Water supply system steep vs flat curve

[desann]

Hi. this is a follow up on my previous post. I think it would be better to make a new thread because there is a clear, specific question now.

My project is about supplying water to our fogging system which is basically another pump and also end user flow.

The requirements from the device's manufacturer are 12 m3/hour at 3-4 bar. However real flow at which is the system operating is 4 or 8 m3/hour, depending on whether single string is on or both. Please note, that the flow is always restricted to 4 or 8 m3/hr by the system.

I would like to use 2 pumps in series of which the second pump is supposed to be Ebara either Matrix or 3M. First pump will be submerged in the water tank, supplying Ebara which is supposed to act as a pressure booster. The supply line will be regulated by VFD and pressure control loop. There will be a pressure tank and high flow filter unit in the system.

Please find below our system curve along with the pump characteristics. The dotted lines, barely visible are standalone pumps, the bold lines are pumps in series and system curves.
I created system curves for 3, 3,5 and 4 bar that is a range required for the end user. Also I created the characteristics for 10 and 20% speed reduction.

I can see that the Matrix pump has a much steeper line than 3M. By looking more closely I would say by going for the "steep" pump it will need more precise speed tuning but I can get the output want.

Also important to mention,the steep one is significantly cheaper.

I would be very interested in getting a more detailed view what are the real advantages and disadvantages of both solutions and which one fits our system better.
Due to the lack of practical experiences I cannot predict that, so I would like to ask you for advice. Is it all about the VFD setting and fine tuning in my scenario or do I miss something?







Thank you.

 

[goutam_freelance]

Too many curves and legends. It will be helpful to show only a) Single pump characteristics b) combined pump characteristics. c) system resistance curve.

 

[EdStainless]

How different is the efficiency?
Will the savings on the pump be consumed in power within a year or two?
And more efficient pumps tend to be more reliable.

 

[desann]

Too many curves and legends. It will be helpful to show only a) Single pump characteristics b) combined pump characteristics. c) system resistance curve.

Here is a simplicited graph. The system curve is now for the system pressurized to 3,5 bar. So there's dead band of +-0,5 bar.

 

[desann]

How different is the efficiency?
Will the savings on the pump be consumed in power within a year or two?
And more efficient pumps tend to be more reliable.

Interesting and very important point! I have to look at that as well.

Other than that, in terms of performance and behaviour, do you see any pros and cons of either system?

 

[goutam_freelance]

There will be a pressure tank and high flow filter unit in the system.

How do you pressurize the system? Do you have any overhead tank to create a static head? A flow diagram will be useful.

 

[LittleInch]

Advantage of a steep curve is that the flow range between your system curves is relatively low so if you have a fairly fixed flow then this would only need a small amount of control, be it VFD or control valve.

A flatter curve gives you a wider flow range but would make precise flow control using a VFD more difficult.

All depends on what flow range you want to see.

 

[Artisi]

is anyone else as confused with the data supplied.

1. is the X axis in M3/H?
2. what does the Y axis represent?
3. what is Leo?
4. what is Pumpa blv?

following on to what goutam_freelance has suggested, besides a flow diagram, a sketch and detail of what's what might help a little.

 

[LittleInch]

is anyone else as confused with the data supplied.

1. is the X axis in M3/H?
2. what does the Y axis represent?
3. what is Leo?
4. what is Pumpa blv?

following on to what goutam_freelance has suggested, besides a flow diagram, a sketch and detail of what's what might help a little.

Keep up!

X is m3/hr, y is metres head

Leo is a type of pump with low head as is the pumpa blv

The OP is then running a second pump in series and his flow range requirement is between 8 and 12 m3/ hr with a variable fixed pressure requirement between 3.5 and 4.5 bar pressure at the end point of the system.

I've forgotten why he or she doesn't just get one pump to do the duty range but hey, that's what we're given.

Flow control by VFD of the higher head pump.

 

[goutam_freelance]

The OP is then running a second pump in series

The point is that how he can get a constant head at 0 flow unless there is a overhead tank to provide a constant head at all flows.
If you have two pumps in series without any static head then system resistance curve should have 0 head at 0 flow.

 

[desann]

is anyone else as confused with the data supplied.

1. is the X axis in M3/H?
2. what does the Y axis represent?
3. what is Leo?
4. what is Pumpa blv?

following on to what goutam_freelance has suggested, besides a flow diagram, a sketch and detail of what's what might help a little.

1. yes
2. head in m
3. first pump submerged in the tank for Ebara Matrix alternative
4. also first pump in series with Ebara 3M alternative

How do you pressurize the system? Do you have any overhead tank to create a static head? A flow diagram will be useful.

The pressure will be created by restricted flow by the fogging system, which will always limit the flow to either 4 or 8 m3/hr depending on whether both or single pumps are operating.