[CSP 750] the joint is badly assembled

[Eve]

/!\caution/!\

Hello I'm french boy and I found its

Look at the lip seals between the engine and water
at the left correctly assembled & at the right CSystem




CSystem assembled:

















it is catastrophic for the motor


The good assembly must be










comparison:





In the first picture:
The pressure of water will exert a perpendicular force to the lip seals and will increase the sealing.

In the second picture:
the pressure of water will push the lip seal and will pass in the motor casing

sorry for my bad english

[jaydee]

I assume thats your pump in the pictures above? Is this an isolated thing or are ALL pumps built this way? Anyone else have similar issues?

[Eve]

Yes all pump

CSystem 's answer: (Dave)

I can not discuss our engineering, however the seal is in the proper
orientation for the types if pressures it accouters (negative).

We will not send any more motors, without examining the complete failed unit
first. That means the full pump assembles.

Pfff

[pHaestus]

Can't have too many of those with a 50k MTBF

[BillA]

Originally Posted by pHaestus

Can't have too many of those with a 50k MTBF

lol
not a single fanboy wanted to listen, 'thought' being totally excluded from the fanboy universe

hi ho

[melpheos]

Originally Posted by unregistered

lol
not a single fanboy wanted to listen, 'thought' being totally excluded from the fanboy universe

hi ho

can we have your point of view on this ?

I am the lucky one :shrug: who made the grouped command from which the pump in picture is issued

[lolito_fr]

I guess now we know why C-systems specifically recommended not to put these pumps in series

From what I've read about lip seals, the best are only good for 2500hrs...
The failure mechanism is quite interesting - how the rubber can "eat" the shaft

[pHaestus]

BTW thanks for posting this here EVE and welcome to the Proforums.

[Eve]

THX and sorry for the picture

[BillA]

my 'point of view' has been stated several times
a 50,000 hr MTBF on the motor says nothing about the pump, do read the original thread
mechanical seals are the problem, nothing new here, nothing at all
then read Roscal's article on pumps, a paddle wheel impeller is all about cheap - not efficiency or high performance

the net result is another mediocre cheap pump (with obviously poor QC),
and a ready market - DIYers whose ignorance supports so many products

[killernoodle]

I can not discuss our engineering, however the seal is in the proper
orientation for the types if pressures it accouters (negative).

We will not send any more motors, without examining the complete failed unit
first. That means the full pump assembles.

This is what is going on, it is the proper type of seal. Because it is a centrifugal pump, the water closest to the center of the impellor will naturally have a negative pressure, and as water is slung to the outside of the pump it will hit the wall and gain pressure. Thus, the seal is correctly oriented on the shaft to put pressure on the shaft and seal it properly.

Just think about it for a second before you respond to defend yourself and hours of CAD drawing

C-Systems used the right seal orientation.

[Eve]

not the centrifugal force doesn't creates low pressure zone
Pwater > Patmospheric

[CoolROD]

I have been mulling over the same thing -low pressure at the center of the impeller. The seal would still have to stand static pressure of the rated head when not running.

[lolito_fr]

the water closest to the center of the impellor will naturally have a negative pressure

If your pump is sucking, then yeah. In most cases we design our loops to avoid having negative pressure at the pump (large dia inlet pipe, pump located below vented res, etc) as we know that this is bad.
There is a pressure difference between the center and periphery of the rotor, but if the pump outlet is restricted then the pressure difference between the pump case and atmospheric is positive.

edit: Eve, ton plugin c'est Spellbound

[BillA]

nope, crack the seal on the pump inlet and watch it suck air
is it still negative behind the impeller (given their design) ? sure

[melpheos]

Originally Posted by unregistered

nope, crack the seal on the pump inlet and watch it suck air
is it still negative behind the impeller (given their design) ? sure

Is it a question or an affirmation ???
Do you think you might have as Dave from c-systems quoted "negative pressure in the main chamber" ?

[lolito_fr]

sounds very much like an affirmation

So this implies that the C-system implementation is the correct one?
-pumps I have seen have it the other way round
but then they were force fed I suppose (submerged, or fat pipe & below water line)

[am slowly realising that the second part of my above argument doesnt "hold water" (sorry) too well.]

[CoolROD]

I think that the seal orientation may be correct. It would keep motor grease / debris out of the system. Static seal preload may have been intended to provide the seal pressure for the lip seal in a non-running situation. I don't know -I am just trying to back engineer the thing...I work with hydraulics and seals for a living, but will not try and claim to be an authority on the subject although I have engineered innovative lip seals for hydraulic systems.

I will also avoid the above comment about lip seals leaking / failing...
Sure they are mechanical seals that are prone to wear, aging, and fatigue, but, I have some that have run 20000 hours...and are not leaking.

[CoolROD]

BTW Eve -Welcome to the forum. Nice drawings and Killer high-res photos.

[nicozeg]

Up to now I have seen an impressive 3d presentation about seal theory, but the main thing has not being menctioned :

Does one of this catastrophic wet motor events really happened?

[Hotseat]

Bill, I can not for the life of me believe your an engineer, and not know that area of a pump is zero or negative pressure !


**Sorry but this is too much even for me

[BillA]

Originally Posted by unregistered

nope, crack the seal on the pump inlet and watch it suck air
is it still negative behind the impeller (given their design) ? sure

seems perfectly clear to me
in fact I don't know how it could be stated more clearly

[Cathar]

Originally Posted by unregistered

seems perfectly clear to me
in fact I don't know how it could be stated more clearly

A ringing endorsement from engineer to "engineer" about how said pumps really do have a 50000hr MTBF, with perfect quality control, and have no design faults or caveats to be wary of for the naive end-user perhaps?

[BillA]

you have me confused Cathar
??
what was clearly stated by me was that this pump does NOT have a 50,000 MTBF, nor good QC
and now it is clear why the pumps cannot be used in series

ah, you mean the mfgr should have been more candid ?
but did they not get lots of orders ?
and has the business not just been sold ?
let me guess who is the winner ?

and people wonder why I'm cynical . . .

[Hotseat]

I really don't want to comment further, as I was taught, as most engineers have been, not to poke at other emgineers work. This is not a way for a professional to act. Imagine the results if you seen two doctors arguing in public.

But seems Bill has nothing better to do then make himself out to be an "expert" in just about everything

Impellers...... Paddle wheel is best, at this diameter / rpm, has nothing to do with being "cheap".

You will notice, almost all pumps of this diameter / rpm have paddle wheels... do you think a company would spend 1000's of dollars on a mould, and not use the proper design?

The reason you use a paddle is because of diameter / rpm. The inner part of the small impeller is traveling at low velocity, and therefore has no effect, in fact it is "in the way". This is true for most of the impeller other then the outer edge. As you increase diameter, then you can see an increase eff with curved or turbine type units (true impellers). This is also true at higher rpms.

Seals - That is whole different issue, and a damn interesting engineering field.
The larger a seal, the greater the ware. But this is not do to contact area, but the total area exposed to pressure. As you increase in size, you can not avoid the exposed area increase, as a squared function. So when you get to a certain size, you must use a mechanical seal, which reduces the exposed area and corrects for ware.The reverse is also true

So the "trick" is rpm, impeller, and seal combo when it comes to pump design.
You can not point at any one pump part and say "this is wrong" without analysis of the whole unit. But any good engineer knows this

Guys, there are VERY good engineering books, on just about EVERYTHING you discuss in these forums, including cooling blocks, the science of which is well known and not "voodoo" as some make it out here.

Please read, learn, and enjoy the work 1000's of engineers and scientist have done over hundered of years. Even better, get a true understanding, and improve on past work. This is the goal that drives engineers....well the ones I know