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4 pole versus 2 pole
4

4 pole versus 2 pole

4 pole versus 2 pole

(OP)
Back when I was handling contract orders for IDP, a lot of the specifications called out for 1800 rpm (4 pole) maximum speed.  Inevitably, sales and purchasing always worked around that spec. for the sake of savings, but I was wondering if that has changed at all.  Although the pump size would be larger for slower speeds (typically), the bearings, seals and such would last much longer bringing down the operating and maintenance costs.  

Any thoughts?

RE: 4 pole versus 2 pole

On the contrary the whole of life cost may be reduced because of use of a two pole speed pump. The componenets aree generally smaller and thus cost less to replace. The key is where you are located. ie cost of labour.

Two pole speed pumps are invariably more efficient than four pole so power savings accrue.

No one procrastinated their way to the top

RE: 4 pole versus 2 pole

I have heard a variety of opinions on this subject. Each person's view is shaped by their own experience.

My job is monitoring motors and assisting in motor maintance and this experience has given me a strong opinion.

2-pole machines are probably 33% of our machines but 80% of our rotating equipment problems.  

2-pole machines may save money in initial cost but will be much more painful to maintain.

RE: 4 pole versus 2 pole

It also depends on the quality of the  2 pole machine in the first place. A good 2 pole machine will out last an el cheapo 4 pole time and again.

No one procrastinated their way to the top

RE: 4 pole versus 2 pole

(OP)
stanier:  sounds like your biased to 2 pole.  Also, a good 4 pole machine will out last a cheapo 2 pole anyday.

You'll have to help me understand your comment about 2 pole being invariably more efficient than 4 pole.  It really boils down to the pump design - and since the initial price affects the desire to design primarily for 2 pole, your point maybe empirically true.  However, if pumps were designed for 4 pole speeds to begin with, that would take that out of the equation.

Having done a brief stint with preventative maintenance, I agree with electricpete.  I've done enough vibration surveys to know that higher speeds require more work.

RE: 4 pole versus 2 pole

Actually I am not biased towars 2 pole at all. However I have dealt with many public authorities over the years who blindly insist on 4 pole speeds. When a 2 pole pump gives the best engineering solution it should be used. there is just a lot of ignorance on the part of specifiers as to why a pump should be 4  or 2 pole.

In respect of maintenance is a multistage four pole pump less of a head ache compared to a single stage 2 pole?

I have used pumps running at 15000 rpm on specialist gas applications. Vibration is not an issue there.

No one procrastinated their way to the top

RE: 4 pole versus 2 pole

(OP)
stanier: fair comments. Each application should be looked at individually.  The opposite to your multistage 4 pole vs single 2 pole example is when customers pick a single 2 pole over two 4 pole pumps - blindly going for 1 pump than 2 w/o regard to operating efficiency at the required flow and pressure.

As far as high speed pumps, they need to be balanced to a gnat's .....well skip that part.  I don't know for sure, but I would guess the rotating assembly would have to be balanced to ISO 1940 G1.0 at least.  If not, I wouldn't stand next to it.

The point I'm trying to get at is with most companies feeling the economic pinch, the feasibility (at least in the bean counter's eye) to have highly specialized maintenance people is nil.  You couldn't let a high speed pump (like the one you mention) slip in terms of maintenance.  Speed does account for something.  The same mechanical seal rotating at 1750 will fail sooner than if run at 3450 (all else equal!).  Same with bearings.  Most manufacturers design a pump for a given speed (3450) and also offer it at 1750.  The seal cavity doesn't change, the bearings don't change, etc - because it isn't economically feasible to have a pattern for each speed.

RE: 4 pole versus 2 pole

Some thoughts on speed as relates to reliability.

As was mentioned, higher speed machines have tighter unbalance tolerances.  A familiar standard is 4W/N.  Iso standards are also proportional to some multiple of W/N. So we restrict unbalance by 1/Speed = 1/N and everything is fine, right?  Wrong.

Unbalance force goes with N^2 =Speed^2.  If we reduce unbalance by (1/N) we still have unbalance force increasing in proportion to N.

We're not done yet.  Rolling bearing life-time in revolutions is proportional to (Rating/Load)^3.  If load goes with N then Rolling bearing life-time in revolutions goes with 1/(N)^3.

We're not done yet.  That was rolling bearing life-time in revolutions.   Rolling bearing lifetime in YEARS is propr to (1/N) times rolling bearing lifetime in revolutions.  

Rolling bearing lifetime in years goes with (1/N)^4.

If we don't change bearings, and we double the speed and reduce the unbalance per standards, our lifetime goes to (1/2)^4 = 1/16.

OK, not fair... different bearings would be selected for high-speed machine.  That is correct.  Still there are economic pressures and I don't think you will find that high-speed machines are generally overdesigned enough to compensate for those higher stresses.

One more item:  Your mechanics have the same tools to align the 4-pole machine as they do the 2-pole machine.  In both cases they likely will expend effort to get it about as close as they can and then stop.  A good program will specify tighter tolerances for the high-speed machines but it is not likely achievble using same tools.

Maybe I have overstated or mis-stated some of these points.   People who live with the machines for the long-term see the difference. People who specify the machines never do.

High-speed machines above 3600rpm are a different ball game.  











RE: 4 pole versus 2 pole

Once again I should mention I was just expressing an opinion. No disrespect intended for anyone who carries different opinions.

If you want perspective of people who monitor/maintain equipment on 2-pole vs 4-pole, please post a question at

http://209.15.74.79/ubb2000/cgi/forumdisplay.cgi?action...=

It is a very good forum populated by vibration analysts and rotating equipment engineers.

RE: 4 pole versus 2 pole

I have been thinking about it and there is one minor detail I overlooked in my discussion that makes a huge difference in the quantitative evaluation of speed upon rolling bearing life.

I have assumed that unbalance is the only load acting upon the bearing.  In fact, if we use ISO G1.0 tolerance on 3600rpm machine, the unbalance  force is less than 4% of the weight force.

Either you guys are too uninterested (in my long discussion), or way too polite (not pointing out my error).

Anyway, regardless of my misguided attempts at quantitative calcualtion of the effects of speed, my experience remains the same as reported above.

RE: 4 pole versus 2 pole

   Power magazine's THIS MONTH'S PROBLEM in Sept. 1991 (pgs. 83-84) was "Should we specify lower speeds for centrifugal pumps?" with emphasis on 1800 RPM vs 3600 RPM. Among the 5 answers one said, "we randomly sampled 50 pumps each running at 1750 and 3600 RPM. Each speed group had pumps of identical manufacturers, models and sizes...result of our findings was that a 1750 RPM pump will run 2.54 times as long as a 3600 RPM pump." Another contributor noted that "once the 1800-2000 RPM range is exceeded, the wear rate for both impellers and housings increases rapidly because of cavitation and particle impingement." Another stated that "Vibration is more critical on a 3600 RPM pump than on an 1800 RPM pump." The 4th guy called it a draw and the 5th was all for 3600 RPM based on size and weight reductions when properly selected.
   My opinion is that 1800 RPM pumps are apt to be less troublesome if they do not have to use (1) fluid film radial/thrust bearings and/or water-lubricated mechanical face seals. Fluid film minimum thicknesses in bearings and mechanical seals become much more critical to overall reliability at lower running speeds. If the pumps are operated in pressurized systems or with ample NPSHR margins over NPSHA, then cavitation and erosion problems are practically nonexistent and 1800 or 3600 RPM pumps should be equally reliable. If noise or vibration transmission are critical to the application, then there is definite advantage for lower speeds since pumped fluid broadband excitation is a cubic function of running speed (determined by pumping power) and 18 dB reductions in flow-related noise/vibration accompany each halving of pump running speed.
   In short, the paramount consideration for pump speed selection should always be the reliability and functional needs of the particular application.
 

RE: 4 pole versus 2 pole

Many a times one does not have a choice of number of poles. Single stage pump speed is dictated more by the operating conditions than anything else. For large multi-stage pumps, lower speed can also mean more number of stages and problems with rotordynamics.

Each application requires its own consideration. No generalities can be given.

Regards,

Guru

"Evolution rather than Revolution"

RE: 4 pole versus 2 pole

(OP)
electricpete:  I was out of commission this past with a broken collarbone (motorcycling) and didn't bother to check the board.  I appreciate the repsponse and will try to get some thoughts into.

Sounds like there is a counter-point to every point, but i would be willing to bet that there is SOMETHING to it, which triggered at least an article (re: vanstoja).

However, it doesn't sound as if there has affected much in the way of pump selection these days.

RE: 4 pole versus 2 pole

HomeMadeSin,
I just read through all of the responses and had to go back to your original question to remember what you asked.  It is my experience that the bottom line to reducing expenses leads back to efficiency.  In the wastewater industry (pumping), energy usage can be many times more than initial cost or repair cost(s).  The combined hydraulic and motor efficiencies are significant factors.  On the subject of 2-Pole vs. 4-Pole, the higher speed machines tend to have more frequent service intervals (as several respnders have mentioned).
Regards,
Piffer

RE: 4 pole versus 2 pole

So the answer is to do a life cycle costing. refer www.pumpzone.com for a model.

If you work in the third world where labour is 1USD/day and all imported components have high duties and taxes the lower capex cost two pole version is a given.

In downtown New York with sky high contract labour costs and local spares then the four pole would be the answer.

You may also like to consider that your maintenance people are there anyway so geting them to do something may not actually cost you anymore.

These are the extremes I know but need to be looked at.

RE: 4 pole versus 2 pole

(OP)
I just talked with our primary motor vendor and he agreed strongly that 4 pole equipment (or more appropriately, slower equipment) outlasts 2 pole equipment.  While that is a broadcast statement, I think it is one taken from years of experience (read warranty, after-market, etc).

Now as stanier points out, if you have maintenance people anyway, so what right?  Well after doing a short stint at a paper mill, I've seen what happens to a maintenance crews over a period of cutbacks and lean times.  Joe Maintenance not only turns shafts and performs maintenance on equipment, but has to jump on the paper machine when the thread goes down.  Companies don't have as many Joe's as they once did.

Also, RotaryGuru, your point is also what I'm looking to convey.  If the conditions of service were say 100 gpm at 100 feet, a quick look at Goulds (just picking the closest catalog)3196 pump could either be a 1-1.5x6 at 3450 rpm with 5 hp motor or 2-3x10 at 1750 with a 5 hp motor.  Just an arbitrary point.  Initial cost factors would obviously favor the 6" pump as the smaller (1.375" versus 1.875" seal, coupling and baseplate.  However, what is the L10 of the smaller bearing at 3450 rpm, which is lubed (or greased) in a smaller bearing housing.  How are the axial loads and radial loads?  How does the shaft deflection affect seal life?

It would be interesting to see if any lifecycle studies have been done to compare the differences.  cost versus cost, operating and purchase.  And I definately agree that using a pump as close to BEP as possible will outweigh all other considerations.  Two pumps in series often beat 1 high speed alone in hitting the sweet spot.

RE: 4 pole versus 2 pole

In answer to Homemadesin's original question. Dont let Procurement make the decision! The decision should be made by Engineering.

its too complex an issue for the clerks of the world to decide. They have a conflict of interestin any event. They happy buying anything as long as its under budget and they get a good lunch out of it.

RE: 4 pole versus 2 pole

(OP)
stanier: I'm with you on that one.  However, in more cases than not, beancounters rule companies.....how many engineers are CEOs?

RE: 4 pole versus 2 pole

HomemadeSin,

This is a point made by many engineers but I believe that they bring it on themselves. If the engineer has any balls he will dump the whole project file on the procurement officers desk and tell him to buy what he wants and then walk away. Beancounters are just like school bulliees. Once yopu stand up to them they shrink away, the cowards that they are.

We have to remember that they have no technical skills. When push comes to shove they are smart enough to realise that they cant do it.

Simple rules:-

Dont compromise your engineering integrity
Dont sign off anything you dont believe is right
Walk away from a company that doesnt have ethics
Dont live beyond your means so that you're financially compromised before you start

If all else fails tell the client whats happening and ask him for a job. Its surprising how many clients will engage an engineer who has the guts and ethics to walk away because of what he believes in. Then you can stick to the procurement guys from the other side of the fence.

RE: 4 pole versus 2 pole

For the pumps of the type described by HomeMadeSin in his Nov5th posting differences in L10 life of the bearings will be statistically insignificant. This discussion is just academic and does not add any value to the practical aspects of how to select right pumps for a given duty. Even assuming that 5HP, 4 pole motor driven pump bearings are significantly better than the 2 pole versions, it does not translate in to significant savings to justify 4 pole pumps of this type. Note that most pumps do have installed spares.

The moment operating conditions become a little bit more respectful than indicated by HomeMadeSin, they would on their own start dictating the speeds – neither the engineers nor the bean counters (:

Regards,

Guru

"Evolution rather than Revolution"

RE: 4 pole versus 2 pole

"This discussion is just academic and does not add any value to the practical aspects of how to select right pumps for a given duty. Even assuming that 5HP, 4 pole motor driven pump bearings are significantly better than the 2 pole versions, it does not translate in to significant savings to justify 4 pole pumps of this type"

I would be interested to hear your estimates of the various costs used to reach your conclusion.

RE: 4 pole versus 2 pole

Stanier has said more than most will ever know.
Why do engineer's fold, waffle, fail in their duties?
Read what Stanier said, chew on it, the answer is there.

"Dont compromise your engineering integrity
Dont sign off anything you dont believe is right
Walk away from a company that doesnt have ethics
Dont live beyond your means so that you're financially compromised before you start"

Most engineers will NOT follow Stanier's advice because they CAN'T, they have no power to walk a higher road.  As with many other people in our present society, they value money and security NOW rather than later, they become enslaved like the others.

I know some will think Stanier off topic, but I do not.
We spend all our time arguing over the obvious and the deeper causes almost never come to the surface.

PUMPDESIGNER

RE: 4 pole versus 2 pole

(OP)
Ah, grasshopper, but you may not perceive the undertones of my intentions with this post.  I believe the beancounters are the ones one dictate 2 pole versus 4 pole.  Who writes the specifications?  Engineers.  Is the requirement to be max 1800rpm put in just for fun, I think not.  Why did the salespeople get exceptions taken on that part of the spec?  Because it allowed them to offer a CHEAPER bid!!!!!!

So, grasshopper, I agree with the fact that engineers should hold true to their opinions, but I also have worked in Sales and Marketing and while I think that a titanium pump is sexy as hell (hey, I'm a pump guy), 9 times out of 10 non-metallic works as well.  I may not like to compromise, but it is required.

I want to design our next pump for 4 pole speed because I think it is better (was looking for justification) and will have to fight the sales types from wanting to push it into 2 pole land.  The reason this gets significant is that at 2 pole speeds the pressure is 4 times that of 4 pole speeds.  Wall thickness matters.  Also, the shafting, sealing and all change.

We had a Product Development meeting yesterday and the management supports the idea of a 4 pole unit (even 6 pole is ok).  But I know the natural tendancies of distributors......

RE: 4 pole versus 2 pole

Since we're getting philosophical...

System designers/specifiers will naturally attempt to evaluate alternatives and develop a quantitative evaluation based on life cycle cost.   That we all know.

Some items are easier to quantify and some are harder.   It’s the nature of the beast.
My thought is that it varies from easiest to hardest as follows:
energy cost, maintenance and failure costs.

You can go to a catalog or oem and determine initial cost.
You can also use oem data along with calculated operating conditions to determine efficiency.
You can give some thought to redundancy and it’s effect on reliability.
But there is no book to go to to determine maintenance costs and reliability of the individual components (i.e. 2-pole vs 4-pole).    

The natural reaction of system designers may be to downplay or ignore the importance of those factors that can’t be easily quantified  (after all… what good is it if you can’t estimate it).  Usually it is the only practical approach because the info simply isn’t readily available beyond very narrow parameters like L10 life of bearings.

Homemadesin, you have gone the extra mile to really try to probe a better understanding of those maintenance costs.  I think it is a  commendable approach.  Although the system designers/specifiers may have a lot to contribute on the subject of initial cost and efficiency, there may be other sources that have valuable insight in the area of maintenance costs.  I would once again suggest you post this question on the board I mentioned above for another set of viewpoints.

RE: 4 pole versus 2 pole

electricpete is correct in all that he says, as usual.
I am watching that site pete recommended, great potential for learning there.
One little interesting thing.
What is the fallout of allowing changes too often after bidding?  A manufacturer came into my office and threatened me.  Why?  I told a specifier to not use one of their products (cheap junk), and instead told the specifier to use another product by same manufacturer (nice product).  So why the threat?  Because the manufacturer was worried that if the more expensive product was specified they would not get the job because someone would change the job out to a competitors cheap junk.
Strange world.

PUMPDESIGNER

RE: 4 pole versus 2 pole

Homemadesin,

To aid your endeavours, have you considered that the 4 pole pump with its larger inpeller etc will have a higher moment of inertia. In any waterhammer analysis you will find that the 4 pole pump will always be less susceptible to causing waterhammer excursions than the 2 pole unit on loss of power. Should there be a transient pressure event the robustness of the 2 pole unit will be challenged more than that of the 4 pole machine.

Another point is that the 2 pole pump will have nozzles far less capable of taking any load what so ever without distorting the frame. In turn will promote more wear of the seals and bearings  because of the misalignment that is caused.

In respect of life cycle costs I have been shown figures at seminars and workshops such as "the initial capex of a unit represents only 12% of the cost in its 25 year life time". A huge generalisation I know but food for thought.

RE: 4 pole versus 2 pole

Does anyone in this forum know the cost of mass produced antifriction bearings?

Regards,

Guru

"Evolution rather than Revolution"

RE: 4 pole versus 2 pole

The majority of cost involved in a bearing replacement would be manpower.

RE: 4 pole versus 2 pole

27 responses so far - that in itself is interesting, so  I decided to put in my 2 pennies worth on the subject.
As a supplier I always offered 4 pole (50Hertz) units provided they could generate the head and were a good hydraulic fit on the curve,  why did I do this - well for for 2 reasons --
1.-- I think 4 pole is less troublesome than 2 pole duty for duty in a heavy duty application.
2. -- more profit on my bottom line at the end of the day.  
My justification was less maintenance problems and maintenance costs, but then I wasn't paying the bill.
I am talking here mainly about the paper Industry - where reliability is or used to be the main criteria - we were dealing with experienced plant engineers - however today this has changed and we now have to deal with the bean counters or younger engineers who have been trained more like bean counters than practical hands-on engineers.

Having said this - I think that duty for duty, in a heavy duty application 4 pole is less trouble than 2 pole, however for lighter duty applications I would not consider 2 pole to be a problem.
At the end of the day - the defining criteria what is the duty, what is the best hydraulic selection and what are you trying to achieve.

RE: 4 pole versus 2 pole

I think that we are getting too carried away with only one parameter here. Unless 2 pole or 4 pole is the fundamentally important issue (not in my view, then the whole duty is what matters to determine which pump you choose.

I believe that for the right duty, I am perfectly capable of buying a 2 pole pump which will have a reliability more than adequate for long term continuous use. However, the most important issue about higher speed pumps is that their NPSHR will be a lot greater than that of a slower speed pump. If you buy a pump with no thought to NPSH you are more likely to get away with it at 4 pole. Also, if you buy a pump with a poor design (flexible shaft in particular - running well off its duty point is another classic) it will have problems. As Engineers we need to provide econonmic solutions, so I would always pick a well designed two pole pump if all the other (more important criteria) - NPSH, position on curve, l3/d4, bearings, detail design etc.. were acceptable.

For a given head, tip speed is going to be fairly similar whether you have a two or a 4 pole pump.
The two pole pump will have a smaller and lighter impeller and therefore does not need as big a set of bearings, so this evens out fairly well in the end (although watch out for where high axial loads are required e.g. high suction pressures as the thrust bearing loading may be of interest).
The mechanical seal on a 2pole pump will be smaller in diameter and run faster, and typically this evens out so that the PxV rating is similar on both, and you would not get more wear on the faster pump.

Four pole pumps will have a lower inlet acceleration which allows for better NPSH and maybe less erosion at the inlet if this is an issue.

There are some heads that you cannot do on a 4 pole machine, unless you go for series pumps or two stage. I would sooner have a  2pole machine than a 2 stage 4 pole machine (NPSH permitting) any day.

To be fair, if you are intent on abusing a piece of equipment:  misalignment (coupling and piping), failure to lubricate, etc.. then you will probably do better with a bigger butcher 4 pole pump, and you probably have some better career opportunities sorting out the maintenance and operation!
On the other hand if your problem on a well designed pump is that the bearings are failing through end of life, I am very impressed. L10 life even on a 2 pole pump is generally far better than people get for pump life.

Balance standard: G1 is totally over the top for 2 pole pumps. Typically G6.3 would be considered acceptable, although it is always nice to do better.

In summary, buy a well designed pump which is right for the job. Avoiding NPSH problems and running well away from BEP are probably the things that matter in determining the speed, rather than a general must be 4 pole.

Incidentally does anyone wish to join the Society for the Abolition of the "Rated point must be to the left of BEP" clause, so beloved by design contractors? The main outcome of this is that the pump can never run on its design point, and we break far more pumps from running below minimum flow.

RE: 4 pole versus 2 pole

(OP)
tonyh: good f'n post!  Thanks for bringing me back to ground.  I will say that the NPSH issue is significant, particularly for those applications that weren't sized by a hydraulic engineer or equivalent (i.e. NPSHa is not known).  It just creates a headache for the manufacturer when something doesn't go right and the application is an abortion.

Some of my current bias against 2 pole machines has to do with the applications I typically run up against.  Mostly small applications (sub-ANSI) where customers only want flow, flow and more flow.  They categorically resist buying multiple low speed pumps (very little head required in these cases) and most of the larger pumps get expensive quick.  This gap is what we intend to fill.  But back to the point, running a single high speed pump (56J motors) simply has a much lower life expectancy than two low speed pumps (same impeller, housing, etc).  And yes, I am talking about running well beyond the BEP of the high speed pump, which technically speaking is not a good thing.

Some other things you mention like l3/d4 could start a whole other thread in itself.  A simple static value used to dictate the acceptable shaft deflection is less than ideal anyway.  I think it was the PIP spec. that added l3/d4 recommendations to the ANSI spec.  So, you get pumps with l3/d4 of like 17 (way oversized bearings for the duty).  But enough digression.

I'll join you on the left of BEP thing.

RE: 4 pole versus 2 pole

Many good issues came out of this even if incompletely explained or debated.
The skill of the engineering practitioner is the only way this stuff gets sorted out and properly prioritized, and yes that person needs the beancounter.

What Stanier said still goes though.  Too many attempts with too much pressure to cut initial costs only imply that they mistrust the engineer, that the engineers does not care about initial costs, which is what Stanier was saying, you don't trust me, design it yourself.

One last thing, not doing the NPSHr calculations is simply not acceptable because putting a 4 pole double suction pump into a flooded suction or pressurized suction without limiting the margin of NPSHa over NPSHr on a water application can easily destroy the impeller quickly unless the margin reaches the point of cavitation inception (NPSHi), which will be at least NPSHr times 5, perhaps more.

PUMPDESIGNER

RE: 4 pole versus 2 pole

(OP)
PUMPDESIGNER: although more for a separate discussion, NPSH is a tacky issue.  I've worked at companies that published a complete set of performance curves for their pumps based on calculations alone - a practice that I do not condone.  Poor guys in the test stand polishing the devil out of a pump to get it to pass for the customers that did opt for performance testing, not always succeeding.  For that reason, I would only use a NPSHr (I am talking "r") calculation for info only and rely on testing to back it up.

Also, applications with NPSHa equal to 5x NPSHr (or more) are rare, from my experience and I must admit I've never seen a NPSHi acronym......

RE: 4 pole versus 2 pole

i for incipient

RE: 4 pole versus 2 pole

Not saying that Karassik is the "Pump God", but this is how he/they denote the term:

NPSHi = Net Posititive Suction Head Inception
Pump Handbook, 3rd Edition, 2.86

PUMPDESIGNER

RE: 4 pole versus 2 pole

whoops... i for inception as pointed out by pd.
inception as in inception of cavitation.

(sorry to beat a dead horse)

RE: 4 pole versus 2 pole

electricpete, you are definitely one of the smartest guys on this site, I'll bet that was the first mistake you made this year, though I am saddened by the tininess of it though, hope to catch you big some day, probably will go the other way though.

PUMPDESIGNER

RE: 4 pole versus 2 pole

HomeMadeSin,
If you have Pump Handbook 3rd Edition read the section I referenced: 2.86.  Good statements regarding excessive margins of NPSHa over NPSHr.  By the way, does your handle have any specific meaning?

PUMPDESIGNER

RE: 4 pole versus 2 pole

"Rated point must be to the left of BEP"   We chucked that concept longtime ago. Now-a-days, related clauses read something like:

a) Rated point to be within 70-110% of BEP.
b) For rated capacities larger than XXXXX m3/h, rtaed point to be within 10% of BEP.

Regards,

Guru

"Evolution rather than Revolution"

RE: 4 pole versus 2 pole

(OP)
PUMPDESIGNER: I have the 3rd Edition, although I just got a few months ago.  Up to that point, I was still on the 1st Edition, back when HE :)worked for Worthington.  It seems they identified the term between 1st and 3rd ed., not that I am that proficient in that section of the back anyway.

My handle is insignificant.  There was a saying my grandmother had about something being ugly as home-made sin.  I've made a few things for engineering classes that I would label that ugly, so it stuck.

RE: 4 pole versus 2 pole

I own and operate a small pump repair shop and know from experience that if all the pumps were 1800 RPM, the repair intervals, at the very least, would double!

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