Rank: Forum user 
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I have just tested the LEV in the welding area of the workshop with a digital hot wire amometer and got the reading in metres per second (8.6 at the hood). I cannot find the original documentation for the extractor so am trying to find an actual figure that is deemed to be suitable & sufficient. This particular LEV seems to extract the welding fume efficiently when I observed it so there doesn't seem to be an issue but I cannot find an actual measurement that it should be reaching to be classed as suitable. I have read through most of the LEV related docs from the HSE but cannot seem to find what I am looking for. Also I have not read anything other that the test should be done at the hood................again no exact measurements away from the hood to do the flow test so I am presuming it is level with the hood?? I am also in the process of selecting LEV for a new workshop and in some of the specs on the documentation, the max airflow at the hood in m3/h is documented at 1050 which on a conversion is 233.49 metres per second so by this yardstick my tested LEV seems to fall short......................
Any input appreciated. Thanks.
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Rank: Super forum user
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Adrian:
I suggest you check the sums? It would seem you have dropped a decimal or compared seconds with hours... 233.49 ms-1 - is 840km per hour which is close on supersonic. I am willing to wager that this is not correct?
Hood face velocity (is it an 'elephant trunk hood or a fixed hood?) will not always correlate with capture velocity at the actual point of work - it depends on hood design , distance from the work piece and (to a very large extent) the nature of the work room general ventilation and etc etc.
Happy to advise if you wanna post dimensions etc.
Steve...
Steve
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Rank: Forum user
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steve e ashton wrote:Adrian:
I suggest you check the sums? It would seem you have dropped a decimal or compared seconds with hours... 233.49 ms-1 - is 840km per hour which is close on supersonic. I am willing to wager that this is not correct?
Hood face velocity (is it an 'elephant trunk hood or a fixed hood?) will not always correlate with capture velocity at the actual point of work - it depends on hood design , distance from the work piece and (to a very large extent) the nature of the work room general ventilation and etc etc.
Happy to advise if you wanna post dimensions etc.
Steve...
Steve Thanks for your reply. I just went back to the conversion site I used (http://www.calculatoredge.com/optical%20engg/air%20flow.htm) and I had not filled in a box re radius of circular ducting (was left at a default of 2"). My 8.6 metres per second is now converting to 2259 m3/hour!! The hood is a slightly curved plate (14"x12") with the fan aperture within the plate measuring 7"x6". The plate is at the end of an articulated elephants trunk which then connects to some 6" ducting which goes outside. Given this info where would you do a flow test with a digital hot wire amometer? Thanks.
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Rank: Super forum user
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Its difficult to offer short answer in a forum like this - there are so many variables but...
A 'normal' welding operation (not grinding or sawing... - where the fume and vapour is released relatively gently into air which has little turbulence - then a hood which is pulling 1-1.5 ms-1 hood face velocity is likely to be all you require to control the fume PROVIDED the hood is positioned as CLOSE to the work piece as practicable to pull air AWAY from the operator (and slightly above to take advantage of thermal convection). More than this is liable to be wasting energy. to no practical effect.
The reason for doing LEV testing is mainly to check that design performance parameters are maintained. Do you have a record of the original design spec and pump capacities? It's not normally necessary to measure with enormous precision - you are trying to work out if the system has tried to ingest a couple of paper towels or is suffering severe constrictions due to dust deposits...
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Rank: Super forum user
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Rank: Forum user
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steve e ashton wrote:Its difficult to offer short answer in a forum like this - there are so many variables but...
A 'normal' welding operation (not grinding or sawing... - where the fume and vapour is released relatively gently into air which has little turbulence - then a hood which is pulling 1-1.5 ms-1 hood face velocity is likely to be all you require to control the fume PROVIDED the hood is positioned as CLOSE to the work piece as practicable to pull air AWAY from the operator (and slightly above to take advantage of thermal convection). More than this is liable to be wasting energy. to no practical effect.
The reason for doing LEV testing is mainly to check that design performance parameters are maintained. Do you have a record of the original design spec and pump capacities? It's not normally necessary to measure with enormous precision - you are trying to work out if the system has tried to ingest a couple of paper towels or is suffering severe constrictions due to dust deposits... This particular LEV has been in place for 4 years. I took over the H&S role 12 months ago and have realised there have been no previous documented flow tests done. There is also no documentation for the equipment to look at original specs but now I have taken a reading and compared to specs of similar equipment I am happy that the pull is more than sufficient for the task for which it is being used so will use this measurement as my baseline going forward to check for efficiency reductions. Once I have put the report together in a suitable format (I have looked at a few examples) then I think that is as much as I can do. Thanks.
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Rank: Forum user
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This would be a luxury and something I may put forward when we move premise shortly but I believe the LEV in question is suitable & sufficient for the operation. My concerns were initially with the flow rate conversion (my error!!) and the seemingly lack of detail in regard to the positioning of the measuring equipment for measuring flow. Thanks.
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Rank: Super forum user
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Rank: Forum user
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Thanks all for your input on this matter, much appreciated.
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Rank: Forum user
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Agree with previous comments, your maths seems astray.
Have you checked your 'units', you seem to be switching both SI and Imperial units.
Suggest you use just SI units
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