Does anyone have experience with recessed impeller pumps?

[relentlessratt]

I am considering the use of a vertical cantilever recessed impeller pump for a sump application. The pump product has sand, silt, vegetation, BS&W and some amount of sticky oily sludge. what are your experiences with recessed impeller pumps? do you think this is a suitable application?

 

[Artisi]

Yes, good selection, although you still have to consider the size of the solids and the solids passing capabilities of the pump.
What is BS&W?

 

[relentlessratt]

BS&W=base sediment and water.
the largest solid size should not exceed 3/4 inches. I have looked at a few manufacturers flowserve, goulds but TOYO pumps seem to have the best designs when it comes to recessed impeller pumps.
what other manufacturers would you recommend?

my major concern is the sand. i feel that the impeller and casing may still wear.

 

[Artisi]

Of course the pump will wear, sand is abrasive however, how much sand is there?
What flow rates and head are you looking at?
What does the vegetation consist of?

You may need to go to hard metal preferably Hi-Chrome iron for the impeller and casing - check Warman for their cantilevered sump pump.

 

[relentlessratt]

Lets say about 10% sand by volume as worst case.
service A: 200 GPM @ 230 ft
service B: 800 GPM @ 120 ft

The vegetation is mostly grass and fallen leaves. These tend to adhere to suction strainers in the presence of oil so i'm thinking about a chopping device at the impeller inlet.

researching warman now, thanks.

 

[Artisi]

10% of sand by volume is a full-on slurry pump and you will probably need to run without any suction strainer - can see major problems with the vegetation and the oil.

I see other problems with the pump duties in regards to the flows and head especially service A - this will be a pump running well to the left on its curve (if you can find a small slurry pump with recessed impeller capable of this duty range), with such a turn-down you will probably get a lot of re-circulation within the pump resulting in accelerated wear of the pump.

You might have to re-think the application and the range of flow / head.

 

[relentlessratt]

i am thinking to spill back some of the fluid to the sump to maintain an operating point close to BEP for service A - the curves i've seen cannot provide the head and flows together for this service.
service A and B will be 2 separate pumps but in similar applications so turndown should not eb an issue - i should have explained that earlier.
still, i feel there aren't other designs that can work better than a recessed impeeller pump in this application.

 

[moltenmetal]

There are recessed impeller dredge pumps which might be able to handle a situation like this. The suction is literally inserted into beds of underwater sediments and it pumps them whole, including rocks up to about 3" diameter. It was many years ago when I heard of this thing and it was odd enough to remember it even now, but I have no experience using such a thing and I'm afraid that I don't have a vendor name to recommend.

I'm sure any pump you choose will wear, and lines or other parts of the system will still be subject to plugging by some wierd combination of solids of various sizes, stringy bits and glue (oil/grease).

 

[SteveWag]

Look into a Wemco Model “C”, I have seen them pump live fish, wire rope and lots n’ lots of sand and grit.
Steve

 

[relentlessratt]

thanks.

 

[relentlessratt]

Artisi/Moltenmetal/SteveWag,
Thanks for your input on this selection. I've decided to go with the recessed impeller design. I'll just have to spill some product back into the sump to maintain a good operating point. Thanks again.

 

[Artisi]

The only problem with re-circulating back into the sump is that sand component of the product gets pumped many times --each time you pass the sand thru the pump results in more wear.

 

[relentlessratt]

Artisi,
Many different designs were tried in these services in the past - diaphragm, piston, self priming centrifugal, vertical turbines. Back then, i was still in school but from the data i have, all these designs performed poorly with Mean time Between Repairs ranging from 3 months - 9 months. so the services were very maintenance intensive and costly too.
you have an excellent point about the re-pumping of sand. If i can get 3 - 5 years problem free operation with the recessed impeller design, I won't mind replacing worn components with this runtime. do you think this is a reasonable runtime for services of this kind or maybe too ambitious?

thanks.

 

[Artisi]

It comes down to:
1. can you get a pump that is comfortable in operating at duty A and duty B. I think the first thing you need to do is locate a pump that is capable of the hydraulic duties.
2. If you can find a pump - then you need to look at material of construction options available.

An all metal slurry pump in 28% chrome should give you reasonable life provided it is within the hydraulic capabilities.

Warmans used to manufacture a cantilevered slurry pump - you need to check what is now available.

 

[relentlessratt]

Artisi,
I checked out warman. their recessed impeller design cannot provide the head for the services. they do have a couple designs such as the double suction seal-less open impeller which looks interesting. i don't know if you or anyone has any experience with that design. my concern would be the vegetation as there is a tendency to plug open impellers. At least thats what used to happen to the self primers we had before. thanks for you input again.

 

[ccfowler]

If you have or can arrange for a reasonably clean water supply, you may want to consider a jet pump arrangement (probably multiple stage) for this duty. A jet pump system may use more energy, but by careful choice of materials and configuration, wear and plugging problems can be minimized or avoided.

Valuable advice from a professor many years ago: First, design for graceful failure. Everything we build will eventually fail, so we must strive to avoid injuries or secondary damage when that failure occurs. Only then can practicality and economics be properly considered.

 

[Artisi]

If you have long stringy type vegetation reducing the width of the impeller blade to give more clearance between the impeller and the casing is one remedy, some rework to the blade shape can also help. This reduces pump hydraulic efficiency but, if it works without clogging then pump efficiency becomes 100%.

ITT Goulds who incorporated the Allis Chalmers pump business have an impeller from AC pump range called the Shearpeller, this allows large air-handling capabilities and and capacity to pump long stringy product with reasonable efficiency - not sure if Gouldss have a cantilevered pump rangs and if this impeller can be fitted - assuming they have such a pump.

Although I have no direct experience - Nagle pump company will probably have something to suit.

 

[relentlessratt]

ccfowler,
i don't believe that we have the luxury of a readily available source of clean water. but, i will look into your suggestion and see if its practical.

Artisi,
the goulds designs i've looked at in their GPM catalog can't provide the head required for the applications. the shearpeller is a horizontal design i believe and won't be able to lift the product. i will send them a request for quotation. see if they have anything new that i haven't seen as yet.

thanks again to you both for your great advice.

 

[ccfowler]

relentlessratt,

You don't need to get crazy about the cleanliness of the water for a jet pump. It just needs to be clean enough to avoid erosion or plugging problems. Decent fine straining would probably be adequate. Sand bed filters would surely provide clean enough water--two in parallel would allow continuous operation with one in service while the other is in backwash mode. (You may want to look at swimming pool filters as a readily available source of sand bed filters in many sizes at modest cost.)

You may want to use a jet pump as a first stage to make the recessed impeller pump adequate for the rest of the lift that you need. I would seriously consider using just multiple stages of jet pumps because of the stringy material and erosion concerns. The balance of costs, reliabiity, and maintenance requirements could prove to be very interesting.

Because of the potential problems with stringy materials, you may want to use jet pumps configured for straight-through axial flow of the pumpage with the high-velocity jets arranged around the circumference and directed toward the venturi. Efficiency of this configuration suffers a bit, but the main concern is getting the nasty, hard-to-pump stuff to flow reliabilty.

If you can't find exactly what you need, jet pumps are simple enough that you can probably have what you need custom made.

Valuable advice from a professor many years ago: First, design for graceful failure. Everything we build will eventually fail, so we must strive to avoid injuries or secondary damage when that failure occurs. Only then can practicality and economics be properly considered.

 

[TenPenny]

I don't know if the Vaughn Chopper pump can handle the head you're looking for, but it's worth investigating, as for the service, it would have no issues.

The Goulds CV3171 (recessed impeller, vertical sump pump) can't do 230 ft head unless you run it at 2pole speeds, which might become a wear headache if you've got much grit in there.