RE: !!! RE: about surge

From: <Erik>
Date: Sun Jan 23 2005 - 06:11:00 EST

Are you talking about a pumptrip or closing a valve at the end of the pipeline?
The response time of a pressure wave is 2l/a where L = pipelength and a= wavespeed.
The demping time is depending on the pipe roughness. In case of a pumptrip if the rotational inertia of the centrifugal pump and motor continue to rotate the pump for a while after power failure, water hammer pressure transients may be reduced.

Erik

Van: Firman Tuakia [mailto:engineer@lmbsp.ms.itb.ac.id] Verzonden: zaterdag 22 januari 2005 17:52 Aan: PipingDesign@yahoogroups.com
Onderwerp: !!! RE: [PipingDesign] about surge

anybody please help me: how to plot the oscillating head/pressure increase (when water hammer occur) at any point we want. especially how to:
1. calculate the frequency of the oscillation 2. estimating the damping tt causing the oscillated head/pressure become

     stabil again (such as the respon of step function)

Thanks before..
Regards,

Firman Tuakia

On Thu, 20 Jan 2005, Erik Scheir wrote:

>
> Measurement of Pressure.
>
> Lets keep it simple:
>
> Perfect vacuum cannot exist on the surface of the earth, but it
nevertheless
> makes a convenient datum for the measurement of pressure.
>
> Barometric pressure is the levelof atmospheric pressure above perfect
> vacuum.
>
> "Standard" atmospheric pressure is 1.0325 bar (19.6959 lbf/in2) or 760
> millimeters of mercury.
>
> Gauge pressure is measured above atmospheric pressure,while absolute
> pressure always refers to perfect cvacuum as a base.
>
> Vacuum is the depression of pressure below the atmospheric level.
Reference
> to vacuum conditions is often made byexpressing the absolute pressure in
> terms of the height of a column of mercury or of water.
>
> At least that's the way we define pressure in Europe.
> If it is still not clear, its always possible to graphically illustrate
the
> relationsship between gauge and absolute pressures.
>
> Erik
>
>
>
>
>
>
> _____
>
> Van: Steve McKenzie [mailto:mechproj@xtra.co.nz]
> Verzonden: woensdag 19 januari 2005 23:06
> Aan: PipingDesign@yahoogroups.com
> Onderwerp: RE: [PipingDesign] about surge
>
>
> Hi Al
>
> much as I enjoy deception, it was not used intentionally in this case.
> My Patm is 2bara being the sum of sealevel air pressure of 1bara plus
> the submergence of 10.2m or 1 bar. As you go deeper the pressure in the
> bell gets higher. It is my Pgauge that is -2. This condition could
> conveivably occur in a subsea line under water hammer conditions. Eriks
> contention is that you cannot go less that -1 barg while I maintain it
> depends what value you put on Patm.
> A bourdon tube pressure gauge measures the pressure differential between
> the inside and outside of the tube. With 2 bara on the outside and 0bara
> on the inside it would try to read -2, scale and mechanicals permitting.
> If you enclose an unconnected pressure gauge in a vacuum chamber, the
> needle should rise to about 1 bar, as there is no external pressure
> pushing the needle back to 0bar (must try this).
>
> The grey area it whether or not the pressure in the bell can be called
> Patm.
> Its easy to do in practical terms; just use a DP gauge with the HP leg
> disconnected and the LP leg to the pipe.
>
> I hope you remember to remove the vent plug when you install a pressure
> gauge, otherwise your Patm becomes the pressure inside the gauge casing
> instead of the surroundings. In hot places, with a well sealed case the
> difference could be considerable.
>
> Cheers
>
> Steve
>
>
> -----Original Message-----
> From: aluser2 [mailto:alwynk@shaw.ca]
> Sent: Thursday, January 20, 2005 8:15 AM
> To: PipingDesign@yahoogroups.com
> Cc: aluser2; mechproj@xtra.co.nz
> Subject: Re: [PipingDesign] about surge
>
>
>
> tsk tsk.
>
> math sleight of hand steve. U switched from local atmos pressure in
> absolute to saying it was the gauge reading (barg)
>
> "Gauge pressure is defined as Pabs - Patm = 0bara - 2bar(a)
> not= -2barg. not QED"
> ie your Patm is not -2barg.
>
> your gauge pressure is PAbs- Patm = 0bara- 2bara (as defined in your
> first
> line>ie. not 0barg-2barg)
> so the gauge pressure on the tube would be -2bara = -1barg
> (i'm in NA and years since i used bar , but i recall1 bar absolute is
> 101kpa=14.7psia. and 1bar gauge is 14.7psig (relative to atmos ie on top
> of earths 14.7pisa so (-2bara not -2barg). ie you wouldnt read this on a
> gauge.
>
> so the gauge would read -1bar (ie complete vacuum) (relative to the
> ambient bell pressure) which is possible as you say with a vacuum gauge.
> the riddle missed the sealed ends of the pipe which we assumed was what
> you meant.
>
> Practical problem - since a normal gauge measures relative to the
> surroundings you would have to be sure the gauge was able/calibrated to
> handle the bell submersed (environmental ambient pressure -32feet ). do
> i sense a troll? .
> ----- Original Message -----
> From: "Steve McKenzie" <mechproj@xtra.co.nz>
> To: <PipingDesign@yahoogroups.com>
> Sent: Tuesday, January 18, 2005 7:32 PM
> Subject: RE: [PipingDesign] about surge
>
>
>>
>> Hi Erik
>>
>> Local air atmospheric pressure inside air bell is P atm = 1 barg + 1
>> bara = 2 bara .
>> Pressure inside pipe is P abs = 0 bara.
>>
>> Gauge pressure is defined as Pabs - Patm = 0 - 2 = -2barg. QED.
>> However you will probably have to use a DP gauge to measure.
>>
>> I think most engineers can design a pipe (or a bell) which will stand
>> a vacuum by designing to stay below the critical buckling pressure.
>>
>> Either run the pipe through the sides of the air bell (sealed at the
>> intersections) or run the pipe up into and down out of the air bell,
>> or have the pipe sealed at both ends.
>>
>> We engineers can do anything!
>>
>> Cheers
>>
>> Steve
>>
>>
>>
>> -----Original Message-----
>> From: Erik Scheir [mailto:erik.scheir@pandora.be]
>> Sent: Tuesday, January 18, 2005 8:12 AM
>> To: PipingDesign@yahoogroups.com
>> Subject: RE: [PipingDesign] about surge
>>
>>
>>
>> If the pressure above the waterlevel is atmospheric, then the pressure
>
>> 10.3 m below the waterlevel is 1 barg (gauge) and an air bel with a
>> 100% vacuum will collapse.
>>
>> How can you run a pipe through an air bell?
>>
>> Cheers,
>>
>> Erik
>>
>>
>>
>> _____
>>
>> Van: Steve McKenzie [mailto:mechproj@xtra.co.nz]
>> Verzonden: zondag 16 januari 2005 19:46
>> Aan: PipingDesign@yahoogroups.com
>> Onderwerp: RE: [PipingDesign] about surge
>>
>>
>> I am normally not one to split hairs, but couldn't resist this one:
>> Consider an air bell 10.3m below water level, with a (perfect) vacuum
>
>> pipe passing through it. Inside the air bell is a pressure gauge
>> connected to the pipe. What is the gauge pressure?
>>
>> Cheers
>>
>> Steve
>> -----Original Message-----
>> From: Erik Scheir [mailto:erik.scheir@pandora.be]
>> Sent: Sunday, January 16, 2005 11:45 PM
>> To: PipingDesign@yahoogroups.com
>> Subject: RE: [PipingDesign] about surge
>>
>>
>>
>> I used this sofware perhaps even before you were born, but what has
>> that to do with te fact that -2 bar does nor exist on the earth. Try
>> to use Flowmaster its even better then impulse from AFT and you will
>> never see results with pressure nodes below 0 bar.
>>
>> Erik
>>
>>
>>
>>
>> _____
>>
>> Van: gautam wayse [mailto:captain_wayse@yahoo.co.in]
>> Verzonden: zaterdag 15 januari 2005 9:30
>> Aan: PipingDesign@yahoogroups.com
>> Onderwerp: RE: [PipingDesign] about surge
>>
>>
>>
>> hi
>> friend
>> better to go for impulse software for surge analysis
>> .from applied flow technology,.
>> use --- Erik Scheir <erik.scheir@pandora.be> wrote:
>>
>> ---------------------------------
>> What do you mean with - 2 bar? Is it barg?
>> The absolute vacum is - 1 barg or 0 bara, so - 2bar
>> doesn't exsist.
>>
>> erik
>>
>>
>>
>>
>>
>> -----Oorspronkelijk bericht-----
>> Van: Omid Hamlehdar [mailto:omid_7_ae@yahoo.com]
>> Verzonden: dinsdag 11 januari 2005 7:19
>> Aan: PipingDesign@yahoogroups.com
>> CC: mechproj@xtra.co.nz; erik.scheir@pandora.be
>> Onderwerp: [PipingDesign] about surge
>>
>>
>>
>> Hi all
>>
>>
>>
>> I have a project for water handling, a pipeline with
>> 100 km length, I am
>> studying about surge in it according to a probable
>> rapture in pipe and I am
>> going to close two valves surrounding rapture point to
>> avoid wasting water
>> and to find out about surge cause by closing valves.
>>
>> Any body has experience in this regards? How shall we
>> protect our system?
>>
>> I have heard from Erhard valve, they recommend a valve
>> called "pipe burst
>> control valve" to avoid wasting water when there is a rapture, this
>> valve will be closed in around 2 min and this will cause
>> surge in system, in some
>> point we have -2 bar minimum pressure. I know that you
>> may need to know
>> about the profile but generally I would like to know
>> how shall we suppress
>> this surge?
>>
>>
>>
>> Best regards
>>
>>
>>
>> Omid
>>
>>
>>
>> ---------------------------------
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>
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>
> =========================================
> PipingOffice - Excel Spreadsheets for Piping Calculations
> http://www.pipingoffice.us/
> =========================================
> Main site: http://www.pipingdesign.com
>
> Yahoo! Groups Links
>
>
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> http://www.pipingoffice.us/
> =========================================
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>
>
>
>
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>
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[Non-text portions of this message have been removed] Received on Sun Jan 23 06:11:00 2005

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