Why Apex Seals Fail

[Barry Bordes]

Originally Posted by vex

How did I miss this thread?

Let me see if I can help in adding my schooling into the mix (Hurrah for Fluid Dynamics being applicable in all situations dealing with flow).

I think the ROOT cause of the flow issue is going to take some exploring. First and foremost what do the individual passages look like? I notice from the picture you appear to have a lot of, what appears to be, leakage between the sideplate and the rotor housing. If that's just an illusion then we can forego that issue. However if it's not I think a pressure differential is developing prior to the passage.

It is an illusion, there is no leakage. The #5 passage is just too small.

What I mean by that is that if you have a single source flowing unevenly into the various passages the incompressible nature of the fluid is going to dictate that the area with the higher pressure is going to output the more mass of the fluid (all other things being equal). Consequently ensuring you're getting an equal flow rate prior to the passage entrance would be paramount.

The water is entering through the normal pump passage.

If however there is no leakage and the input is simply just feeding it through the water ports where the waterpump seals, then the issue is indeed hardware related. Consequently since we can assume a uniform pressure distribution (not only for this experiment but for the real world application) we can see that the differences is going to be directly related to the hydraulic diameter and boundary layer conditions of the passages. This provides us with an easy enough solution as well.

First and foremost; enlarging the hydraulic diameter of the passages will allow for a more unified flow condition between all ports in question. There remains however a finite amount of space to achieve that. The other option that can be excersized as well would be to instill a turbulent boundary layer on only some of the passages.

Why only some? Think of it this way: we have a large passage that is putting out a lot of fluid. The issue is attempting to balance the passages to output the same amount of fluid at the end of the day. To do this we can lower the friction a majority of the fluid is exposed to in the other passages, in essence allowing for a faster flow to be achieved on smaller passages, while the undisturbed boundary layer on the larger passage causes the flow to slow down when compared to the tripped boundary layer of the smaller passages.

The solution will consist of finding the appropriate balance of the two.

The experiment is a simple but elegant representation.

Barry