jon928se

It's a centrifugal pump so the vanes are radial and curved so on their own impart no thrust in either direction. There might be some force along the axis of the pump shaft imparted by water flowing over the "top" of the vanes (between the vanes and the cone shaped surface in the block) but my fluid dynamics is too rusty to figure out if that would be a positive or negative pressure.

If the vanes were reversed the water would flow in the wrong direction.

Jfrahm

FWIW, The pump I recently pulled off my Murf car appears to be original from 1987 and I believe it was made by GEBA by virtue of the GEBA diamond logo in the casting as well as the "Triangle-P" OEM part marking. It has a metal impeller, naturally.

P.S. Does anyone know the name of the triangle-P mark?
-Joel.

ROG100

Joel,
That does not sound like a GEBA pump at all - see my earlier comments about GEBA markings. As they seem to have only been selling them for a year also unlikely.

69gaugeman

I'm with Greg and am one who also doesn't believe the impellers being plastic is the solution.

polecat702

Why not get one of Ed's Guardian pumps, and forget about it? Mine has been run hard in the Nevada "furnace heat" for 3 years, and still going strong. Cost is comparable to Laso, Geba.

Dave928S

Open face impeller pumps always grind into the front pump case if the bearings are worn, as there is always a negative pressure at the intake and eye of the impeller, and a positive pressure behind. The suction literally draws the impeller into the front plate (block in this case), and this only happens because bearing slop allows it. A side effect of that axial movement is that it makes the seal leak more, which trashes the bearings more ... and then it's all over and leaking like a sieve.

Closed face impellers don't 'machine' the front plate (they just score it or jam), and give more consistent and better flow/pressure characteristics, because the loss/mixing at the front of the vane, because of the necessary working clearance, is eliminated.

MjRocket

How does one go about getting their hands on one of Ed's pumps?

Dave928S

Contact Ed who developed the pump. Here's thread with all the details .... https://rennlist.com/forums/928-foru...ics-added.html ... and here's his website ... http://perfexmfg.com/

daveo90s4

Hi Jon

Points noted. But just to be pedantic, not sure you're right about 'if the vanes were reversed the water would flow in the wrong direction'. The pump would still be rotating in the original direction so would still push the water in the same original direction. No? Just markedly less efficiently. 😀

Dave

69gaugeman

Yes, but a closed face impeller is MUCH more expensive to manufacture.

It would be less efficient, but you have to understand the water gets sucked into the center of the impeller then 'thrown' outward in the pump action. If you angled the vanes enough to counter the vacuum at the center it would just circulate the water around the impeller. So no, it's not really feasible to do that.

Dave928S

I wasn't suggesting that a closed face impeller should be adopted in a 928 pump, but that there are alternative design features, which eliminate some drawbacks.

On the above point that you make, I beg to differ. Having had personal hands-on experience in pump design, research, development, and manufacture, including production of dies for injection moulding of thermoplastic pump components; I can confidently say that the cost difference between one piece in a die for an open, and two for a closed in the same die is trivial. Add one more operation to put the two pieces together and its still trivial.

On your second point, I think the accurate answer is more likely ... 'it depends on many design features'. Whilst your scenario of zero net output is possible, it is also just as plausible that the flow is reversed and diminished. There are so many variables that the only way of being certain is to try it ... I have on some closed vane pumps and they pumped in reverse.

FredR

Good to see you boys talking about pump design. If the pump is run in reverse it will still pump but the efficiency goes down the pan and in practical terms will likely be useless.

Arguably there is a design flaw in the 928 pump volute. For pumps to be efficient they need very tight clearances between the impeller and the volute. If a pump bearing fails it rapidly wants to become a lathe so to protect against serious casing damage industrial pumps are kitted with what we call "wear rings". If these rings are compromised during a bearing failure they are pulled and replaced.

In the case of our engines it is probably not practical to build such into the design given the small dimension involved. That being said and thinking about it a bit. that leaves me wondering what Greg [Brown] does when he repairs a damaged casing. I suspect he is machining the pump volute and probably inserting what in effect will be a wear ring to reinstate the correct clearances between the casing and the pump impeller given it is not possible to mount the pump further inboard.

The plastic impeller was a logical design to prevent the gouging of the seat. I have lost two plastic impellers over the last 16 years- both pumps had perfect bearings/seals as I could tell but the impellers let go- on one of them the hub cracked.

Maybe sound repairs are possible at a realistic price?

Rgds

Fred

Landseer

An insert is utilized during repair...

http://www.dwaynesgarage.norcal928.o...k%20Repair.htm

FredR

A very smart approach to solving what would otherwise be a coffee table by now. That is what I call lateral thinking and best of all it can be done in-situ!

If all we are going to get are water pumps with metal impellers then doubtless this procedure is going to see more service unless the manufacturers can stop the self destruct tendency.

Rgds