System Curve for Booster Station Pump Selection 1

[TJH2161]

I am trying to develop system curves for a booster station that got destroyed during Hurricane Ida. We need new pumps as the old pumps were inundated with salt water and received some wind damage. I've read some previous posts that were very helpful about developing a system curve for a booster station where tank levels vary, which is the situation I am currently looking in to.

When doing so, my "low end" system curve is very low, i.e. 500 GPM @ 1.8 feet of head. This curve was developed based on a low flow event, downstream tank empty, and suction pressure at the booster station basically equivalent to the pressure at the downstream tank. I know the head sounds low, but keep in mind that we have 18", 14", and 10" waterlines in parallel feeding the downstream tank.

My "high end" system curve is 1 MGD @ 71 feet of head. This curve was developed on a high flow event, where the downstream tank is full, suction pressure at the booster station is at the preset shut off pressure of 30 psi, and water only goes through the 14" and 10". I did this because there are times where the 18" line is closed off so we can push more water through the 14" and 10" line to increase chlorine residuals.

I guess my main point in posting is trying to get some feedback from some experienced engineers on if you've seen situations like this? Is this wide of a range for the system curve common for booster stations?

 

[LittleInch]

You confused me by the different units. 1MGD = 694 GPM? so not a big turn down in flow??

Normally you would look at the low head end of only flowing the 10" line to not have this almost negligible head loss.

when you have different options of three lines then you will either end up with so many different lines you won't see anything or have different lines on different graphs.

You need to understand how often each applies to the system to determine a "normal" flow and differential head and what you can do for the other options. Types of pumps would also make a big difference.

for the low head options could you flow faster but for a lower time duration?

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[TJH2161]

@Little Inch, thank you for your response.

For low flow events on a normal basis, its not really practical to say we will only flow water through the 10". The amount of manpower it would take to manipulate valves along the 32,000 linear feet of waterlines to the downstream tank is not practical. We might isolate lines twice a year, and the rest of the year all three lines are open. But you bring up a good point that reflects on what I believe is an issue for us, which is having these three lines in service. Realistically the 18" line is more than capable of carrying the water we need to these areas, but no one likes to discuss the options of abandoning existing lines as they like the redundancy in the system.

 

[bimr]

I guess my main point in posting is trying to get some feedback from some experienced engineers on if you've seen situations like this? Is this wide of a range for the system curve common for booster stations?

No, your scenario with the multiple pipelines is not common. Why don't you replace the pump in kind? What the previous pump meeting your capacity requirements?

 

[LittleInch]

So long as you mothball them correctly or change over on a regular basis, you shouldn't have to abandon them...

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[1503-44]

Hydraulically that is equivalent to many systems. A pretty common example might be a single pump, or pump station that has to pump different products to tanks all over a tank farm each tank being connected to the pump discharge header with separate pipes, each pipe of different lengths and diameters. That problem is equal, if not very much more, complex. put each tank at different elevations going up the side of the hill that the tank farm is built on and you can have nearly an infinite number of system curves. Then give a different minimum and maximum flow rate allowed for filling each tank. Add a heavy or waxy oil and system curve varies with tank temperature and the temperature profile along the pipe at any given time. Now only allow some products to go into the low tanks, others that can only be stored in the highest tanks. Put some heavy oil at the farthest and highest tanks just to get the greatest pressures possible.

 

[TJH2161]

@bimr We may replace in kind, we were just looking at a few different scenarios for the future and thought that having pumps with additional capabilities might be better than the existing pumps. That's why my system curves vary so much. We looked at different scenarios that we haven't really taken into account in the past.

 

[Artisi]

Did the original "system" operate successfully, if yes why not consider duplicating the pumps, although a review of the operation may have some merit.

I don't see why salt water and wind damage (what ever that is) is a reason to right-off the original pumps.

It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)

 

[bimr]

How many pumps do you have?