Oops - first sentence should read ....under a certain SDR......
with SDR as the number gets larger, the pipe gets weaker.
Sorry bout that chief.
Steve
- In PipingDesign@y..., "Steve McKenzie" <Mechproj@x> wrote:
> If PE pipe is over a certain SDR (Standard Dimension Ratio or Mean
O.D.
> divided by wall thickness) then it will withstand a full vacuum
even if it
> is unsupported.
> At 20 Deg C, if your SDR is 17 or less, the pipe will stand a full
vacuum
> for at least 12 hours, including a safety factor of at least 2.5.
At higher
> temperatures the rating will decrease owing to reduction of the
> circumferential bending modulus. For 50 years life at 20 deg C
under full
> vacuum the SDR should be not more than 13.6. Many higher pressure
lines will
> stand a full vacuum because the wall thickness to withstand normal
operating
> pressure is sufficently large.
>
> Have fun.
>
> Cheers
>
> Steve Mckenzie
>
>
> -----Original Message-----
> From: Gang Cvg [mailto:cvg_gang@y...]
> Sent: Thursday, October 31, 2002 7:20 PM
> To: PipingDesign@y...
> Subject: Re: [PipingDesign] Piping problem: Vacuum breaking remedy
>
>
> Dear David,
> As you have been warned about the possible vacuum
> formation, which seems to be quite genuine, I think
> you have to look for some solution of istalling an (or
> more in number with stand-by philosophy) automatic
> vacuum breaking valve similar to the ones used on tank
> tops.
> In the event of building up of such a vacuum, it will
> open up and let in the atmospheric air to fill the
> space emptied by the receding water. During its normal
> intended duty it wil close the port to prevent any
> loss of water to the atmosphere. Keep the stand-by one
> always well tuned. Please give a thought to it. You
> might get still better solutions. Good luck!!
> C. V. Gangadharan.
> --- Wilkonet <wilkonet@y...> wrote:
> > Hi Everyone,
> >
> > I've recently started my first main job as a trainee
> > mechanical
> > engineer. One of the first problems ive came across
> > is to modify a
> > piping system for supply water to a power plant. The
> > material is
> > hdpe, 450mm dia, 7400m long. The is currently
> > insufficient flow so a
> > modification is needed. My modification means that
> > the change in
> > elevation from pump to dam is now -8m instead of
> > previously 8m. (the
> > pipe would be re ruited)This in theory would give
> > suffiecent flow.
> > However I have been warned that if the pump is
> > turned off this could
> > cause a vaccuum to be formed and the pipeline to be
> > crushed.
> >
> > I have been searching through the net to try and
> > find some
> > information on designing pipe systems but have
> > failed to find
> > anything to give me information on a system which
> > pumps 'down hill'.
> >
> > It would be great if anybody could give me some
> > advice or any
> > information which would halp me in my problem.
> >
> > Regards,
> >
> > David Wilkinson
> >
> >
>
>
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Received on Thu Oct 31 05:52:00 2002