centrifugal pumps - what is the purpose for the clutch?

When you take your average powerhead apart you will
probably notice that the impeller is attached to the
shaft with a kind of clutch allowing it to rotate
freely on the shaft about 3/4 of the whole turn...

Is this to allow pump a sure start or does it play
any other role ? How is this "feature" called in
technical plumbing terms and where can I read more
about theory of centrifugal pump operation ?

Nobody knows what is the purpose of this 3/4 turn lose shaft attachment ?

"Pszemol" wrote in message ...
When you take your average powerhead apart you will
probably notice that the impeller is attached to the
shaft with a kind of clutch allowing it to rotate
freely on the shaft about 3/4 of the whole turn...

Is this to allow pump a sure start or does it play
any other role ? How is this "feature" called in
technical plumbing terms and where can I read more
about theory of centrifugal pump operation ?

Powerheads, and submersable pumps work on a vibrating back
and forth movement. This makes them easy to hang up. If
the impeller was solidly attached to the the magnet, the
magnet would have a hard time starting. The clutch allows
the magnet to get one 180 degree turn before putting a
load on it. It also has another advantage. If the
something gets sucked in, and jams in the impeller, it
allows the magnet to spin back and forth and work the jam
loose.

Wayne Sallee
Wayne's Pets



Pszemol wrote on 5/14/2006 12:37 PM:
When you take your average powerhead apart you will
probably notice that the impeller is attached to the
shaft with a kind of clutch allowing it to rotate
freely on the shaft about 3/4 of the whole turn...

Is this to allow pump a sure start or does it play
any other role ? How is this "feature" called in
technical plumbing terms and where can I read more
about theory of centrifugal pump operation ?

It's also a 50/50 chance on wich way the impeller will
spin when you start it up. In my live rock bin I have a
submersable pump to circulate the water. I made an
adjustable venturi for it. If I tweek the venturi to
produce max bubbles, and then turn the pump of and back
on, if the pump spins the opposite direction, the venturi
does not produce as much bubbles. I can then retweek the
venturi, or just turn the pump on and off until it spins
in the previous direction.

Wayne Sallee
Wayne's Pets



Wayne Sallee wrote on 5/15/2006 11:01 AM:
Powerheads, and submersable pumps work on a vibrating back and forth
movement. This makes them easy to hang up. If the impeller was solidly
attached to the the magnet, the magnet would have a hard time starting.
The clutch allows the magnet to get one 180 degree turn before putting a
load on it. It also has another advantage. If the something gets sucked
in, and jams in the impeller, it allows the magnet to spin back and
forth and work the jam loose.

Wayne Sallee
Wayne's Pets



Pszemol wrote on 5/14/2006 12:37 PM:
When you take your average powerhead apart you will
probably notice that the impeller is attached to the
shaft with a kind of clutch allowing it to rotate
freely on the shaft about 3/4 of the whole turn...

Is this to allow pump a sure start or does it play
any other role ? How is this "feature" called in
technical plumbing terms and where can I read more
about theory of centrifugal pump operation ?