Pump design 4

[Ndimo]

On a slurry line I have a pump with the following design data :
Design @ duty : 10 000 gpm
BEP : 20 000 gpm
Actual flow max : 8 500 gpm
I'm experiencing frequent failures ( 150 mm shaft breakage)
My questions are :
- Should I blame the designer?
- Could I say that the failures result of a bad design?
- What should I do to return this pump near the BEP?

 

[sprintcar]

another thought - is it possible that at some point during one of the outages that the pump was started in reverse? This could have backed the impeller off until it hit against the suction plate, and possibly initiated some cracking damage to the shaft.

Since you are using pirate shafts, perhaps the shop rebuilding the bearing units is not following the OEM procedures or tolerances for the housing and bearings.

Keep the wheels on the ground
Bob

 

[sprintcar]

Hey guys.. did we scare him off or something???

Keep the wheels on the ground
Bob

 

[Artisi]

My thoughts exactly - seems a shame after all the input.

Naresuan University
Phitsanulok
Thailand

 

[Ndimo]

Hey guy,
I'm sorry for this long silence, I had too many thing to do that put this shaft failure in second importance. Nevertheless, our mechanical engineer has send the shaft to a specialised company for analyses and after many exchangers with GIW, it seems to us that they do not understand why we have those pump at that service, they are really poorly desgned. So, they are going to design new pumps wich mach the process as we can not change this later.
Thank to all for your inputs, I' not abble to say that is the real cause of the failures ( pump design, pump assemby, part ...) but we will move forward from now.

 

[sprintcar]

I think you might want to rephrase that 'poorly designed' comment.... as YOU stated:

boubacar (Chemical) 11 Feb 05 15:48
We are using those parts since 2001. Furthermore we have 4 pumps using them, but we have faillure only on one of them ( 2 shafts broken in 3 weeks). This later has commun suction and cummun discharge with another one, which experienced no problem.
How can I blame the part?

It appears 3 pumps are running fine. Perhaps your System, not the pump, is the 'poorly designed' culprit.

Any pump (or other equipment) is selected based on customer supplied parameters (head, flow, npsha, etc.) which may change over time due to production requirements, etc. It's incumbent on the the system manager or process engineer (like You) to understand both the original criteria and the current conditions so that either the pumps or the system can be updated to accomodate the new values.

I think just blaming GIW for this seems a bit short-sighted on your part. I looked at their website (

http://www.giwindustries.com

) and they've been doing this for over 100 years. Perhaps when this pump was originally installed, it met the system requirements. Or perhaps your previous systems engineer supplied the wrong information.

Remember, you're making these comments to an International Forum of folks who work in design and engineering...

As I stated earlier - Fix the PROBLEM, not the blame.

Keep us posted on how the issue is resolved, ok?


Keep the wheels on the ground
Bob

 

[Artisi]

I second strintcar comments - don't blame the pump - maybe you really mean to say that the system requirements that exist now are not compatable with the installed equipment.

Slurry pumps like GIW - don't break for no apparent reason.
Find the reason and make us all happy and you will also learn something.

Naresuan University
Phitsanulok
Thailand

 

[Ndimo]

Guys,
I second Artisi too, something is wrong. None wants me to talk about the pump althouhg the supplier itself agrees the pump is not convenable for this appication, good. But that I can tell you since that pump has designed, the process flow has increased by 20% we are still at 77% of design flow and at 42 % point of BEP ( desgin point was @ 55 % BEP). The NPSHa remains the same as at design.
As I wrote in my last post, we are going to design a new pump wich match the current process parameters.
Thanks again I will post you the final solution.

 

[PUMPDESIGNER]

I was just reading, learning a little, have been very busy so have not participated much.

Artisi is good theory of radial deflection.
That theory is even more likely if ...
You mentioned very low NPSHr, which of necessity drives the Nss high. If Nss reaches into the "high suction energy" zone, then any radial deflection occuring from Off-BEP operation may be dramatically exacerbated by the well known behavior of high suction energy pumps - THEY HATE TO RUN OFF-BEP, VERY STRONG REACTIONS AGAINST LOW FLOW RATES.

HI publishes a chart showing the high suction energy zone.
Scrounge around the HI site to find it, I don't know where it is, but that is where I got mine.



PUMPDESIGNER

 

[sprintcar]

Well - it's been 2 weeks - any resolution?


Racing and bullfighting are the only real sports...everything else is just a game.
Bob

 

[jotunbani]

greetings, I have a project in which I must evaluate the cost of a pump high pressure for salt water for one makes of desalination, the parameters that must satisfy the pump are a production of 1042 m3/h and pressure 70 bars.

thanks for your help

spanish version :

saludos , tengo un proyecto en el cual debo evaluar el coste de una bomba de alta pression de agua salada para una fabrica de desalacion, los parametros que debe satisfacer la bomba es una produccion de 1042 m3/h y una pression de 70 bars

gracias por vuestra ayuda

 

[Artisi]

Jotunbani
Saludos, you should start a new thread for this question, that way you will get answers from all the forum.

Naresuan University
Phitsanulok
Thailand

 

[Montemayor]

jotunbani:

Además de lo que te sugiere Artisi, toma en cuenta que no has indicado cual es tu problema o inquietud. Es decir, ¿que es lo que necesitas o requieres con respeto a esta bomba? Lo que nos has indicado es una descripción de tu proyecto. Supongo que eres capaz de llevar adelante la tarea que se te ha asignado.

Besides heeding Artisi's advice, you should state what your problem is regarding the pump. All you've said so far is what you have to do. I have to assume you're capable of doing what you've been assigned.

 

[jotunbani]

Hello I excuse myself for my former question which is not clear, I can't evaluate the price of a pump high pressure having the characteristics : Flow: 1042 m3/hr Press: 70 bars The graphs which I have are all according to H in meter (total head)

i need your help for to evaluate the cost of this pump

Thanks sirs for your help


Para MONTEMAYOR :

Saludos señor, me alegro que haya alguien aqui que sepa español,ya que soy un inutil en ingles asi que espero que usted me ayude en mi problema.

mi problema es el siguiente tengo que evaluar el coste de una bomba de agua salada que pueda satisfacer los parametros que ya dije arriba , los graficos que tengo solo me dan el coste en funccion de la altura manometrica y puesto que mi instalacion lo importante es la pression y el flujo, pues no llego a encontrar nada que me ayude en ello, espero recibir en breve su respuesta. o por lo menos que traduzca adecuadamente a los señores mi pregunta ya que como he dicho soy un patan en ingles


saludos jotunbani

 

[Montemayor]

jotunbani:

I reiterate Artisi's recommendation to start a NEW thread on your specific question. Multiple subjects or queries in one thread cannot be addressed efficiently nor accurately.

Nuevamente te recomiendo que presentes tu(s) pregunta(s) en un nuevo "thread". Es practicamente imposible el poder responder a varios temas en un mismo "thread" y esto causa confusion, resultando en un enredo.

 

[sprintcar]

I heard from a business contact that apparently this was simply due to insufficient NSPHA - the sump level was well below what the pump required and it ran in constant cavitation, with the failures becoming an issue when they switched to the 'pirate shafts'.

It was refreshing to see how all the engineering folks immediately 'defended' the original design. I guess we all understand that any product can be mis-applied beyond the designer's intent. This is a great 'family' to be a member of!

Hopefully boubacar has left with some education in system evaluation and problem resolution.

Racing and bullfighting are the only real sports...everything else is just a game.
Bob

 

[Ndimo]

Don't worry Sprintcar, I'm still here and my problem still pending. As you said, there is a low NPSHA and the pump doesn't suit the application. But, as it is more than likely that we cannot change the process to fit the pump, we are still looking for a pump wich can do the duty in good conditions.
Do you pratice Bullfighting when racing ?

 

[sprintcar]

Sure do - except I've got 23 other "Bulls" to deal with instead of just one....all of them 1300 lbs and 700 horsepower at 130mph on a dirt track....


Glad you're still here - let us know how you finally solve this!

Racing and bullfighting are the only real sports...everything else is just a game.
Bob

 

[rmw]

boubacar,

Check out

http://www.naglepumps.com

They make pumps for pumping slurries as well as fluids with solids, like coal boiler bottom ash, and steel mill scale to name a couple. I think I remember that they have the capabilities up to 14" dia. solids. Now that is an entrained particle.

Because of this, some of their models that I have seen in the field have some pretty hefty shaft diameters.

Their designs have generous clearances so as to allow lots of recycle. They are favored for people who have to pump explosives like TNT and DNT.

They may have the pump you are looking for.

But, they do use threaded impellers, so bump checking the motor in the wrong direction with the pump coupled can cause impeller to suction plate and/or shaft damage described earlier in this thread.

rmw

 

[Artisi]

rmw----- What you are describing is no different than what is available from many of the major slurry pump manufacturers.

Naresuan University
Phitsanulok
Thailand