Steve,
You may well be right but until you look at the system how do you know?
If the system is working at full flow and there is power trip there will likely be a negative pressure wave followed by an uncontrolled high pressure spike. The negative pressure wave could be sufficient to collapse the pipe. The resultant high pressure will most likely contained in the pipe. The physical properties of carbon steel under high strain rates being improved (Piping Design-Kellogg).
It is a disrict coling scheme with many users. However a pressure spike would cause noise to users. If a sub header was to fail anbd a building went off line the owner would not be a happy Vegemite. The risks have to be eveluated. Likelihood and consequences. If the consequence is loss of cooling water to a shopping centre, loss of trade and foodstuffs spoiling you are in dire straits.
The point I make is that without using the tools available to evaluate something your "knowledge is meagre and unsatisfactory" Lord Kelvin.
Geoff
Steve McKenzie <Mechproj@xtra.co.nz> wrote:
Hi Robin
Have you changed lifestyle?
I am about to need some help on dust suppression.
Have you done anything in this regard?
This is for Kens digestion and Geoffs indigestion.
Geoff will cane me for this, but for water supply I seldom worry about
surge protection at concept phase other than to throw 15% on the design
pressure and 10 - 20% on pumping station costings. The iterative nature
of design normally requires an estimate to be made on secondart issues.
Surge is a secondary effect and can only be evaluated after the primary
system is laid out. Surge anticipators are good on a force mains, but
most (true) networks have so much frictional diffusion and capacitance
that they never reflect anything much. This aint the case with force
mains which can blow your head off.
With a truly closed system, and I have never done a closed network
(assume its district heating/cooling), things will change a little but
diffusion and unequal conduit lengths should tend to stop things getting
out of hand. Also with a network, the serious events are supply (pump)
generated and the likelihood of a widespread (valves closing
simultaneously) flow rejection is normally impossible.
Experience with previous open circuit projects suggests to me that you
may need some air vessels at each pump station at preliminary costing
stage, and these will be dropped off as the surge model matures. If the
system is a district heating or cooling system then you will need some
volume compensation capability anyway so the surge vessels may double as
pressure accumulators for volume change; thus reducing cost.
My gut feel is that if there are heaps of small demand users, no major
elevation changes and no long force mains (pressure pipes with no active
branches) then eventual provisions for water hammer will be bugger all,
and water hammer will be relegated to a secondary issue.
It pays to remember that the majority of major liquid distribution networks were commissioned prior to the proliferation of water hammer software, and most operate acceptably with regard to transients.
Cheers
Steve
-----Original Message-----
From: <a href="/group/PipingDesign/post?postID=U5QfdGjeum-fDuTso9mvQWEyOIkQPagX51FwMqXy_NWCfu7evGKXAyO8nNtNksn_J2EnPxv4ZySr59eOSAR10ViO5naG3aQ">PipingDesign@yahoogroups.com</a> [mailto:<a href="/group/PipingDesign/post?postID=U5QfdGjeum-fDuTso9mvQWEyOIkQPagX51FwMqXy_NWCfu7evGKXAyO8nNtNksn_J2EnPxv4ZySr59eOSAR10ViO5naG3aQ">PipingDesign@yahoogroups.com</a>]
On Behalf Of Robin Badcock
Sent: Friday, January 13, 2006 11:03 PM
To: <a href="/group/PipingDesign/post?postID=U5QfdGjeum-fDuTso9mvQWEyOIkQPagX51FwMqXy_NWCfu7evGKXAyO8nNtNksn_J2EnPxv4ZySr59eOSAR10ViO5naG3aQ">PipingDesign@yahoogroups.com</a>
Subject: Re: [PipingDesign] Surge and Water Hammer
Ken,
As an added safety feature of the piping network will there be surge anticipation valves fitted.
Cheers,
Robin Badcock
Irrigation Design Consultant
Badcock Irrigation Services
4154 Meander Valley Road
Deloraine, Tas. Australia. 7304
Ph. 03 63623003
Fax. 03 63622977
Sent: Friday, January 13, 2006 10:02 AM
Subject: [PipingDesign] Surge and Water Hammer
> This mostly directed at Geoff but all advice is welcomed,
>
> We have a large closed network utilising insulated steel pipe and I am
> trying to understand the likelihood or risk associated with a pressure
> surge.
>
> This network is entirely buried and we have not been commissioned to
> undertake the pumping plant design- so we have little control of valve
> selection and/or control within the plants.
>
> There will be 3 pumping stations each pump is variable flow and all
> valves in the network are manually operated large diameter butterfly
> valves. Roughly there will be 20 pumps in each pumping station.
>
> My limited understanding of surge and water hammer is that it relies
> on a fast change in pressure (by valve closure or loss of pumps etc)
> in the network which propogates through out the system causing if not
> catastrophic failure then fatigue.
>
> The overall system pressure will modulate in accordance with demand
> but this will be controlled by VSD's on the pumps, also given that the
> entire network is completely restrained by the soil and that there is
> no real risk that a valve can be shut quickly...Is surge and water
> hammer still a potential risk on the system and why?
>
> The size of the network dictates that any ramping up or down of pumps
> will not induce a rapid change in the network pressure. And even if
> one pumping station goes down because of power failure the other two
> will be designed to pick up the slack. My thoughts are that this still
> may induce a rapid change in pressure??
>
> Can managing the operation (including the event of a failure) of the
> network in such a way as to avoid any rapid pressure variations be
> used to eliminate the risk or surge and water hammer?
>
> Any ideas or comments??
>
>
>
>
>
>
>
>
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>
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