more data like present pump capacity, head, maximum consumption and average consumption etc.

 

[BigInch]

A larger pump, possible modification to the existing pump, or larger, or another pipe laid parallel, are the only alternatives we could suggest at this point... or probably ever.

The pipe system needs to be entirely identified.

VFDs can't increase the capacity, without overspeeding the pump you have now. Probably not the best idea to start with.

**********************
"Pumping accounts for 20% of the world’s energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies)

http://virtualpipeline.spaces.live.com/

 

[mtngreen]

Anything is possible with enough horsepower...provided you aren't above the pressure limits of the PVC pipe. Whats the gpm your trying to deliver?

How about installing some large expansion tanks in each barn?

 

[plumbcrazy]

Thank you all for the responses so far. As far as the existing pump goes, I do not have a lot of data on it, however what I do know is that they average about 20,000 gallons per day usage. What is hurting them is when all the guys come off the track and everyone is trying to water and wash down their horses at the same time, that is when the guy at the end of the run has barely a trickle. I wish I knew how many gpm's I will need, but for the most part eveything is on hose bib's. It is my understanding that the pump they have now does not do the job and is not working at this present time, I think they burnt it out because I believe that the tank is not filling fast enough and it ran dry. Thank you all again, I appreciate your helping.

 

[raronen]

I would develop an approximate "system curve" for all that piping. A system curve will have the equation y = mx^2 + b, where:
y is the head required
x is the flow rate
m is the friction loss factor in the sytem
b is the static head

So, you need to solve for m and b to know the curve. "b" is easy. You just figure out the elevation difference between the water level in the suction vessel and where water is discharging (plus the static system pressure if the pipes were discharging into a pressurized vessel). If the suction vessel level is higher than the outlets, this will be a negative number.

"m" can be more tricky. If you know the current flow rate, and the differential pressure of the pump, you can convert the differential pressure to ft of head and solve the equation for "m".

Alternatively, you can measure the length of pipe, count all the elbows and bends (being sure to note what kind of fittings they are) and use a reference like "Crane's Flow of Fluids" to calculate the total friction loss.

When you are done, you will see that the system curve is a parabola.

If you are currently operating where the curve is not yet vertical, a bigger pump will produce more flow. If you are operating where the curve has gone "vertical" you will need a huge pump to produce more flow, and you might create unintended problems like broken pipes. If this is the case, installing larger piping will almost certainly be cheaper than the big pump.

Once you have an idea of what the system curve looks like, your answer should be pretty straight forward. Good luck.

 

[BigInch]

mtngreen mentioned a tank near the barns. With high short-time flows, that might be your best option. You can fill the tank all night to have pleanty on hand for the washdown.

**********************
"Pumping accounts for 20% of the world’s energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies)

http://virtualpipeline.spaces.live.com/

 

[rzrbk]

You cannot increase the size of the piping, and the PVC probably limits the amount of pressure you can use to push more water through.

It sounds like you need to feed the existing system from multiple locations. An expansion tank (or a second pump) at the far end of the piping system would feed from both sides, effectively halving the peak flow thru the existing pipe system.

Mtngreen's suggestion of several smaller expansion tanks spread thru the system may be more cost effective way to handle peak flows.

 

[plumbcrazy]

Thank you all very mmuch for the replies, I appreciate it very much!

 

[SteveWag]

Is the existing city water supply doing the job? Where does the city system connect compared with the tank/pump connection? What is the city pressure at the point of connection?, during peak demand time? What size is the city meter and connection? Would it be possible to have access to the city meter during peak demand?

Steve

 

[zdas04]

If you go with auxillary tanks (probably a very good idea) with well water, you have to be really careful about water quality in the tanks. Well-water always has microbes that can grow pretty agressively in a standing body of aerated water. Just a thought.

David

 

[pmover]

perhaps installing a large expansion tank at the farthest distance from the pump. this will supplement the demand at the far end, but refilling the tank MAY take a long time as the pump will need to be capable of producing a discharge pressure to get water into the tank at such a long distance. maybe a small booster pump can be used to get the water into expansion tank, if time is critical.

how about installing low-flow nozzles to reduce consumption?

regardless, good luck!
-pmover

 

[wimple]

In Booster pumps water applications for example we usually consider pick and the fact that people consume water simulatneously (some coefficient is there to model flow capacity releated to habits of people...for example).

So the best approach is to have pumps in parallel if possible to gain in flexibilty and all equipped with VFD.

If you succeed to develop enough flow capacity, on the other side probably you will run overdesign of the pipe network size. That means even if your Pipe Nominal Design Pressure cover your duty, at least you will significantly increase losses and system resistance. Then typically you will also need to go with pumps with one size higher.

So in summary, if you have some margin with pipe design pressure, use higher sizer pump, VFD and eventually operates pumps in parallel.

I think there is some tradeoff between changing/improve or adding lines to pipe network (Capex) and keep network while runing with higher losses (Opex)..

Rgds
Wimple

 

[BigInch]

wimple,
Sorry, but you've got several problems you're ignoring.
The OP does not want to add pipe.
We already know that the system curve is maxed out, so how will another pump help that situation?
Its not people using water for domestic use; its at a race track, so use is not random.
How do you get more flow with a VFD? Is the VFD needed so you can buy a too big pump, then slow it down?

**********************
"Pumping accounts for 20% of the world’s energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies)

http://virtualpipeline.spaces.live.com/

 

[plumbcrazy]

SteveWag, that is the issue, they want to get off the city supply that they are on and put this section of the property back on the well side, it just gets too expensive for them to be on the city water. You guys are absolutely incredible, and I thank you for all your input! All these suggestions are very worthy of exploring.

 

[IFRs]

Can you reduce the flow through the early outlets so the last one still has enough?

 

[wimple]

BigInch

The suggestion was to increase flexibility in order to accomodate variable demand/consumption. Maybe I did not get it means the demand is stable?

So if the point is only increase capacity from Flow A to Flow B. Then you could keep same pump size and use VFD (I think appropriate only for moderate increase of flow)

In case jump of flowrate is significant, I suggest to add pump in parallel then either combine with VFD or increase pump size as you need to have a single pump operating at the right of BEP.

In any case, the Pump discharge head will increase.

As there is constraint with pipe size because they dont want to change it, they you check if they have some margin with actual pipe design pressure. I think it is the limiting factor, dont you agree?

Rgds
Wimple

 

[wimple]

quoted 'In case jump of flowrate is significant, I suggest to add pump in parallel then either combine with VFD or increase pump size as you need to have a single pump operating at the right of BEP. '

sorry I meant at the left of the BEP

 

[TBP]

We did work in a small, relatively new plant that had the same kind of problem. Their "solution" was to jack-up the inlet water pressure to whatever they had to. The water velocity was nothing short of spectacular. This, combined with the fact that the construction contractor didn't bother reaming any of the copper pipe, combined to have 3/4" 90* els lasting as little as 6 months.

 

[BigInch]

Tank.

**********************
"Pumping accounts for 20% of the world’s energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies)

http://virtualpipeline.spaces.live.com/