Hi:
I have a strange problem with my '96 Whirlpool Quietpartner 980
dishwasher. At the beginning of each wash or rinse cycle, the tub is
filled, and the pump should start pushing water up through the columns
and through the arms causing them to spin. When this dishwasher was new,
the "agitating" would begin before the timed fill cycle was even
complete. Now, the agitating occurs from 30 seconds to a couple minutes
after the tub has filled! If you open the door real quick to see what is
going on in there while it is "trying" to start, you see that the water
has been swirling around in the bottom of the tub, and a few air bubbles
come up to the surface of the water. Here is the kicker.... If you then
shut the door, the agitating starts IMMEDIATELY. In fact, this hack
solution works all the time. All you have to do when it is "stuck", is
just open and close the door for a second, and then is starts up
immediately. When it is in the "stuck" state, the motor seems to be
turning just fine. It doesn't sound strained at all. It seems to me that
the impeller is cavitating.

OK, so I got the repair manual, and tore down the pump as far as I could
from the top. (Actually, you can get quite a ways into it from the top!)
There are a couple things that are suspicious to me. Unfortunately, the
darn repair manual is a "tear down, put together" tutorial that doesn't
explain what everything does. Anyway, there is a valve which consists of
a plunger, spring, and rubber end, and also a check valve. These live in
the donut shaped white plastic "torus" or "seperator" as Whirlpool calls
it. I have no idea what these do. The manual is no help. They look fine.
There is nothing obviously wrong, or no visible gunk anywhere. I suspect
these because the problem seems to me like it could be caused by the
pump getting stuck in this "cavitating" state, then when the door is
opened and closed, the air bubbles go to the surface, and then when the
thing is restarted, it takes right off. Maybe one of these vavles is
sticking???

BTW, I also suspected that maybe the tub did not fill with enough water,
but I tried prefilling with a couple extra gallons and this did not
help. Also, this theory does not fit with the "open and shut the door"
hack.

So, my first question is does anyone know what these things do?
Second question would be if anyone knows what specifically would cause
the problem?