Re: Metering Pump Gears

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Posted by d_ on February 24, 2001 at 09:01:11:

In Reply to: Re: Metering Pump Gears posted by Bill S on February 22, 2001 at 08:20:01:

This one is a case of that the coarse pitch one,
with 6.35 teeth per inch of pitch diameter (4mod)
when compared with the finer pitch one with 10.16
teeth per inch of pitch diameter(2.5mod), but
having the restriction of having approx. the same
nominal outside diameter must have greater
differences in their number of teeth (11 vs 18)
between them, and the consequence of this is the
problem. While it is the undercut nature of the
cycloid that is the reason gears work well as
pumps, there is a lot of difference between the
paths the two sets take when you look at any
point on the profile as it is meshing. As can
be seen looking at a point on the tooth tip, on
the 11 tooth set the path taken is more looped
and extreme, so the sliding velocities around
this trochoid must be greater as the teeth mesh
at the same rotational velocity as the 18 teeth
one. The answer-not easy if the size constraint
is an issue-lower the actual velocity at the tip
through changing the module and raising the
number of teeth a bit. As a consequence of
larger tooth number, the tip path is less extreme.
Make the volume difference up with frace width
of the pump gear set.

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