RE: Piping problem: Vacuum breaking remedy

From: <Steve>
Date: Thu Oct 31 2002 - 04:38:00 EST

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@yahoo.com] Sent: Thursday, October 31, 2002 7:20 PM To: PipingDesign@yahoogroups.com
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@yahoo.com> 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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Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/ Received on Thu Oct 31 04:38:00 2002