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
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
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
Thanks
RE: Increasing pump life; Reducing Wear
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
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
RE: Increasing pump life; Reducing Wear
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
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
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
Thanks
Kapo
RE: Increasing pump life; Reducing Wear
RE: Increasing pump life; Reducing Wear
RE: Increasing pump life; Reducing Wear
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http://virtualpipeline.spaces.msn.com
RE: Increasing pump life; Reducing Wear
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 also need to look at piping. Excess turbulence or restriction will hurt also.
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RE: Increasing pump life; Reducing Wear
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
RE: Increasing pump life; Reducing Wear
RE: Increasing pump life; Reducing Wear
RE: Increasing pump life; Reducing Wear
RE: Increasing pump life; Reducing Wear
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
RE: Increasing pump life; Reducing Wear
Thanks Again
~Kapo
RE: Increasing pump life; Reducing Wear
Thanks again
~Kapo
RE: Increasing pump life; Reducing Wear
RE: Increasing pump life; Reducing Wear
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
What is the wear life in your pipelines like?
Regards
Mark Hutton
RE: Increasing pump life; Reducing Wear
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
RE: Increasing pump life; Reducing Wear
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
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
RE: Increasing pump life; Reducing Wear
(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
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.