Hi Robin
from your burst of excellent and detailed responses to queries, it appears you have some time on your hands.
My question#1 is when does your boss get back from his vacation?
Question #2, I have to bang a magflow into an existing line and intend using the 2/3 upstream, 1/3 downstream that I normally use. Trouble is that I wont have my normal minimum 10D up and 5D down probably more like 5D up and 2.5D down, closer to your numbers. The disturbances at each end are 1.5D bends, same plane. Line size is probably 150NB and flow rate around 170m^3/h, water. The metering is for process control, not accounting, so accuracy isnt hellish important but it would be comforting to know the expected accuracy. Have you or anyone else seen any data on the effect on accuracy when departing from "the rule"? I expect a slightly higher reading than actual at higher flow rates (due to spin), but someone has surely done a bit of research on this. Am up to my ears in rules of thumb and would prefer a bit of supporting research data. Have perused ISO5167, but it doesn't really apply to an induction driven meter.
Personally, I feel this question may take a couple of hours of digging
to find the answer, which I am sure would be of use to a number of list
members. I suggest that any member who makes a "crime" against this
group be "fined" by being required to provide a well-researched and
referenced (1 page minimum) response to a nominated question, such as
this (question #2, or course), within one week.
It would improve the knowledge base of this group, and reset the clock.
Paul could judge if such a crime has occurred. He would like it as he
likes throwing his weight around.
Whaddayathink?
Cheers
Steve
-----Original Message-----
From: Robin Badcock [mailto:rbadcock@vision.net.au]
Sent: Thursday, February 17, 2005 1:57 PM
To: PipingDesign@yahoogroups.com
Subject: Re: [PipingDesign] querry....
Vaibhav,
There exists numerous distances for devices that are inserted within the pipeline and these vary somewhat to the duty they are to perform, i.e. paddle switches may have a requirement of 5 times pipe diameter of straight pipe up-stream and down-stream from the point of installation. Sensitive propeller type instruments may call for 10 times pipe diameter. Generally speaking the manufacturer will provide you with guidelines on the correct installation. These guidelines are in the interest of having the device operate, and achieve the base line accuracy that the maker claims on their literature.
This does not answer your question fully. The reason for the straight pipe sections is for the reduction of possible turbulent flow that may affect the devices operation.
In answer to you query on the straight pipe sections associated with check valves, we have witnessed first hand non return valve mechanical failure due to excessive turbulence when installed too close to the down stream side of a pressure sustaining valve. The end result was total internal valve failure within two years. This less than ideal installation was due to space constraints. One solution was to install a more robust valve and be prepared to live with the extra maintenance. The correct solution would have been to observe a greater distance of straight pipe work, down stream of the sustaining valve, if space would have permitted.
If you goggle pipeline turbulence you may turn up some useful info. Perhaps Paul has a link or some information on the Piping Design web page.
The orifice plate that you may be manufacturing yourself for head loss/flow regulation will also be subject to straight piping requirements for the same reason of attaining reliable and repeatable regulation. If installed into a turbulent pipeline area variations may well exist. Software is available from the likes of Dorot, Bermad and quite likely other control valve manufactures and although I have not checked, software and information is likely to be freely available on this subject. This was certainly the case some years ago.
I hope that this helps.
Cheers for now.
Robin Badcock
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> Can any one please tell the required straight upstream and downstream
> requirement for Restriction Orifice? Please note that this orifice is
> only for pressure drop purpose and not for flow measurement. What
> could be the reason for this requirement?
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> Has anyone come across the straight length requirement for check
> valves, especially swing check valves? Why is this needed?
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> Request members to throw some light on this.
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> Regards
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> Vaibhav Devdhar
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Yahoo! Groups Links Received on Thu Feb 17 04:11:00 2005
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