Double Volute Pumps 2

[PUMPDESIGNER]

Looking for manufacturers of end suction double volute pumps.
Some manufacturers still make end suction double volute pumps, but only in larger sizes. Goulds for instance makes double volutes but only three sizes: 1000 gpm @ 240' TDH, 2000 gpm @ 120' TDH, and 4500 gpm @ 100' TDH.

We need pumps in the 100-600 gpm range, heads 150' TDH to 300' TDH.

I have not found one single manufacturer of smaller double volute pumps.

Any help at all would be appreciated.

PUMPDESIGNER

 

[Artisi]

Can't help with any manufacturers - but I'm interested in why you are trying to source double volute in such small units.

Naresuan University
Phitsanulok
Thailand

 

[jet1749]

Check out Sterling Fluid Systems in the UK for their Q series double/triple volute pumps, they are a bit of an elderly design and perhaps do not conform to either API/ANSI/ISO or DIN standards. They are a foot mounted bearing bracket, non back pull-out unit. I believe Sterling have representation in the US.

 

[PUMPDESIGNER]

Hello Artisi,

You are a curious fellow. A lifetime of that stuff and you probably know a lot.

As you know, double volutes are incredibly balanced, practically no radial thrust at any flow rate. Costs a few points in efficiency, cost a little more to make. Sooo, they have dissappeared from the market place. I and others have cried about this decline in the pump industry.

Anyway, talking to engineers in a very large pump company, they claimed that radial thrust is only a problem in large pumps, but that is not true.

Our experience with end suction volute casing pumps is that systems with variable flow rates, say 30% of BEP up to BEP, the bearings do not last more than about 5 years maximum, and a few fail in 1 year, probably because they operated for very long periods at 30% of BEP.

We have decided this is due to radial thrust loads, and strangly, the front bearing intended to take the radial thrust load is not the bearing that fails, it is the smaller back bearing, probably the vibration and torque is not entirely negated by the huge front bearing and makes it back to the tiny little back bearing and kills it.

For five years we have been refusing to sell the larger volutes and instead have gone to turbines and multistage pumps with diffusers to eliminate radial thrust. But we have walked away from a lot of work because our systems cost much more. In some cases, I would like to be more competitive with the cheap and dirty single volute guys with their extremely high efficiencies and yet for a few bucks more we can compete and not have short lived motors like the other guys.

We recently walked away from a $100,000 job because we did not want anyone to be angry with us over pump motors and bearings that lasted only 1-3 years. When we asked them if that was acceptable they said it was, but still we just could not get ourselves to do it. Imagine your name on something that fails like clockwork every three years where a quality product would last ten-twenty years. And I must remind myself of this one thing, those people that said 2 years of life was Ok, why are they coming to me when they already are in that mode now? Because they are tired of the short lived pumps and are constantly replacing the entire pump sets, and they admitted that to me. Our price drove them away. But, with a double volute I can compete and know that the pump will last 10-20 years.

Is that why some cry about the loss of double volutes in the market place? If I cannot find small double volutes, I may design and make my own, I can sell it.

God Bless.

PUMPDESIGNER

 

[Artisi]

Hi Pumpdesigner
I understand what you are saying regarding short pump bearing life, but be a salesman and sell - sell - sell, if short bearing life is an issue with the bid analysis - offer a "free" set bearings as part of your package.

I guess you are talking about "motor-pumps" ie, pumps direct coupled to the motor flange if this is the case why not change to bearing frame mounted pumps - plenty of units out there capable of running for 10 years -it's only 87600 operating hrs 24/365/10 years - running off BEP even if you allowed for 50% derating it's a B10 life of 170,000 hrs - achievable with the right manufacturer and bearing selection.

Talking about bearing frame mounted pumps not motor-pumps.
A point to consider- is the maintenace of the plant upto offering the correct maintenance periods etc to give 10 years bearing life - my experience is that in MOST CASES the bearing fail from causes other than bearing load or exceeding their B10 life.

If you are stuck with motor-pumps can you upgrade the bearings or even modify the bearing arrangement or size.

otherwise join the mob - and sell what they are selling BUT give better service - even maintenance service with change over pumps that can be replaced prior to any unscheduled failure.



Naresuan University
Phitsanulok
Thailand

 

[PUMPDESIGNER]

I like your ideas Artisi, no one wants to sell any more.
When they come along we quote them and try to point out where they are at and where we would like to take them.
We lose some big ones, but we do see them come back now and then, and we also get ideas for new product.
Right now I am considering making our own double volutes.
We are finishing up one pump now, could start a double volute project.

You are correct, this is that little close-coupled JP/JM frame pump motor market, low end stuff. But it does not have to be so dirty and so lowly, we are trying to make it a good place to be.

PUMPDESIGNER

 

[PUMPDESIGNER]

Thank you jet1749 for the reference.
Plowed through their site, could not find any mention of double volute.
Did download their pump book. The Brits are excellent technical writers and I look forward to reading it.

PUMPDESIGNER

 

[vanstoja]

Your description of non-driveend(NDE) motor rolling element bearing premature failures suggests that your overload problems may be due to axial hydraulic thrust(AHT) rather than radial hydraulic thrust(RHT) which would make your focus on double volutes misplaced as a solution. RHT loading is easily calculable and you should be able to select drivemotors for your pumps that have sufficient shaft strength to prevent RHT overloading as well as providing the needed pumping horsepower. AHT is much more difficult to calculate and transient operations such as startups are apt to reverse normal axial thrust load direction (usually toward the impeller eye). See recent thread407-110575 on vertical pump upthrust loads during startups. Rolling element thrust bearings are generally unidirectional to my knowledge and will not take kindly to reversed axial thrust loading such as may occur during pump starts. From a radial load standpoint, motor unbalanced magnetic thrust(UMP) is a real, easily overlooked concern if motor shafts are not stiff enough to prevent deflection of the rotor core into the airgap clearance. This is a negative spring load, not easily calculated, which increases dramatically with increased rotor radial deflection.
I applaud your engineering scruples that place product reliability above profit motives and fully appreciate your difficult position as a pump-driver-controller unit middleman. Strictly speaking, you are neither a designer of pumps/drivers nor an end-user, but rather a procurer of the best of both worlds for your end-user customers. In such a position, you are faced with the daunting task of interfacing two components that must work together, presumably without benefit of a standardized specification that can be laid upon the pump and driver manufacturers and possibly also without adequate information from the end users to fully anticipate the uses and misuses they will subject the integrated unit to. I had a similar pump-motor design procurement job for more than 40 years but benefited from standarized military specifications (which we updated and partly controlled) and adequate information from the end-users that enabled specifications to be adjusted from project to project for special, off-design and transient operating conditions which were based on operating histories scrupulously recorded and periodically reported by the operators who had some accountability to us. On a long term basis, such a system might be a worthwhile objective for your company. In your own defence, you need to become nearly as expert as your pump and driver designers in order to adequately judge design quality for the particular application. I spent 40 plus years trying to do just that and did a lot of technical publications reading and collecting to acquire expertise necessary for such a demanding technical-middleman position.

 

[PUMPDESIGNER]

vanstoja,
You have me and my job task figured out correctly.
Not many would see that.
Thank you for alerting me to the possibility of axial thrust. I ignored that because I thought the very large bearing on the pump side of the motor (JM and JP frames), handled most of that issue in addition to radial thrust. I will look into that, not sure if the problem is tractible.

We do know this.

JP/JM frame pump motors work great on close coupled systems, often last for 10-20 years or more with little or no maintenance. We come across these in the field all the time, where the motor is obviously original was never worked on or changed.

However, that only applies to small stuff, 2hp through 10hp or perhaps 15hp. Larger than that and the whole thing changes, motors are throw away and do not last at all. We know and can estimate by calculation the radial thrust easily enough. Axial thrust? Could be a problem too.

I was following the lead of McNally, who complains about the "disappearance" of Double Volutes from the marketplace, I personally think he was correct to complain.



PUMPDESIGNER

 

[Artisi]

Folowing on from Vanstoja who has made some very valid points in his response, I would suggest that you have a bearing failure analysis undertaken by a specialist to assertain what in fact is the failure mode of the bearing/s.
In the cases you are generally talking about, we know that the pump is the cause of the problem - so forget the pump at this point because there is nothing we can do until we understand why the bearings failed - axial or radial load -ball or roller skidding - insufficient B10 life for the application etc.
I am a firm believer in the chicken and egg theory, "what came first" -- therefore look at the bearing failure mode -once you fully understand this you can then move on to a remedy.

This is a simplistic approach of course without looking at all the other possiblities, is it the right equipment, was it selected properly, is the actual duty what was spec'ed intially etc and so on.

Just to move on a bit - for any application that has a wide range of duties in terms of H-Q - ie, one that is likely to operate well left of BEP for any period of time -I would, if possible, probably select a pump that would operate on both sides of BEP - how far right / left of BEP would be a decision based on the known facts and the pump characteristics - as you have said before - the loss of a few points of efficiency in these small units would probably outway the failures.

By all means develop a double / triple volute pump range if you have the time and money and need the headaches of a pump manufacturer - but how many pump sizes do you need - you can bet the first job that comes along you won't have a hydraulic fit for it - so back to square-one again - and a compromise on selection.

Naresuan University
Phitsanulok
Thailand

 

[rmw]

Go to

http://www.naglepumps.com,

and contact them and ask them if they ever put a double volute pump impeller in one of their pumps, or if they could. Since they make a bottom suction, and an optional top suction, they might be able to do both at the same time.

rmw

 

[PUMPDESIGNER]

Good idea about bearing analyses artisi. I will follow through on that.

PUMPDESIGNER