Brecab wrote:

Any good ideas on how to drive a vacuum pump off a 13b? Is there anybody
already doing it? If so, I would like to see a picture or drawing if

someone

has the time to post it, it would be greatly appreciated. I'm trying to

come

up with a simple solution but I haven't had much luck so far. I hate to

go

all electric, I feel like I'd be putting all my eggs in one basket If

you

know what I mean.

Rumor has it that a smog pump works great. The downside is it is
a bit heavy at 8 pounds.

Ed Anderson wrote:

 Hi Brecab,

    I designed a fitting that permitted me to drive an Aircraft Vac pump
using a belt and pulley.  However, after a year and two vacuum pumps I
switched to the Mazda air/smog pump with much better results, the only down
side being its heavier weight.

   The problem with using an aircraft vaccum pump is that most (for
Lycomings) are limited to 3800 rpm or less.  I have verified that by
destroying two of them.  If you use large enough pulley to slow the vac pump
rpm to 3800 (or less) at 5800-6000 engin rpm then the at slower engine
speeds the pump does not spin fast enough to produce the needed vacuum.  If
you select the pulley size so that you have good vac at lower engine rpm
then it spins too fast at high engine rpm and soon becomes graphite powder.

  So despite the heavier weight of the air pump, it produces excellent vac
even at 1200 rpm idle.  Thats my 0.02

Ed
Ed Anderson
305 Reefton Rd
Matthews NC 28104-0569
eanderson@carolina.rr.com

Ed how did you deal with the belt side loads in the pump? The pump
on my Continental O-470 is driven off an accessory drive that has the bearings
built in. The pump itself has no bearings to speak of. 

The range of prop RPM should be the same in both a geared
Mazda and a direct drive AC engine. Unless of course you are cruising
the Mazda at way less than 50% power. I think something else was going
on with your AC pump failure situation. There is a guy from Ontario
Canada that is running a V6 in a pusher that uses a belt drive AC
vacuum pump. He was at OSH this year. He had to fabricate a bearing
housing for the AC vacuum pump. I have a picture of the pump
around here someplace.

Paul Lamar
 
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