centrifugal pump design 1

[qualicas]

I have been involved cars as a hobby for some time. I recently obtained a 1995 BMW. One of its weak points is the cooling system. I'm rebuilding the engine and was just looking at how the water pump fits. It is a centrifugal design pump. Water has to run through a fairly small opening to get to the impeller. It comes in next to the shaft rather than opposite the impeller. Then the impeller is all the way into the block with no pump housing around it. The idea here is that the water will just fling itself away from the impeller in all directions I guess. I've never seen a pump designed like this. Is that an acceptable design or did someone at BMW not know what they were doing??

 

[itsmoked]

It's common in automotive applications and works acceptably.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[Artisi]

I think you can assume that BMW have enough expertise in know howing to design a pump for the cooling system on your vehicle.

 

[qualicas]

Artisi
I assumed they knew what they were doing as well. The fact remains that if you look on any BMW discussion forum, the single biggest problem is the cooling system. Many people have trouble bleeding it with the result that the engine overheats. When it over heats it warps the head and blows a head gasket.
Itsmoked, Sort of good to know that it is a common design among other manufacturers. I would think cavitation is common in this design as well, since the intake is quite small and the outlet is the entire block.
Just seems like a very poor design. It is better now though. They originally made the pump impeller out of plastic and they used to break without warning causing an overheat condition. Don't get me wrong with the plastic though. I'm in the injection molding business and I've seen my share of bad part design from people/companies that should have known better.

 

[itsmoked]

It is a poor design in my opinion. But it's a cheap design getting the volute for almost free. Car makers are driven by costs more than any other, so in the mix it's an "acceptable" design.

As for the prime/air/destruction issue, there are several things like that in most autos. If you don't follow the rules of how to get out the trapped air, and how you monitor the engine long enough to KNOW the water is circulating properly, you do indeed risk failure.

So if a procedure is done wrong and failure results it's not really the design's fault.

That said, Renault did the same obnoxious thing on my R10. The water pump was in the head. I had horrible heating problems. Turned out the volute was eroded into having an internal bypass. I put a plate over it and fitted a bronze, belt driven Teel centrifugal pump next to the generator. I never had anymore circulation issues.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[qualicas]

Itsmoked
I was sort of thinking of doing a similar thing add a separate pump and be done with it. Although, I'll probably just try the original setup first since I have a new pump.
But now I sure know why there are problems.
Thanks for your help.

 

[hydromech]

It is more likely the case that the person who designed the block did not know what he was doing when he modelled the water pump volute.

It is not limited to BMW either, although they may well be one of the worst. We make loads(300,000+) of water pumps for automotive and commercial diesel engines and it is surprising how many engine designers add inefficient or unsuitable water pumps to their engines.

It seems that they design the engine and then suddenly remember to add a water pump to cool it, even though there is no room for a water pump.

Adrian

 

[itsmoked]

At least I'm pleased with my old 85 FORD diesel. The water pump moves a true 55GPM thru the radiator and block.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[qualicas]

Hydromech
I think you hit the nail on the head. Someone wasn't thinking about water pumps. Now the suction side of the pump sucks water from the head, through a gasket that is prone to fail into an aluminum housing and back into the block. When the thermostat opens, the water gets SUCKED through the thermostat and into the water pump.
I'm just happy to find that I'm not the crazy one here and have everyone say it was a perfect design. Now I know what I'm up against, I deal with it.