Centrifugal Pump - Priming

[Brams1]

First post, so please go easy! I'd like to hear your thoughts on my mechanical design conundrum. The short story - can an end suction centrifugal pump volute be left underwater to maintain prime?

I'm looking to design a pump pontoon for pumping industrial wastewater, which may have some solids. Approx duty is 1000 GPM @ 115 psi (230 M3/hr @ 8 bar). The pump will intermittently operate, so maintaining prime is critical, however, I'd like the pump to be able to maintain prime without a footvalve. In my experience in similar applications, footvalves have been unreliable - the solids passing over the sealing surfaces wears them quickly until they develop slow leaks, which causes an eventual loss of prime.

To avoid the foot valve, I have considered and decided to avoid:

• vertical turbines (expensive + long lead time)
• submersible pumps (difficult to mount onto pontoon structure, difficult to service/access).
• Self priming centrifugal (low efficiency+expense)

Weir minerals builds the APNH pump pontoon with their end suction centrifugal Warman DWU pump, with the pump volute designed to remain half underwater (cyan line on diagram, see picture), which means the pump is automatically primed. Can most/all end section centrifugal pumps be left with the volute underwater to ensure constant prime?

It'd be great if it could - I see a direct driven centrifugal pump having ease of service/lead time/cost and availability advantages.

Thanks all!

 

[LittleInch]

What's wrong with vertical centrifugal pumps like this? https://www.sujalpumps.com/vertical-centrifugal-pump-a-brief-guide/

The issue I see is that the bearings are not designed for an angle and the seals also.

You either need a long drive shaft or this looks like it uses a chain drive to move the motor out of the water.

 

[Artisi]

Simply design the pontoon with a dry well below the water level, mount the pump vertically onto a flange, with or without an isolating valve between the pontoon flange and the pump to suit your needs.
The well only needs to be deep enough so the pump case is below water level.

Nothing new, no rocket science involved.

 

[Andrew ONeill]

I haven't seen a setup like this in practice, but I don't see it being any different to a vertical submersible pump, that is common in slurry process sumps where the entire volute is submerged for the same reason. I agree a foot valve is Maintenace nightmare in a slurry service and agree with the approach to avoid using one.

As a general concept Warman slurry pumps are built "like a brick sh*thouse" as the saying goes, so I wouldn't be too worried about wear, random vibrations, flex etc. At the end of the day, the pump shaft seal will be semi submerged, which I can't imagine is a problem, in fact is probably better than having it non submerged. Just a case of keeping the bearings in the bearing block un-contaminated, might be an issue with keeping bearings lubricated, but i'm sure there is a way to deal with it that gives acceptable performance.

I'm assuming by looking at it, that pump base is on a pivot, for maintenance reasons, so that's a nice touch. As a maintainer I'd much prefer working on a horizontal pump like this than one of the vertical options, which in practice all you can do is remove and send to a shop somewhere, whereas with your proposed arrangement it is possible to replace bearings, mechanical seals etc in the field if needed.

In your quest to avoid a foot valve, the only other option I've seen is an external priming system, basically an external vacuum pump on the piping system itself rather than being part of the pump assembly. This would allow the centrifugal pump to be setup more traditionally, but in reality probably is more problematic than the solutions suggested.

 

[Brams1]

What's wrong with vertical centrifugal pumps like this? https://www.sujalpumps.com/vertical-centrifugal-pump-a-brief-guide/

The issue I see is that the bearings are not designed for an angle and the seals also.

You either need a long drive shaft or this looks like it uses a chain drive to move the motor out of the water.

Hi LittleInch, Thanks for the response! I had considered it, but the vertical centrifugal pumps. typically deliver significantly less pressure than required for the application.

I hadn't considered the angle of the pump being an issue for the bearings/seals, but definitely something I need to be keeping in mind here! Cheers !

 

[Brams1]

Simply design the pontoon with a dry well below the water level, mount the pump vertically onto a flange, with or without an isolating valve between the pontoon flange and the pump to suit your needs.
The well only needs to be deep enough so the pump case is below water level.

Nothing new, no rocket science involved.

Thanks for the response Artisi! Incorporating a dry well could be a great solution - I'll have to figure out how to manage heat build up from the motor vs water tightness from rain above!

Regarding the pump mounting on a flange, as well as the isolating valve, I'm not entirely sure what you mean by that. Did you have any further details or examples of products you had in mind?

Thanks again!

 

[Brams1]

I haven't seen a setup like this in practice, but I don't see it being any different to a vertical submersible pump, that is common in slurry process sumps where the entire volute is submerged for the same reason. I agree a foot valve is Maintenace nightmare in a slurry service and agree with the approach to avoid using one.

As a general concept Warman slurry pumps are built "like a brick sh*thouse" as the saying goes, so I wouldn't be too worried about wear, random vibrations, flex etc. At the end of the day, the pump shaft seal will be semi submerged, which I can't imagine is a problem, in fact is probably better than having it non submerged. Just a case of keeping the bearings in the bearing block un-contaminated, might be an issue with keeping bearings lubricated, but i'm sure there is a way to deal with it that gives acceptable performance.

I'm assuming by looking at it, that pump base is on a pivot, for maintenance reasons, so that's a nice touch. As a maintainer I'd much prefer working on a horizontal pump like this than one of the vertical options, which in practice all you can do is remove and send to a shop somewhere, whereas with your proposed arrangement it is possible to replace bearings, mechanical seals etc in the field if needed.

In your quest to avoid a foot valve, the only other option I've seen is an external priming system, basically an external vacuum pump on the piping system itself rather than being part of the pump assembly. This would allow the centrifugal pump to be setup more traditionally, but in reality probably is more problematic than the solutions suggested.

Hi Andrew!

The Warman pumps (DWU model) appear to be a serious piece of kit. They don't look like they'd come cheap however, so they may not be my first choice pending quotes! I'm based in Australia so the Stalker SHD is on my radar, but happy to take recommendations if you have any.

Correct, the pump base is on a pivot for maintenance reasons, definitely a very nifty feature.

I'm trying to avoid an external priming but its definitely an option.

Thanks again!

 

[LittleInch]

Hi LittleInch, Thanks for the response! I had considered it, but the vertical centrifugal pumps. typically deliver significantly less pressure than required for the application.

I hadn't considered the angle of the pump being an issue for the bearings/seals, but definitely something I need to be keeping in mind here! Cheers !

You can't find one doing 8 bar??? Are you serious. Look harder.

 

[Brams1]

You can't find one doing 8 bar??? Are you serious. Look harder.

Hi LittleInch, I think my research has been fairly comprehensive - they typically top out at 35-40m of head. Just so we're on the same page, the Ruhrpumpen VSP is the style I have tried to find.
Cheers!

 

[Artisi]

Thanks for the response Artisi! Incorporating a dry well could be a great solution - I'll have to figure out how to manage heat build up from the motor vs water tightness from rain above!

Regarding the pump mounting on a flange, as well as the isolating valve, I'm not entirely sure what you mean by that. Did you have any further details or examples of products you had in mind?

Thanks again!

Can't see any problem with heat build up, why would there be? - I assume the unit would be mounted on a open pontoon, as for rain, put a roof over it.
You will need a stand-off flange on the pontoon bottom on which to mount the pump, the valve idea was to allow the pump to be removed at anytime without flooding the sump.
I supplied 12 units in thus configuration to an aid project in Laos 30 + years back for flood irrigation and saw 1 unit still in operation about 10 years back when I visited that area.
I've been away from, the industry for too many years so don't know what's available today.

Where in Aus are you?