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LEV testing - layout changes
An LEV system is balanced for the layout it was designed around. Move a machine further from its hood, extend a duct to reach a new position, add a branch to serve another workstation - and that careful balance is disturbed. A system that was capturing perfectly can quietly stop working, not because anything broke, but because the layout it depended on has changed.
The short answer
An LEV system is designed and balanced for a specific layout: each hood positioned at its source, each duct sized to deliver the right airflow, the whole system balanced so every branch gets its share. Changing the workshop layout disturbs this. Moving a machine away from its hood cuts the capture velocity at the source; extending a duct adds resistance that reduces its airflow; adding a branch draws air away from the existing ones. None of this involves anything breaking - the system is intact - but the balance it depended on is gone, so it can quietly stop capturing effectively. That is why a layout change should trigger a re-examination.
An LEV is designed for a layout
An LEV system is not a generic appliance that works anywhere - it is engineered around a particular arrangement of processes and workstations. Each hood is positioned to capture a specific source, close enough to hold the capture velocity where the contaminant is released. Each length of ductwork is sized to carry the right amount of air from its hood to the fan. And in a system serving several points, the whole thing is balanced so that each branch draws its intended share of the airflow rather than the nearest hood taking it all. This design is specific to the layout it was built for.
That specificity is the point. The system works because the pieces are matched to their positions - the hood where the source is, the duct sized for its run, the branches balanced against each other. Change the positions and you change the conditions the design assumed. The system does not know the layout has moved; it goes on doing what its physical configuration dictates, which was tuned for the old arrangement. So when the layout changes, the careful match between the system and the workshop is broken, and the extraction can stop suiting the work it is meant to serve - without a single component failing.
Moving a machine
The most common layout change is moving a machine, and it is one of the most damaging to an LEV. The hood was positioned close to where the process was, because capture velocity falls off steeply with distance - so a hood only works if the source stays close to it. Move the machine away from its hood, even by a modest amount, and the source is now further from the point where the capture velocity is adequate. Because the velocity falls so steeply with distance, a machine shifted a foot or two from its hood can find itself in air the hood barely reaches.
The result is capture failure at that point, even though the hood, duct and fan are all working perfectly. The extraction is still running and still pulling air at the hood - but the source is no longer in the effective capture zone, so the contaminant escapes into the room instead of being drawn in. This is a genuinely invisible failure: nothing looks wrong, the system runs as before, but a machine that was covered no longer is, simply because it moved. Anyone rearranging a workshop to make space or improve flow can unknowingly move a process out from under its extraction, and unless someone re-checks, the loss of capture goes unnoticed.
Extending ducts and adding branches
Two other common changes disturb the balance in a different way. Extending a duct - to reach a machine in a new position, or to route around an obstruction - adds length, and length adds resistance to airflow. The fan can only produce so much pressure, so a longer, more resistant duct delivers less airflow to its hood than the shorter original did. The hood may then fall below the airflow it needs, losing capture, even though nothing has broken - the extra resistance has simply eaten into the airflow the design allowed for.
Adding a branch is the other classic disturbance. A system balanced to feed a set number of hoods has its airflow shared among them by design. Add a new branch and hood to serve another workstation, and that new branch draws air from the same fan - reducing the airflow available to all the existing branches. Every hood on the system can lose a share of its capture to the newcomer, so a single addition can quietly weaken the whole system. This is why you cannot simply bolt on extraction for a new machine and assume the rest is unaffected: the system is a shared, balanced whole, and adding to it takes from what was there. Both changes leave every component intact while undermining the performance the balance provided.
Why a layout change means a re-test
Because layout changes break an LEV silently - no component fails, the system runs as before, but the capture is compromised - a change to the workshop layout should trigger a fresh look at the extraction. Moving a machine, extending a duct, adding a branch, or rearranging the floor are all reasons to re-examine whether the system still captures effectively in the new arrangement. A thorough examination measures the airflow and capture velocity at each hood and confirms whether the balance still holds, or whether the change has pushed a hood below what it needs.
This matters because the assumption that extraction keeps working after a layout change is exactly the trap. The system looks unchanged and runs unchanged, so it is easy to assume it still works - but the thing it depended on, the layout, has moved. The scheduled thorough examination will catch this eventually, but a significant layout change is a reason not to wait for the next scheduled test, because the loss of capture starts the moment the layout moves. Treating a layout change as a trigger for re-checking the LEV - rather than assuming it is unaffected - is how you avoid running a broken-but-intact system unaware. The rule of thumb is simple: change the layout, re-check the extraction.
The takeaway
An LEV system is balanced for the layout it was designed around - each hood at its source, each duct sized for its run, the branches balanced against each other. Change that layout and you disturb the balance: moving a machine takes the source out of the hood's effective capture zone, extending a duct adds resistance that cuts its airflow, and adding a branch draws air away from every existing hood. In each case nothing breaks, yet the capture is compromised.
That is what makes layout changes so treacherous - they break the system silently, leaving it running and looking exactly as before while it quietly stops capturing. So a significant layout change should trigger a fresh examination rather than an assumption that the extraction is unaffected. A thorough examination measures the airflow and capture velocity at each hood and confirms whether the balance still holds in the new arrangement. Change the layout, re-check the LEV - because the system depends on a layout that no longer exists.
Questions
Yes. An LEV is balanced for a specific layout - hoods at their sources, ducts sized for their runs, branches balanced against each other. Moving machines, extending ducts or adding branches disturbs that balance and can compromise capture, even though no component has broken and the system runs as before.
Because capture velocity falls off steeply with distance, and the hood was positioned close to where the source was. Move the machine away from its hood, even modestly, and the source leaves the effective capture zone - so the contaminant escapes instead of being drawn in, while the system still runs and looks fine.
Length adds resistance to airflow. The fan can only produce so much pressure, so a longer, more resistant duct delivers less airflow to its hood than the shorter original did. The hood may then fall below the airflow it needs and lose capture - the extra resistance eating into the airflow the design allowed for.
Because a system is balanced to feed a set number of hoods, sharing the fan's airflow among them. Adding a branch draws air from the same fan, reducing the airflow to every existing branch. A single addition can quietly weaken the whole system, so you cannot bolt on extraction and assume the rest is unaffected.
No - that is the danger. No component fails, so the system runs and looks exactly as before, while the capture is quietly compromised. A machine that was covered no longer is, or every hood loses a share of its airflow, with nothing to signal it. The failure is real but invisible.
Yes. Because layout changes break an LEV silently, a significant change - moving a machine, extending a duct, adding a branch, rearranging the floor - is a reason to re-examine the extraction rather than wait for the next scheduled test. Change the layout, re-check the LEV.
Rearranged your workshop, moved a machine or added a branch? Our thorough examination confirms whether your LEV still captures effectively in the new layout - or whether the change has quietly broken the balance.
