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'Physics question, air flow and valve...'
2005\07\07@202805 by

I am trying to control air flow with a butterfly valve operated by a hobby servo motor. The valve is 3" ID. The servo does not have quite enough umph to get the butterfly past 1/2 open.

If I were to switch to a 4" butterfly valve, would it be easier to open if the volume of air were the same as with the 3" valve? My guess would be that it would require the same force to operate the 4" valve. I hope I am wrong.

Thanks

John
----- Original Message -----
From: "John Pearson" <xeroCMC.NET>
To: "pic microcontroller discussion list" <PICLISTmitvma.mit.edu>
Sent: Thursday, July 07, 2005 8:26 PM
Subject: Physics question, air flow and valve...

{Quote hidden}

AFAIK flow on the one side of the disc of a butterfly valve attempts to push the
valve open while at the same time flow on the other side attempts to push it
closed. this makes the force needed to open or close it independant of flow,
however larger size of a valve does usually also means tighter seals, larger
seal surface so friction increases with size.

In my experience though there are huge differences with similar valves of
different manufacturers (who use different seal materials) you may have more
luck with another valve.

Peter van Hoof

John,

If it's a butterfly valve, the 4" wouldn't necessarily be easier to open
than a 3".  At least not due to the air pressure.
I recently designed and installed a motor driven ball valve, and just
cypher'ed the ratio needed for the power available vs. power req'd
to turn the valve.
I used a torque wrench to determine the force needed to move
the valves, calculated the ratio from the torque available from the
motor, and used chain driven sprockets at that ratio.  ( plus the
"fudge" margin )
The pressure applied to the butterfly valve is equal on both sides...
the side moving "away" from the pressure as well as "toward" the
pressure.
Figure a way to apply more leverage to the valve.  Mechanical advantage

Hope this helps,

D.
Good luck,
D.

{Quote hidden}

>
> >I am trying to control air flow with a butterfly valve operated by a
hobby
> >servo motor. The valve is 3" ID. The servo does not have quite enough
umph to
> >get the butterfly past 1/2 open.
> >
> > If I were to switch to a 4" butterfly valve, would it be easier to open
if the
> > volume of air were the same as with the 3" valve? My guess would be that
it
> > would require the same force to operate the 4" valve. I hope I am wrong.
> >
> > Thanks
> >
> > John

Why not just use a stronger servo? I haven't priced 4" butterfly valves
lately, but I know I can buy a 300 in-oz servo for less than \$40. I can't
imagine a new valve is a better option. (BTW, 'standard' servos are in the
40-50 in-oz range. There's a pretty big difference.)

-Denny

On 7/8/05, John Pearson <xerocmc.net> wrote:
> I am trying to control air flow with a butterfly valve operated by a hobby
> servo motor. The valve is 3" ID. The servo does not have quite enough umph
> to get the butterfly past 1/2 open.
>
> If I were to switch to a 4" butterfly valve, would it be easier to open if
> the volume of air were the same as with the 3" valve? My guess would be that
> it would require the same force to operate the 4" valve. I hope I am wrong.

How looks a butterfly valve ?

thx,
Vasile

>
> Thanks
>
> John
>
> --

Denny Esterline wrote:

{Quote hidden}

Or just buy another identical servo and reverse the pot and motor
wiring to get it to run backwards, then use them in tandem.

R

On Jul 7, 2005, at 5:26 PM, John Pearson wrote:

> I am trying to control air flow with a butterfly valve operated by a
> hobby servo motor. The valve is 3" ID. The servo does not have quite
> enough umph to get the butterfly past 1/2 open.
>
> If I were to switch to a 4" butterfly valve, would it be easier to
>  open if the volume of air were the same as with the 3" valve?

Surely it's easier to get a stronger "hobby servo motor" ?  Something
with more torque?
Check here: www.fatlion.com/sailplanes/servochart.html
Looks like a "standard servo" has about 40oz-in of torque, and you
can get get 275oz-in without too much trouble or expense.

BillW

On Fri, 8 Jul 2005, vasile surducan wrote:

>   How looks a butterfly valve ?

Like the air valve in a usual automobile carubrettor

Peter
On 7/8/05, Vitaliy <vitaliymaksimov.org> wrote:
> >   How looks a butterfly valve ?
> >
> > thx,
> > Vasile
>
> http://en.wikipedia.org/wiki/Butterfly_valve
>
> http://www.yourdictionary.com/images/ahd/jpg/A4butvlv.jpg

OK, saw these with other name, looks clear to me there will be no
important improvements in driving a 3" or a 4" diameter valve with the
same servo. Let me know if it's true.

best regards,
Vasile

> --

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