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Eductor to Progressive Cavity versus Diaphram Pump

Eductor to Progressive Cavity versus Diaphram Pump

Eductor to Progressive Cavity versus Diaphram Pump

(OP)
We are cleaning aquaculture pond waste using a high-pressure eductor pump and a venturi. This creates a
nice suction to pull the sediment up from the ponds,
which are 5' deep, 100' long and 20' wide. The shear,
unfortunately, takes an easily-settleable sediment
and turns it into a chocolate milkshake consistency.

Our consultant recommended diaphram pumps, however,
the horsepower and volume of air requirement is not
feasible, there's no plant air on the project sites,
and generally only single-phase power. Progressive
cavity sounds potential, provided it can dry-pump up
from the ponds up through the hand-cleaning wands and
into the above-ground suction-piping, hanging from
pond access walkways. I suppose a small driving-water
pump could supply priming to the progressive cavity.

I think I've answered my own question, but if someone
has other insight or experience, pond cleaning occurs
about once a week, running net 50gpm for ~8 hours, or
maximum 25,000 gallons of a miscible slurry, running
1,000 mg/L to 10,000 mg/L TSS.

The ponds may accumulate sands and pea gravels, however,
which is where we chose to borrow eductor-venturi pump
concept from hydraulic mining technology. The current
eductor works great, low maintenance, low cost, but new
discharge regulations are killing us on the 'milkshake'.
It will cost >$500K for sediment floc and filtration, so
the hunt is on for a robust, low-shear pump alternative.
If sands and pea gravels present an impediment, we can
always build a passive hydrocyclone on the ponds inlet.

Recap: 50gpm, miscible sediment @ 1,000mg/l to 10,000mg/l.
Low-shear pump, self-priming to 10', outlet pressure 30psi.

RE: Eductor to Progressive Cavity versus Diaphram Pump

I think you're going to get too much shear with a progressing cavity pump.  Maybe a portable air compressor and a diaphragm pump?  

There is also something called a Peristaltic Pump (do a google search, there's hundreds of them) that may also fit your needs.  One site ( http://www.watson-marlow.com/ ) claims to be able to move 350 gpm at 230 psig discharge.

David Simpson, PE
MuleShoe Engineering
www.muleshoe-eng.com
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

The harder I work, the luckier I seem

RE: Eductor to Progressive Cavity versus Diaphram Pump

As far as i know PC pumps are low shear? - i do however belive that they are not self priming? They are also sensitive to dry running.

While Perry only comments that they are "gentle to large particles" this short article also states that PC pumps are low shear:

http://www.pump-zone.com/articles/june04-10-11.pdf

(allthough a bit vauge in comparison to what?)

Try contact SEEPEX. They are one of the three (i beliver there are) main supliers of PC pumps.

http://www.seepex.com/cps/rde/xchg/en/hs.xsl/index.html

I have good experience dealing with this company.

Best regards

Morten

RE: Eductor to Progressive Cavity versus Diaphram Pump

Penn Valley makes a motor or engine driven diaphram pump.  Wanner engineering makes peristaltic pump. Peristaltic (hose pumps) are high maintenance. The hose always needs replacing or so it seems.

Regards checman

RE: Eductor to Progressive Cavity versus Diaphram Pump

This sounds like a natural application for an Archimedes screw pump.

Mike Halloran
Pembroke Pines, FL, USA

RE: Eductor to Progressive Cavity versus Diaphram Pump

If th head is low Mike got a point!

Best regards

Morten

RE: Eductor to Progressive Cavity versus Diaphram Pump

I'm not an expert in this kind of application, therefore please take my ideea with care :) -> I am thinking a 'swimming pool cleaner' system - like a baracuda cleaner ? - there is a model which looks like a lawn mower - the only thing you need to do is to have few of these units going linear next to each other from one end to the other when the cleaning is due....too simple to be true ?

RE: Eductor to Progressive Cavity versus Diaphram Pump

The pool cleaner is probably not far removed from what he's already got, i.e., eductor and attendant high shear.  The self- propelled versions could effect some labor savings, but the effluent would still be pretty well stirred up.

;--

An oversized Archimedes screw, operating at low rotational speed, should be able to lift the sediment as gently as anything could.  I guess it would have to be ~60 ft tall to meet the 30 psi head requirement.  With the length of screw and number of flights that implies, the sediment may come out too dry to flow in anything but a steeply pitched chute.

;---

Another thought on the diaphragm pump recommended by the original consultant:  He was probably not thinking of the compact pneumatically driven two- chamber version that is clearly in the minds of facs and zdas.

He was probably thinking of the single chamber pump with a diaphragm a couple of feet in diameter, driven by a connecting rod and an eccentric on a high-ratio gearbox, most commonly driven by a gasoline engine, sold for dewatering ponds.

;---

I don't understand where the 30 psi requirement comes from.  If there is some pressurized process downstream, I can understand it.  If it's just associated with transport to a further settling operation, then bigger pipes or open sluices with a gentle slope would make sense.

I.e., if the required lift was only five or ten feet, you could use an oversize eductor or other low head high volume pump with a relatively gentle flow.


 

Mike Halloran
Pembroke Pines, FL, USA

RE: Eductor to Progressive Cavity versus Diaphram Pump

(OP)
Thanks for all the ideas. The (multiple) ponds are in clusters around the site, and very low tech operation.
One person moves from pond to pond with a cleaning wand
plugged into a gallery of suction piping to the eductor.
Currently we gravity flow to sediment settling ponds, but
because of the "milkshake" eductoring, they get enormous.
Now with new Ecology reg's on TAN, BOD and P, we have to
remove the sediment from out of contact with decant asap.
We are considering everything from Geotube filtration
to ActiFlo floc-and-filtration to DAF, all of which
require some discharge head on the vacuuming system.
The diaphram and progressive cavity pumps offer this.
The archimedes screw doesn't, although I like the idea
that the sediment might dewater while it's being lifted.
From your ideas, now have lots of vendors calling. Thx.

RE: Eductor to Progressive Cavity versus Diaphram Pump

The 'gallery of suction piping to the eductor' implies that the shared eductor is running at a high lift, with high motive pressure and high throat velocity.

I'm thinking a low-lift eductor on the business end of the cleaning wand, with just enough motive pressure to get the sediment up and over the side of the pond, might reduce your milkshake problem.

Mike Halloran
Pembroke Pines, FL, USA

RE: Eductor to Progressive Cavity versus Diaphram Pump

I am not a lover of air activated diaphram pumps but feel that for your application they might be the best solution. I would couple this approach with a full review of the sludge dewatering and investigate using a filter press -  not a cheap unit to buy but overtime it might be easier and less costly than flocs etc and gives you a very dry and manageable end product - it will also use a lot less real estate.   

Naresuan University
Phitsanulok
Thailand

RE: Eductor to Progressive Cavity versus Diaphram Pump

(OP)
The eductor drive-water hose is an idea, but if you look at the hydraulics of eductors, shear is their middle name. Our dewatering plan keeps the solids as undisturbed as possible.
We are studying a cheaper solution to a filter press, see at Geotubes.com, basically geotextile dewatering bladders.
Too soon to tell if the permitting agencies'll approve it,
but they are being used for CAFO and CAAFO operations now.
On a side note, a colleague reports his facility devised a waste solids flushing system, that drains into a inclined plate settler, dual cell, that augers into a sludge pump, into a septage holding tank. Settler supernatant is pumped to a circular clarifier. But they have **lots of money**!

RE: Eductor to Progressive Cavity versus Diaphram Pump

I have seen settling trays with spooled textile bottoms, used for removing grinding swarf from water/oil machining coolant.  Think of a long linear settling tank with a slow- moving fabric bottom.  Clean fabric goes in one end, dry sludge comes out atop the fabric on the other end.

Mike Halloran
Pembroke Pines, FL, USA

RE: Eductor to Progressive Cavity versus Diaphram Pump

(OP)
Here's our tentative setup for 250gpm pond waste:

http://www.liftup.no  (air lift pond waste handling)
http://www.geotubes.com (geotextile filter bladders)
http://www.aquamizer.com  (seepage treatment to TMDL's)

Any seepage is at a lower rate than the pumping influent.
Budget of $50,000 should cover the capital improvements,
as opposed to $500,000 for a simple floc and sand filter.
CAFO and CAAFO are a growing concern for waste management.

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