Axial flow pumping station help

[MartinLe]

We are asked if an existing pumping station (using auger pumps) that needs to pump to a higher elevation in the futire can be retrofitted with axial flow pumps (alternative would be building a new pumping station)

Flow ~10m³/s, 4m head.
Likely configuration will be several pumps plus some redundancy.
The problem is that in the lower reservoir, we only have 1,5m of water level.
Now when I look at pump datasheets (KSB amacan series), NPSH is (depending on pump size) 1,5 - 10m. Sulzer gives 2,4m for a 1m³/s pump.
My conclusion is for now that retrofitting the existing pumping station with axial flow pumps is not advisable because it would mean many small pumps due to the NPSH constraints.

Can someone with experience in designing axial flow pumping station do a sanity check of this conclusion?
Can someone point me to real life examples of similar pumping station so I get a better feel for the look?

 

[Artisi]

Any good reason not to stay with screw pumps?
1.5m water in the sump gives you an NPSHa of around 34m depending on temp. altitude etc. the problem will be ensuring enough submergence to overcome vortexing and air entrainment.
Don't waste time looking at general published data from the major pump companies, use the telephone or Internet and give all relative tech data and ask for their recommendations.

NOTE: should read NPSHa of approx. 11.5m not 34feet.
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.)

 

[LittleInch]

Err, Artisi - have you got the units right? 1.5m submergence in my world gives you about 11.5m NPSHA mac, maybe as low as 9-10m depending on altitude, temperature and inlet losses. 34 ft??

Otherwise agree - come up with a data sheet with as many bits of data as you can supply and then find a technical rep from the vendors and send them a proper engineering query. Vortexing and drawing in air needs to be addressed with that kind of flow rate.

The internet allows you to
a) find out if they make similar sized units
b) find someone relatively local to talk to

Specifics though are best dealt with by direct communication.

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

 

[Artisi]

Woop's --- thinking feet, writing metric or was that thinking metric and writing feet.
I will add note to original post.

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.)