[K3CAL] Regarding the PVC used in the antenna launcher

[David Weaver]

HI ALL
ALSO the Launcher has an air pressure relief valve on it set at 125LBS
Dave
-----Original Message-----
From: k3cal-bounces at mailman.qth.net [mailto:k3cal-bounces at mailman.qth.net]
On Behalf Of Edwin A Noell Jr
Sent: Saturday, September 21, 2013 9:39 AM
To: Calvert Amateur Radio Association - K3CAL
Subject: Re: [K3CAL] Regarding the PVC used in the antenna launcher

Dennis;

See the attached PDF file for the specs for SDR21.  The working pressure for
the SDR21 is 200 psi.  The maximum bursting pressure, found elsewhere on the
website, is 630 psi.

And I do understand the temperature differential. But 200 psi derated by 20%
is still 160 psi. Even at 110 degrees, the derating factor is still only
50%, which gives a working pressure of 100 PSI. Again this is well above the
pressures used in the launcher, and way, way under the bursting pressure of
630 psi.

On the spec sheet, I also see the warning about using the PVC for compressed
air. But in the many technical manuals I've searched, I have never found any
reasons for this. They just say "don't do it".

However, practical experience has shown that for the temporary storage of
air at the pressures needed for launching tennis balls, golf balls and
potatoes, sdr schedule pipe is quite adequate for the job.

It all boils down to the caveat that if you don't do anything stupid, you
won't get hurt.

And personally, if my launcher is 110 degrees, I'm not going to be be
filling it to 200 psi and trying to launch a potato 600 feet in the air.

Ed


On 09/21/2013 07:31 AM, N3QHC wrote:
> Hi Ed,
>
> Not sure of your source of 200 psi.  If from the people that makes 
> these launcher's then I would be concerned.  I might be stated as such 
> for promotional purposes.  I rather rely on engineering specs.  Having 
> a device explode next to one's body is not going to have very good
results!
>
>   There are other factors that determine if PVC is 'good' at a certain 
> pressure such as TEMPERATURE.  See 
> http://www.engineeringtoolbox.com/pvc-cpvc-pipes-pressures-d_796.html .
> Notice max pressure for PVC is 166 psi but at 73-d F the pressure is 
> reduced by 20% or 132 psi.  Consider having a launcher in a hot car 
> during the summer and getting it out to launch a tennis ball.  The max 
> pressure is .3 x
> 166 psi at 130-d F or about 60 psi max.  Source:
> http://www.engineeringtoolbox.com/thermoplastic-pipes-temperature-stre
> ngth-d
> _794.html
>
> Notice that CPVC has higher max psi than PVC.  This why PVC is illegal 
> to use in house plumbing for hot water.  CPVC is legal for hot water 
> plumbing in homes.
>
> Just because someone makes these launchers does not make them safe to use.
>
> 73, Dennis N3QHC
>
> -----Original Message-----
> From: k3cal-bounces at mailman.qth.net 
> [mailto:k3cal-bounces at mailman.qth.net]
> On Behalf Of Edwin A Noell Jr
> Sent: Friday, September 20, 2013 10:42 PM
> To: Calvert Amateur Radio Association - K3CAL
> Subject: [K3CAL] Regarding the PVC used in the antenna launcher
>
> Guys:
>
> If you read the specifications on the antenna launcher, you'll find 
> that the launcher is made with SDR21 PVC.
>
> This PVC is good for a pressure of 200 psi, which is well beyond the 
> working pressures of 70-80 psi used in the launcher.
>
> However, thank you for the warning.
>
> Ed, KC3AEN
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