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Increasing pump life; Reducing Wear
3

Increasing pump life; Reducing Wear

Increasing pump life; Reducing Wear

(OP)
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

RE: Increasing pump life; Reducing Wear

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: Operating region for pumps according to API

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.

http://virtualpipeline.spaces.msn.com

RE: Increasing pump life; Reducing Wear

(OP)
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

RE: Increasing pump life; Reducing Wear

Sorry, know nothing about slurries, but be patient, somebody else will give some clues about your remaining questions.

The only thing I can do is say, you can never overemphisize the importance of running at BEP, so that'll be a good start.

http://virtualpipeline.spaces.msn.com

RE: Increasing pump life; Reducing Wear

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.

RE: Increasing pump life; Reducing Wear

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.

RE: Increasing pump life; Reducing Wear

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.

RE: Increasing pump life; Reducing Wear

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!

RE: Increasing pump life; Reducing Wear

(OP)
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

RE: Increasing pump life; Reducing Wear

(OP)
***Also, TenPenny: Could you explain in further detail recirculation?
Thanks

Kapo

RE: Increasing pump life; Reducing Wear

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.

RE: Increasing pump life; Reducing Wear

(OP)
I have pictures.... can I attach them to the thread?

RE: Increasing pump life; Reducing Wear

(OP)
Pics: http://kapo84.myphotoalbum.com

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!

RE: Increasing pump life; Reducing Wear

You need to look at your controls and make sure that you are as close to BEP as possible at all times (spd vs flow).  Internal recirc will destroy you.

You also need to look at piping.  Excess turbulence or restriction will hurt also.

= = = = = = = = = = = = = = = = = = = =
Rust never sleeps
Neither should your protection
http://www.trent-tube.com/contact/Tech_Assist.cfm

RE: Increasing pump life; Reducing Wear

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.

RE: Increasing pump life; Reducing Wear

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.

RE: Increasing pump life; Reducing Wear

There is no need to shout - typing in lower case is sufficient for most people here.

RE: Increasing pump life; Reducing Wear

Sorry it is just out of habit that I type in caps. No shouting intended

RE: Increasing pump life; Reducing Wear

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.

RE: Increasing pump life; Reducing Wear

(OP)
Thanks again for all of your posts. We are currently making a few minor adjustments to our setup. We have installed a magnet on our Ball mill which should decrease the amount of damaging debris we have flowing through the system. We have also installed metal liners on our pumps that handle the larger particles. Other ideas we are considering range from changing to a larger impeller (16 inch instead of a 14.4 in), or going to a reduced eye impeller (to help decrease recirculation on our pumps that have lower flow), and/or changing the piping in our system.
We have a the pump reps out here lately and they are plugging numbers into their programs to try and help out. We'll see what they come up with.

I have posted a few more pictures of the most recent pump failure. It ran 684 hours (which is a little better than its average). It pumps the smaller sized particles @ ~850 GPM which is closer to its BEP than the other pumps we have. If you have a chance can anyone tell me what they think about the wear marks? It looks like recirc damage and a bit of cavitation. The mechanic decided to change out the liners when he saw slurry pouring out through those holes in the throatbushing. Also by the volute there seems to be a lot of wear, almost like the slurry is missing the exit point by a few inches. The impeller seems to have fairly normal wear.

Link: http://kapo84.myphotoalbum.com/

Thanks again for all of your comments.

~Kapo

RE: Increasing pump life; Reducing Wear

The impeller diameter change looks to be a wise move- it will reduce the pump speed a little which in turn should reduces the wear rate. It will beinteresting to see what comes from the change to metal liners - are you going to use hi-chrome iron?  

RE: Increasing pump life; Reducing Wear

(OP)
We are currently using Hi-Chrome Iron. Now as far as a larger impeller is concerned, will I simply just be increasing the pressure in side the casing? We obviously hope to decrease wear by slowing down the pump seed but one of my mechanics suggested that by going to a larger impeller we will significantly increase the pressure in the housing. Is it a choice of simply picking your poison?

Thanks Again

~Kapo

RE: Increasing pump life; Reducing Wear

(OP)
I believe we are using the Hi-Chrome Iron. Do you suppose by increasing impeller diameter will not only slow the pump down but increase pressure inside the casing thus increasing wear on the liners? Is a matter of picking your poison? Also, has anyone had experience with GIW(Georgia Iron Works) pumps?

Thanks again

~Kapo

RE: Increasing pump life; Reducing Wear

(OP)
Sorry for the duplicate...

RE: Increasing pump life; Reducing Wear

If you fit a larger diameter impeller and you wish to maintain the same flow and discharge head - you will need to reduce the pump speed.

For impeller diameter increase

flow will increase at the ratio of the diameter change
head will increase at the ration of the diameter change (squared) and power at the cube of the diameter change

For speed reduction
flow will decrease at the ration of the speed change, head at the square of the speed change and power at the cube of the change.

So it follows, increase the diameter and reduce the speed to give the pump duty which in turn reduces the wear rate rate

RE: Increasing pump life; Reducing Wear

I have to agree with Artsi and Pumpguykc in dealing with slurries speed is the key to wear rates, reduce the speed and life will go up. Generally this means pumps need to be sized 1 - 2 frame sizes larger, leads to increased project/capital/initial installation cost. Due to this the initial installation will be a smaller sized pump running at a higher speed. As polymet slurries can be very different depending upon the location, rule of thumb is used for the initial size. Actual running then provides the real situation. Feed this information back to the design and project team when the correct specific velocities for the slurry have been found.
What is the wear life in your pipelines like?
Regards

Mark Hutton


RE: Increasing pump life; Reducing Wear

(OP)
Thanks again for the responses.

I am thinking on paper here.... We have the pumps running off of VFDs. The VFDs are controlled by the mill box levels and the desired flow rate of the system. By increasing the impeller diameter we will be able to pump the same amount of slurry at a lower speed, thus reducing wear on our pump. This should especially be beneficial for those pumps that handle a large particulate.

We haven't had problems with wear on our pipelines. We are using a goodall hose because of how well it handles abrasion.   

RE: Increasing pump life; Reducing Wear

(OP)
Just as a little FYI; Our steel liners gave us 866 hours of life. A little over double our average at a little under double the cost. Not exactly what we were hoping for. I have been in contact with a pump manufacture and the larger impeller(25") seems to be the next step.

RE: Increasing pump life; Reducing Wear

(OP)
One other question:
    I am trying to determine which pump would run better in our system. The first is a 4X6 which has a peak BEP @ 70%. Due to our low flow we would only be able to run the pump at around 45%. The advantage to this pump is it is the same model as others we have so therefore we wouldn't have to worry about stocking unique parts just for this pump.
     Option #2 is a smaller 3X2 (21" impeller) pump which has a peak BEP @ 45%. We would run it in the 35-38% range.
Which is better?  
      I know it is always best to run a pump as close as possible to its BEP but will it more advantageous for us to stick with a more uniform pump setup?

Thanks again.
 

RE: Increasing pump life; Reducing Wear

What are the relative operating speeds of the 2 units.
There is a lot to be said for standardisation.
The 6/4 is more efficient at 45% than the 3x2 which is 35/38%.
In the end it comes down to an engineering decision based on your maintenace philosophy and the running costs.

RE: Increasing pump life; Reducing Wear

Very interesting answers you got here, the bushings that you currently use are they carbide and if so what kind, also high chrome ( Ni-Hard ) cast irons are only as good as the foundry producing them - w. other words the size of the microstructure components - if it is oversized ( poor foundry practice ) the wear resistance is also low...I would suggest using dissimilar materials for the impeller/diffuser assembly if any and/or casing if you are using open face impellers...Hard facing is an option of course however is a costly option, I do agree w. one of the responders that rubberized coatings will probably fail in this environment - I would suggest focusing towards picking up a proper alloy for the cast components instead, maybe one with VA heat treating capabilities  - another important factor is the corrossion component of the slurry, what exactly is the corrossive agent and in what concentration !!??

RE: Increasing pump life; Reducing Wear

(OP)
In order to determine what effect this impeller diameter change(and motor change) will have on our electricity costs per year I have done the following calculations:
(Do these numbers look right according to the affinity laws?)
New Impeller Diameter: 25"
Old Impeller Diameter: 14.4"
New Motor HP,KW: 75,(56.25)=60(?)
Old Motor HP,KW: 100, 75
Old Motor RPM: 1125
New Motor RPM:(75*1125/100)=487.7
Old VFD Kw draw: 57-60 kw/h

Impeller Ratio= 25/14.4= 1.736
New Flow= 937 gpm*1.736= 1626.6 gpm

Since we want to maintain the same flow as we do now we can multiply results by .576 as a correction factor. (1626.6*.576=937 gpm)

So, in order to get the new Kw/h value we...
    (57-60 kw/h)*(.576^3,correction factor)= 10.89 kw/h.

By increasing impeller diameter and decreasing motor size (as recommended by manufacture) we will save 30-50 kw/h.

Can you verify this?

Thanks again!!

Kapo

PS: these are the formulas I used:  http://www.mcnallyinstitute.com/02-html/2-01.html




RE: Increasing pump life; Reducing Wear

kapo84
Can you post a copy of the pump curve at the link you used previously (http://kapo84.myphotoalbum.com/) and advise exactly what the pump duty needs to be and the existing and suggested impeller diameters. We can then calculate the new pump speed etc. for you.

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