Sump Pump Selection

[ER_Azza]

Hi All

Need a a bit of help. Not my speciality in pump.

Has an old sump pump, pumping water on a 2" pipe to a header - check valve before entry to the 8" header (about 5 meter high). Pump is running at 1460rpm. Pump head is 20m.

Looking to buy a spare and the only one proposed/available by the vendor is one driving at 2930rpm with a pump head of 40m.

SAME flowrate.

What's your thought?

 

[LittleInch]

Your new pump will probably go to the end of the curve so my guess is that you will get about 1.5 times the flow but your pump won't like it and could fail prematurely or make a lot of noise. Also your sump would empty faster so your pump might cycle more.

All this assumes that your current system actually pumps at your set flow rate. Does it?

You need to test it to find out.

More flow than its "rated flow" means your existing pump is already at end end of curve. Less means your new pump might be OK.

The stated flow is just a point on the pump curve where the efficiency is best but actual flow depends on the head lift and friction of the flow in the pipe and can vary widely.

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

 

[mk3223]

IMO, it’s good to have the spare pump the same size as the primary to have the operation flexibility. It can be operated as a 100% spare or run both pumps simultaneously and double the flow rate.

If with a larger spare pump, one option is to add a control valve at the new pump discharge and operate it to the flow same as the existing pump.

 

[LittleInch]

Unless most of the head loss is vertical lift, running both pumps together will not double your flow rate. You'll be lucky to see 25% extra. Friction losses in the same size pipe are proportional to flowrate squared.

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

 

[ER_Azza]

Hi ALL

Thanks for the feedback.
The sump pumps pump to a collecting pipe which send the water to the open catchment pond.
There is check valve just before entering the collecting pipe.

These are old pumps.
The current pump has a head of 20m (rotating at 1460 rpm, while the new one is 50m rotating at about 2930 rpm. My concern if the new pump will over-pressure the line - ;potential leak.

 

[pierreick]

Hi,
Unclear to me, why can't you purchase a pump from the existing supplier with the same characteristics (flow rate, head)?
Pierre

 

[ER_Azza]

Unfortunately the original pump is very old and they don't make them anymore.
Only limited supplier(s). So this the option given.

 

[mk3223]

You may verify the pressure rating and condition of the existing line and header if they are suitable for new pump of 50m head pressure.
We couldn’t figure it out by only wording….

 

[pierreick]

hi,
Then write specification sheet and send it to other vendors.
What is the name of your current vendor (pump manufacturer). Can you share with us the pump curve?
Pierre

 

[ER_Azza]

I am attaching the Proposed pump curve. Can't find pump the current pump curve. Attached also is the current pump data against the proposed.

FYI, it is just a sump pump. Being it is not my speciality, just want to get the best option.

 

[pierreick]

Hi,
Thanks for sharing!
You may want to consult other vendor:

https://www.xylem.com/en-us/brands/...&page=1&isbrandproductsearch=true&pagesize=24

KSB ,Moret
Pierre

 

[LittleInch]

What did you ask for?

If you asked for 20m head at 20m3/hr why did they give you one which did 50m??

Just ask for a pump with an impellor size of 127mm if you want to match your existing pumps.

The pump is unlikely to damage the pipe but will go off the end of the curve and damage itself or overheat.

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

 

[pierreick]

Hi LI,
Does not make sense to offer a pump with 50 m head and then ask to trim the impeller.
Pierre

 

[LittleInch]

Pierre, I agree, but we don't know what the pump supplier was asked to supply....

My point is that the same pump can be trimmed to supply 20m3/hr at 20m, the exact same as the OP has at the moment.

Maybe the supplier just pulled the last data sheet he had used and used that? Who knows?

It's clear the pump is a bit too big for the OPs use as 20m3/hr is a fair bit to the left of BEP, but not excessively so.

So my advice is that if the OP is happy with 20m3 at 20m head then go back to the supplier and ask him to revise his offer to use a 130mm impellor. It might then only need a smaller motor so might be a bit cheaper.

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

 

[TenPenny]

I would ask the vendor to look at the 1x2-11. I think it would be a good fit, and for sump pumps like this, 4 pole speeds are generally better.

I don't think I have access to the PSS Goulds sizing program any more, or I would do some curves.

 

[Artisi]

Change vendor.

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.)

 

[ER_Azza]

Hi All

Thanks for all the great feedback.
It was the site team that provided me with the vendor quote.
They could not find the spec of the current pump.

Recently, I found the original pump data sheet.
Agree with what were written by everyone.
I've gone back to the supplier to request for a closer match.

Just for discussion, I thought I presented the difference. I do admit I am no guru in rotating equipment.
I am more a static equipment person.

 

[Artisi]

Amazing what can be accomplished with the right data
A quick check on the Goulds site appears to have a pump suitable to your needs.

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.)

 

[TenPenny]

In so many cases, the vendor is given the kW rating of the pump, and if lucky, the discharge pipe size, and nobody in the field can give any better data. That's why things like this happen.

 

[LittleInch]

Clearly some miscommunication hence my question - what exactly was the vendor given to choose his unit other than clearly 20m3/hr.

The motor size for the current pump is much bigger than the load so won't be stressed, but will have a much bigger start current than is necessary.

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