With fume extraction welding, the effectiveness of the smoke capture is always dependent on the strength of the fume extraction system. No matter how effective the torch or skilled the welder, without a system strong enough to capture the smoke, both the welder and the environment will not be spared from the harmful effects of metallic fumes.
To achieve the optimal effectiveness of your fume extraction system, you have to know what to measure in the system, where to measure, and what are the baselines you need to be certain your system is up for the task. So with that, let's walk through testing your fume extraction system!
The two main parameters to test on a fume extraction system are the vacuum's static pressure and flow. To simplify this step, and because they are dependent of each other in the case of smoke extraction using a MIG torch, static pressure can be the only required measurement. Static pressure is measured using a standard gauge.
Static pressure is recorded using different units of measurement; in the United States, for instance, static pressure is measured in inches of water column, or "w.c". This literally translates in a practical sense to how hard the vacuum is pulling on water. Outside the United States, static pressure is generally measured via Kilopascal, or kPa.
There is no simple answer to the question of how much static pressure or flow one needs. The amount of static pressure - and hence flow - that you need will always be relative to the parameters that you are welding at, not to mention the weld position, filler material, etc. If you are welding, for instance, flux core wire at low parameters, you don't need an extreme amount of static pressure or flow to suck in the smoke.
The more the welding parameters are raised, the more smoke will be produced, and thus the higher the amount of static pressure will be needed. For example, if you are welding on .045 flux core wire at 240 amp welding on a flat surface, you'll be looking to achieve around 60 inches of static pressure (60 w.c.) right before the torch to properly extract smoke.
The baseline static pressure for any fume extraction system should be 50 w.c. right before the torch. If your system cannot achieve that level of static pressure, it may not produce enough suction for the welders to adequately capture smoke depending on the metal, thickness gauge, etc.
With different positions less conducive to smoke extraction, or if you're welding with higher parameters more in the 300 to 350 amp range using a hot gas mix, the static pressure has to reach between 80 and 90 w.c. right before the gun (at the elbow) in order to effectively extract the smoke.
In order to achieve the best result for fume extraction, you need both a high static pressure and a high rate of flow from the fume extraction unit going through the torch. Most of the time when the results are not optimal for the welding staff, the reasons are because of either pressure drop in the system - where you don't have the high static pressure being maintained, or there is restriction on the flow, where the flow of the fume extraction torch is choked at some point, blocking the passage of metallic particles to the system from the torch.
The filter on portable systems is a common culprit for losses in static pressure and flow. Consider the filter as one barrier for the flow. If the air filter is full of metallic particulates, then it will be compacted by the pressure, which will then make it harder for the air to go through, which will cause not only the internal static pressure of the vacuum will rise, but the flow to drop considerably. Both static pressure and flow need to be at a proper level for the entire fume extraction system to work at it's best, and a drop in either will lessen the effectiveness of both.
So how does one go about testing a fume extraction system? In practice, testing for flow is a complicated test and doing so in a laboratory setup is the best (and really only) method for determining a relevant, accurate result. For static pressure, the method is more easily done in an industrial setting. The key is the location: where you test for static pressure matters. For fume extraction systems, the hose connect at the entrance of the torch is the optimal testing location. This would be at the elbow of the fume extraction torch where the particles funnel into the fume extraction system.
Know that when test for static pressure the torch is a constant in the problem. If the static pressure is a known quantity, then the flow is a known quantity as well. There is a direct relation from one parameter to the other. The way to measure the static pressure in your fume extraction system is to add a piece of hose and plug the vacuum gauge while replugging the torch. It is critical that air travels through the torch into the elbow and finally to the extraction system for an accurate static pressure reading.
Measuring static pressure without the torch will give you a number that isn't relevant to your operation, because without the torch connected it cannot be determined what the static pressure of the vacuum system is going to be. In short, measuring the system without the torch will tell you what the maximum static pressure of the system is, but not the applied static pressure when it's being used in an industrial application - such as when it's connected to an active fume extraction torch. It's really important to connect the torch and do a reading with the vacuum going through the torch. Having a welder welding with the torch doesn't change the information because the welding won't affect the static pressure in any way - only having the vacuum connected to the torch when performing the measurement.
Another variable and important measurement to verify is the static pressure if there are multiple welders using the same station - such as a multi-unit vacuum system or a centralized vacuum system. To do this you must measure and check the gauge over a period of time to ensure there isn't any dropping in static pressure when multiple torches are connected to the system. Ideally, you want the pressure to be as stable as possible at the entrance of the torch - i.e., the elbow connect.
Besides testing the unit with multiple torches (if it can be supported), it's always wise to measure every torch with the system individually assuming that the fume extraction vacuum is providing a constant level of static pressure. Connect each torch one at a time, get their pressure reading, and if any is out of line with the base line read out, starting working up the torch cable to check for leaks or obstructions like flexible hose clamps. With those steps taken you should be able to achieve the results you're looking for out of your fume extraction system, but you need to read and check the parameters for each torch on the fume extraction system. In an industrial setting, leaks or weak points can happen anywhere - it could be a leak right before the torch causing the issue.
Whether testing multiple torch units or a single unit, where you should test is the same no matter what, and that is testing right before the elbow of the torch. If you don't get a good reading from the elbow location, the first troubleshooting step is to check for static pressure at the inlet of the fume extraction system. It is here where you'll know instantly if there is an obstruction in the torch or if it is the system itself that needs to be looked at more closely. A static pressure reading higher than that of the reading of the elbow means the torch has a leak or an obstruction; if it's the same or lower, the issue is within the fume extraction system.
Should static pressure again be lower than an acceptable baseline at the inlet, then move to the blower of the vacuum system to make sure that it is dispensing the right amount of static pressure. The key to working upstream on your fume extraction system is that you want to see which components have an obstruction (if any) to determine what that obstruction may be, and remove or repair it.
Whenever a new component is added to the vacuum system, a drop in static pressure is to be expected, which means a drop in flow is also to be expected. Measuring right before the torch at the elbow will tell you the reality of the fume extraction system's static pressure and confirm to you the amount of pressure that's available at the torch. You have flexible hoses, you have leaks, and all sorts of possible obstructions in the torch cable and the vacuum hose, but that static pressure at the elbow is the measurement that matters, because by knowing that you can fix or replace the problem areas upstream - such as by covering leaks, using bigger hoses, or even shortening cables - should the second test at the inlet prove the system's static pressure is fine.
Contorting the torch cable as it might be in a difficult welding position is not necessary when doing the gauge measurements. To get a true reading, ensure the fume torch shroud is unobstructed and the torch cable isn't bent in an unnatural way.
Every application may require a different vacuum level, but what's universally true and must be noted is that the more static pressure you have available the better result you will get from your smoke extraction. A more powerful vacuum will allow the torch to overcome pressure losses from hose leaks, long cable, small obstructions, etc. to allow for the best fume extraction welding operation possible.
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