pump allowable operating range
pump allowable operating range
(OP)
Dear Friends
As a mechanical engineer I have to approve vendor documents (VP) for centrifugal pumps, working in a petrochemical plant. Unfortunately some performance curves don't meet allowable operating region (70%-120%), determined by API-910. Some pumps have rated capacity in 40% of BEP capacity but the Vendor urge us to accept VP because according to his experience no problem is likely to happen.
Being under the pressure of my supervisor, shall I accept deviation from API-610 which governing out project?
Mohammad
As a mechanical engineer I have to approve vendor documents (VP) for centrifugal pumps, working in a petrochemical plant. Unfortunately some performance curves don't meet allowable operating region (70%-120%), determined by API-910. Some pumps have rated capacity in 40% of BEP capacity but the Vendor urge us to accept VP because according to his experience no problem is likely to happen.
Being under the pressure of my supervisor, shall I accept deviation from API-610 which governing out project?
Mohammad





RE: pump allowable operating range
In our plant, we require the selection to fall between 80 and 105 percent. If this cannot be met, we have to install a minimun flow spillback to allow us to control to that range.
Johnny Pellin
RE: pump allowable operating range
It all really depends if your duty is relatively fixed or can vary. However in this case I would tend to agree with JJPellin, that you should not accept this deviation. If this is repeated many times I would also add up the absorbed power required compared to what would apply if you had pumps all at the proper range, you might be surprised by how much extra power you would consume. Even if you generate all your power, it isn't free..
Definitely sounds to me like the vendor is trying to pull a fast one, but stick to the required specs unless there is a very good reason to deviate. This doesn't sound like one to me.
My motto: Learn something new every day
Also: There's usually a good reason why everyone does it that way
RE: pump allowable operating range
If I persist on performance curve rejection our vendor is likely to be totally rejected and this may cause considerable cost impact. As being a young engineer I fear to deviate project specs but my manager said don't consider higher energy consumption just tell us whether this pump operates technically good or not?
I'm completely agreed with JJpellin and LittleInch but I have made this post to see if anyone else have face such a condition and know about the operation and probable failure of a pump which operates out of the allowable operating region (70%-120%)?
Thank you in advance!
RE: pump allowable operating range
What is the service? what fluid are you pumping?
What "type" of pump is it? single stage overhung, between bearings?
Capacity is 40% of capacity @ BEP but what is the efficiency loss in % ?? (from what % down to what %)
There are occasions where selection criteria could be more important than %BEP, heavy solids app?, viscosity?, super low NPSH....all you are getting are guesses without you supplying some of this info to us.
Other than the obvious power waste, the other concerns running far left of BEP would be increased radial loads on the shaft which can wear out bearings, seals, increase vibration.......of course this is not near the concern on a btween bearing pump that it would be on an overhung. So to provide you better info to build your case, please give us some detail.
On a side note, you don't always get what you pay for when you buy expensive, but you always do when you buy cheap.
RE: pump allowable operating range
I will appreciate if you could check this thread again.
RE: pump allowable operating range
On this forum we can confirm your concerns but can't always solve your problems.
I agree with all things said by dubmac, but unless there are good technical reasons why they are operating in those ranges, then efficiency is the key issue. At the least you need to send a technical query to the vendor detailing the parts of 610 that he is not in compliance with and or sections of the data sheet and requesting a technical response. If you get overruled later on by your managers then at least you can point to this if the client complains later on.
My motto: Learn something new every day
Also: There's usually a good reason why everyone does it that way
RE: pump allowable operating range
RE: pump allowable operating range
http://files.engineering.com/getfile.aspx?folder=9...
Flow (m3/hr)
VIS [mPa·s]
Fluid CAUSTIC SOLUTION 5-10%
RE: pump allowable operating range
If the pump being offered is 40% of required total capacity, Then you're looking at buying two and operating both of them at 125% of their BEP flowrate to equal system capacity. But I'd be looking at buying two pumps, each with a capacity of 50%-60% of required system capacity (at BEP) and operating them at 80-100% of their BEP flowrates.
Example:
System flowrate is 300 m3/h. Look at buying two pumps.
Power needed at that flowrate is 500 kW from each pump motor.
Each pump with a BEP flowrate of 150 m3/h and with a maximum rated capacity & motor power sized for somewhere around 170-180 m3/h at 500 to 600 kW. That power level is actually around 15% - 20% over the 100% continuous duty rated power (at 150 m3/h) of 500 kW.
Then you can operate comfortably at a BEP of 150 m3/h while at a power setting of around 80% to 100% of rated power. 80% if the motors are 600 kW, 100% if the motors are 500 kW. Pick a standard motor size at or between 500 to 600 kW and let the % of rated power at continous duty fall where it may.
Independent events are seldomly independent.
RE: pump allowable operating range
In fact you may not be doing anything at all shortly thereafter.
Independent events are seldomly independent.
RE: pump allowable operating range
I would use a different example. The required rated flow for their process is 40 gpm. They went to their pump vendor and asked for a pump to satisfy this flow rating. The vendor came back with a pump that has a Best Efficiency Point flow of 100 gpm. If they purchased this pump, it would be running at 40% of BEP. The vendor indicates that their pump should run well at 40 gpm. I would not recommend purchasing a pump that is so severely oversized for the required service conditions.
Johnny Pellin
RE: pump allowable operating range
Gilus02 - with the relatively skimpy detail in your table it's difficult to be sure, but pump 103 appears to have only a small drop in efficiency for duty / BEP, but some of the others are dreadful efficiences and grossly over rated. As you haven't put head or power or any of the curves it is difficult to say much more....
My motto: Learn something new every day
Also: There's usually a good reason why everyone does it that way
RE: pump allowable operating range
RE: pump allowable operating range
Is your flow range min to max or min to rated?? It does make a huge difference and could be why you're getting the response from the vendors like this.
My motto: Learn something new every day
Also: There's usually a good reason why everyone does it that way
RE: pump allowable operating range
Dear friend; in this case we don't want two pumps working in parallel but you have indicated a point that I haven't already known. Thank you very much!
@JJPellin
Dear Johnny; You have provided a clear and meaningful example. I wouldn't recommend purchasing this pump too, but in a one special case (based on my personal knowledge) I think two soluion could be applicable, (please make me correct if you see anything wrong)
1- Impeller trim
we may asked vendor to study whether another size (larger or smaller) satisfy our condition better? Probably vendor have already done.
2- By Pass
Let the pump operating a flow near the BFP and draw a pipeline from discharge to suction to make the net discharge flow as minimum as we want. This solution requires higher power consumption but on the other hand it may reduce pump vibration, bearing wearing, temperature and probability of failure.
Mohammad
RE: pump allowable operating range
We have just determined normal flow and rated flow for the vendor and all the other data were proposed by vendor like max flow, min flow or flow at BEP.
Mohammad
RE: pump allowable operating range
Independent events are seldomly independent.
RE: pump allowable operating range
RE: pump allowable operating range
As you have rejected them your job is done until the vendor comes back to you, but the general consensus is that you have been correct to reject them as they seem grossly over sized which would lead to prmeature failure in the long run as well as increased power consumption.
My motto: Learn something new every day
Also: There's usually a good reason why everyone does it that way
RE: pump allowable operating range
So.... Just ask them for a lower specific speed selection and see what turns up?
RE: pump allowable operating range
BEP is defined as THE PUMP'S FLOW RATE AT THE POINT OF [b]BEST EFFICIENCY[/b].
Are you actually saying that your pump has a rated capacity of 40% of its own best efficiency point?
Why in the world would a pump have a rated capacity of 40% of BEP.
I CAN'T MAKE ANY SENSE OF THAT.
Who is this pump manufacturer and what model is it?
Independent events are seldomly independent.
RE: pump allowable operating range
So the pump only has "rated capacity of 40% of it's BEP" if they purchase that pump for that service.
RE: pump allowable operating range
I'm outta' here.
Independent events are seldomly independent.
RE: pump allowable operating range
But yes, the question was "would it ever be acceptable to purchase pumps to be operated at 40% of BEP" because he had management pressure to accept that (terrible) selection.
RE: pump allowable operating range
You are the professional . Say "no" to the boss. The boss is trying to bully you. All bullies are cowards. If you tell the boss you cannot recommend the pump but he is free to override you what can he do? The boss will either back down or get someone else to sign off. You might like to look for another job as you dont want to work for someone like that anyhow.
Engineers should stick by their professional ethics. Their duty is to the public interest and good first and the company they work for second. If you dont believe this then get out of the profession.
“The beautiful thing about learning is that no one can take it away from you.”
---B.B. King
http://waterhammer.hopout.com.au/
RE: pump allowable operating range
Being involved in Oil & Gas industry for just 3 years I couldn’t take this risk and approved the standard deviated pumps. My boss (not so bully!) said if you don’t accept these 4 pumps the vendor is likely to be rejected and he will make financial claim. He added because the rest of the pumps haven’t deviated API is there any way for accepting these pumps?
I replied “No Sir!” but inside my mind I was looking for a way or experience which could convince me that these pump will work properly.
I have attached the performance curves for ones who want to evaluate this case in detail.
Thank you all!
Mohammad
RE: pump allowable operating range
Thanks for the explaination which I'm sure reminds us all what it is like to be starting out in this field. I can't quite work out why rejecting four pumps out of the entire package and asking the supplier to come up with some alternatives would result in rejection of the vendor and a claim, but that's your issue. Hopefully they will come up with something better aligned to your requirements, but if not then you or they may need to source from elsewhere if the rest of the package is technically acceptable and good value. Like anyone or company, one company may not be able to meet ALL yur requirements in-house, but if they can do 90% then the remaining 10% may need to be placed elsewhere. Makes for another interface, but sometimes that's what you need to do.
Looking at the curves, 103 is probably OK - it's a small pump and would physically function at this duty point - which I think is where your colleague was coming from.
However 110 has an appalling efficiency (9% !!) and not much better at BEP ( 20%) so this looks like a very poor pump choice by the vendor
108 is also a decent size and has a low percent efficincy at duty point to BEP (about 60%) so an alternative should be sourced.
116 is not that big so if forced to accept would do the duty Ok
I hope that our advice has been valuable to you and good luck in getting better pumps for your required duty.
Next time try to tell us the whole story with info up front - it makes it a lot easier for us to give you a more tailored response.
My motto: Learn something new every day
Also: There's usually a good reason why everyone does it that way
RE: pump allowable operating range
Thank You!
RE: pump allowable operating range
Pumps with very low efficiencies are likely low flow pumps, which tend to be very inefficient, but let's face it, if you're only talking a 20 hp application, the low efficiency doesn't mean much in the big picture.
In life, sometimes, you have to compromise.
Instead of getting all pizzy over terminology, or insisting that your pump vendor offer you something that isn't made, why not stop and look around, ask a few questions. Maybe the retired guy actually knows what he's talking about.
RE: pump allowable operating range
there has been lots of back and forth, comments, suggestions, ideas advice, however, if you want proper advice that means something and might be helpful it is now your turn to post the pump curves and the duty / system curves superimposed over the pump curves for all conditions for those pumps you are not happy with. Having this information there are plenty of people here who can then point you in the direction with proper engineering advice based on experience instead of trying to second guess what you are talking about.
It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)