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Increasing pump life; Reducing Wear 3

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kapo84

kapo84

Mechanical
Jun 4, 2007
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I am an intern and currently trying to determine a way to decrease the number of rebuilds we have to perform on our pumps annually. I work at a polymetallic mine. I haven't had much experience with pumps before but have learned a lot since I've been here. I have done a lot of calculations on our pump system and have come to a wall. We pump a high density slurry through 4 Warman 6/4 DAH pumps. We get anywhere 100-500 hrs of use out of them before we have to replace the liners/throat bushing/impeller. There are a number of variables that affect the system (tons/hour, particle size, etc...) which can complicate things but I know there is away to fix the problem. We put a man on the moon right?
I'll start by asking what main factors contribute to pump wear? Do I simply look at the characteristics of the slurry coming in or do I focus on the manner in which the pumps are being operated?
Any feedback will be helpful

Thanks in advance
 
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Saturn 5 rockets were one time use and disposable. I assume you would prefer not to do the same with your pumps, although its kinda' close anyway.

Both.

Keep the operating point within the range shown on the chart you can see at this thread,
thread407-186675

Maybe you can vary the consistancy of your slurry % solid vs % carrier fluid. It may be worth doing some studies on pump life vs specific gravity, pipeline flow characteristics, or the obvious.. abrasiveness of the slurry. You probably suspect what the cause of the problem is there already.


 
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We are running ~40-55% efficiency. We need to obviously adjust either the flow or possibly look at a pump that better meets our needs. It appears too big. As far as the pump components are concerned: At what point do you use metal impellers over rubber impellers? Rubber liners vs. Metal Liners? How much does paricle size affect wear(74-180 microns)?

Thanks
 
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The rule of thumb is fine material use rubber - large material use hard metal - although there are now a couple of manufacturers supplying "thick" rubber liners for larger solids ie, mill discharge duties which is the toughest application you can find for a slurry pump, also in some cases hi-chrome iron impellers and liners are being used successfully on fine materials.

My advice is to talk to the slurry pump manufacturers - they have the experience to advise on the best selection for each duty.
 
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If you are only geting 100 - 500 hrs from the impellers and liners then something is amiss, contact Warman or their agent and discuss it.
 
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You will need to identify what the slurry is, are the solids sharp-edged, or smooth...from there, you can make a decision on whether to go hard metal or rubber; many rubber liners are available with ceramic inserts to increase life.

If you are too far away from BEP, the recirculation in the casing will cause increased wear and reduced life as well, so an oversized pump can have a markedly reduced service life.

In your case, asking what the main factors are that influence pump wear...operating speed is a biggie; the slower, the better; however, as mentioned above, you want to stay above something like 70% of BEP for your pump, in order to minimize recirculation.

Try to balance those items, and you should also contact the vendor to see if there is a better material selection.
 
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In this application it will be the abrasive nataure of the slurry that is causing you som many failures.
Most slurry pump are internally coated with a rubber compound to reduce this wear and I seem to remember the impellers need to be of an open kind with a hard facing applied.
As has been said, contact your pump suppliers. That's what they are there for!
 
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Thank you for all of your responses. As far as the nature of the particles is concerned, they are sharp and the slurry contains a lot of quartz, which is hard on the liners.
We have been trying to solve this problem for years and the reps have been out to help us but no one has seemed to come to a common consensus on what the problem is. Some agree that it is as good as it will get.
We have the white-iron impellers with rubber liners in all of our pumps. We will be trying metal liners in one of the pumps here soon.... so we'll see what happens.
Does anyone here work in the mining industry? It would be interesting to find a similar mine and know how often their pumps last them.
Thanks Again guys...
Kapo
 
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a selection of photographs of the worm components would be helpful so that we can see the nature of the wear and further application information, what is the average solids size, percentage, pump speed, open or enclosed impeller, why are you changing to metal case liners - are the rubber liners being torn and for interest, where are you located.
 
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Pics:
We are running a 5 vane closed impeller. On the Sagmill our GPM runs anywhere from 168 GPM to 232 GPM. Our D50 is ~150-160 microns. Our pump speed I believe is around 850-900 RPM (I need to verify this). Con of solids %/vol is 52%. We are changing to a metal liner on our other pump which comes out of our ball mill. The D50 is around 75 microns and the GPM ranges from 300-500 GPM.

I really think we can keep the pumps we have it is just a matter of trying to tweak the variables in order to decrease the amount of recirculation and at times caviation.

By the way we do have VFD running our pumps.

We are located up here in Alaska.

Hey thanks again guys for all of your help!
 
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I think you need to define the operating point of the pump in terms of flow and discharge head in relation to BEP, what is the pump speed speed, are there any "foreign" solids gaining entry to the pump.
I would suggest that the 6x4DAH maybe oversized for a duty of round 200 USgpm and could be resulting in a lot of recirculation which leads to accelerated wear and shortened life, however this is also a function of speed.
The impeller looks to be fairly normal for this type of application and has plenty of life left in it, how many hours has it done and if it is a ni-hard (white iron)impeller I would change to high-chrome iron?
As for the liners you need to carefully analyse the number of hours and the actual pump duty pump compared to BEP and pump speed to establish if the pump is actually suited for the application. If the pump is suited in terms of speed and duty / BEP I would change to high-chrome liners as a start to retification of what looks to be unacceptable wear rates.

Are the pump representives qualified to assist you in this matter, it appears they are not. If this is the case I would be inclined to assemble all your data and photo's and consider emailing this information to Warman in Australia who have the experience to advise on this.

As stated in an earlier post- mill discharge is probably the toughest duty for a slurry pump, you have to pump extrememly sharp like size particals at varying consistencies and flow rates - this is extremely arduous and hard on pump wear components as has been demonstrated by your application.
 
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WE HAVE DESIGNED PUMP SYSTEMS IN SEVERAL ABRASIVE SLURRY APPLICATIONS AND THEY WORK BEAUTIFULLY. WE USE NI-HARD PUMPS, OVERSIZE THE PUMP AND RUN THEM VERY SLOW. OUR LIFE ON SLURRY PUMPS IS ANYWHERE FROM 2-8 YEARS. MANY TIMES RUBBER LINED PUMPS GET CHEWED UP DUE TO CAVITATION AND LARGE SOLIDS EATING AWAY AT THEM. WHAT IS YOUR DISCHARGE HEAD PRESSURE? THE OTHER THING TO DO IS USE A RECESSED DESIGN IMPELLER. THEY ARE NOT AS EFFIECIENT BUT IF YOU TRIPLE THE LIFE OR BETTER OF YOUR PUMP THERE IS A TRADE OFF.
 
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Have you consider progressive cavity pump ? It would be worth looking at this, this type of pump is design to pump 30-40% solids and it is for slurry application. Anyway I do not know how sharp and large are the solid, if it will cut through the stator.
 
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