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Centrifugal Screw Pump - any opinions?

Centrifugal Screw Pump - any opinions?

Centrifugal Screw Pump - any opinions?

(OP)
After posting a topic regarding PD type pumps, it appears to be more of a headache than its worth.  We are now considering a centrifugal screw pump for the slugde pumping application (RAS/WAS).

It does not appear to be very common, but looks as if this is the right pump for the job.  How is the maintenance on these pumps and have you used any in your jobs?  Also, who are the best manufacutrers of this type?  I have only found two that have a name with this pump: Hayward Gordon and Wemco-Hidrostal

Thanks.

RE: Centrifugal Screw Pump - any opinions?

Hidrostall is the original, as the story goes it was developed in Peru to pump live fish, very gentle.

This pump does a good job on RAS/WAS applications, good maintenance record. Have seen up to 7% sludge with very little derate, the screw is the key to accelerating the solids.

The down side is the impeller cannot be trimmed, so you must pick the pump close to your design point and use V-belts to get the performance you need or use a VFD (I would recommend).  Also be aware that discharge pressure can go very high if you run it back to "dead head" (the screw part of the impeller does this).

RE: Centrifugal Screw Pump - any opinions?

(OP)
Good info about not being able to trim the impeller.  Since this is coming out of the clarifier, the sludge should only be 2-3% max.  Would you lean towards using the typical non-clog or this?  Problem is that our client does not have the 'real estate' for belt drivin and VFDs are out too.  I was going to try to design a series of two-2 speed pumps to give a range of 4 flows.  Is this harder to accomplish with the screw impeller?

Thanks.

RE: Centrifugal Screw Pump - any opinions?

Try a rubber diaphram PD pump.  One that comes to mind that I used for RAS/WAS is Penn Valley Pumps.  Since your client does not have the realestate for variable speed, this company makes mechanical speed control devices that are mounted directly on the pump.  They worked great for me in the past.

Good luck...

BobPE

RE: Centrifugal Screw Pump - any opinions?

wickedpete,
You didn't say how large the required pump(s) were but I have a possible option for you for ASD requirement.

Have used these magnetic motor couplings for a variety of pump and blower services. They are cheaper than VFD's and take up no space.

You can check out their web site for more info and a local contact.
http://www.magnadrive.com/index.shtml

RE: Centrifugal Screw Pump - any opinions?

(OP)
what has been your experience with the magnetic couplings?  How accurate is the turndown and what is the max turndown?  

Flow range is about 350-1000 gpm and the prelim hp sizes are about 7.5

RE: Centrifugal Screw Pump - any opinions?

The "Magnadrive" units are a compact version of the old eddy current drives which were very reliable devices.  They have a very nice feature of not being able to transmit a torsional shock load.

Output shaft speed is always less than input shaft speed, so when the driver is an induction motor (the most likely case), the load (pump) speed will always be less than it would be if it were directly coupled to the motor.  The implications of this and the applicable affinity laws should be properly evaluated in your considerations--reduced maximum flow rate in all cases, reduced head for centrifugal pumps, etc.

These drive also have a nice feature in that they to not present the potentially troublesome electrical "noise" and torsional vibration problems that can be encountered with most adjustable frequency drives.  These drives do deserve serious consideration for suitable applications.

The efficiency of these drives compares favorably with adjustable frequency drives when all of the costs and features are taken into consideration.

RE: Centrifugal Screw Pump - any opinions?

(OP)
Thanks for the input.  I also contacted a rep and got some info from him about this application.  The function of this is favorable, but the pumps we are using are in the 10hp range and he stated that the cost/benefit is not as good for lower hp motors.  He suggests using the coupling on pumps with motors having 20+hp.

I will consider this for future applications though.

RE: Centrifugal Screw Pump - any opinions?

CB2 you are right about Hidrostal history. Wickedpete, to be honest I work at Hidrostal - Peru . First you have not written what is the operation point, please be specific about all the pumping liquid characteristic. Now let me give some important characteristic about our pumps.

Hidrostal´s screw centrifugal impeller pumps are very efficient for handling of bulky solids, sludges, slurries, viscous liquids, delicate solids, crystals and shear-sensitive liquids


Hidrostal's screw centrifugal impeller pump is a unique solution to the problems of efficiently handling either very delicate materials or a broad range of thick and viscous liquids, often highly abrasive or corrosive in nature. The Hidrostal´s screw centrifugal impeller pump has a specially shaped single blade impeller wich combines the properties of a centrifugal pump with the advantages of a positive displacement. It has a centrifugal outlet that allows pumping with the minimum of agitation and shear, essential factors when product bruising, liquid emulsification or clogging are to be avoided.

The screw centrifugal impeller provides several key benefits:

 Large free passages for pumping liquid with solid objects and fibrous materials  
 Able to pump liquids and viscosity's above values normally possible with conventional centrifugal pumps
 Steep H/Q curves with closed valve twice best efficiency  point  
 Low NPSH characteristics
 Flat non-overloading power curves
 High hydraulic efficiencies

After all this let me say that what you need is this type of pump. Please let me know if you need more information,pdf, videos, if you want I can sent you by mail more about this pumps. I also can contact you with our Export Department.Thank you  

RE: Centrifugal Screw Pump - any opinions?

wickedpete, the additional info you have given helps to clarify the potential application.

The Hydrostal would be a good fit if the discharge pressure is not too low, you are on the small side of the Hydrostal range of pumps.  Regarding the v-belt drive arangement, consider mounting the motor above the pump, very compact arrangement and easy to get from the manufacturer.

An alternative pump would be a two port nonclog (ok for 3% solids max)from Fairbanks Morse (1st choice), Goulds, or KSB.  These pumps will not be as efficient as the Hydrostal as they are true centrifugal, but the impellers are trimable for a specific duty point.

General note, when pumping solids the minimum velocity (GPM)is critical to a given system.  Basic application consideration that is missed by many.  Minimum velocity is also a consideration in two and three port non clog pumps.  Impeller design and ability to handle solids is not equal among the various manufacturers.

I urge you to give the VFD consideration in this application.  RAS/WAS pumping is very standard country for VFDs, and at this HP range the potential problems and costs that many seem to be concerned about are very minimal.  The cost of Two speed motors, controls and two speed starters add up to more than a good VFD and inverter duty motor (2:1 or 4:1).

It's all about proper application.

RE: Centrifugal Screw Pump - any opinions?

Your right about the two manufacturers. Hidrostal and Hayward Gordon are both commonly used on RAS/WAS.  The overhead motor mount with V-belt drive is also common and with a 10 hp motor will use less room than a standard horizontal direct mounted arrangement.  If you require more control consider a "variable control v-belt arrangement" for speed adjustment without changing sheaves and belts.

RE: Centrifugal Screw Pump - any opinions?

Wicked Pete,
Flygt N-Pumps are very good up to 4-5% solids in sludge, and they are more efficient than a screw impeller.

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