Large Shop Dust Collector - Advice Please

[William Dameron]

I am trying to decide between three dust collection routes for the community shop I am in the middle of opening here in Las Vegas.

1) A large external baghouse
2) 4 Laguna 3hp cyclone units, outside the shop, under cover
3) 4 Laguna 3hp cyclone units, inside the shop

The back story is this: When I started the process of opening this business, a couple years ago, I tried to do my due diligence, which included talking to the county fire department. Together, we decided on acceptable dust collectors - Laguna tools 3hp units. 4 of them, wich gives me over 8000cfm total. I potentially need this much, because as a community shop, I will have many people working at one time. These collectors are quiet, as far as dust collectors go, and filter very well. Additionaly, by locating them inside, near the tools, I can get away with doing the plumbing myself, rather than hiring a contractor, which is expensive, or worse yet, a dust collection engineering firm, which is crazy expensive. I got a good deal from Laguna, and ordered them.

The real pain is that since talking to the fire department, many months ago, they have since come up with a new regulation: any dust collectors INSIDE a building must have a sensor installed, which will shut the collector off if the filter gets torn, removed while running, or if someone tries to start it without the filter. Ugh. I called Laguna, and they do not have this built in to any of their units, or a recomended method of installing such a sensor. So, to do that, I have to figure out how to modify them myself.

So now I have to re-evaulate everything, and decide what to do and to that end, I need help with the following questions:

1) Does anyone know how to modify the dust collectors to auto shut off when needed? Ie a magnahelic gauge, bag rip detector, or something like that?
2) If I choose a big external baghouse (1 is coming up for auction near me), or park the Laguna units outside, will it hurt my climate inside? I am worried because it gets stupid hot here in the summer, and if I suck all my cold air and exhaust it outside, my customers may not find the place so enjoyable... I have swampers for the warehouse, so I guess any air being drawn into the building is at least being drawn across the swampers.
3) How is the maintenance on baghouses? I know very little about these suckers (ha, no pun intended...)

And in general, what is everyone's advice?

[Anthony Whitesell]

You have already checked with Laguna. How about the other manufacturers? Is there something you can retrofit from someone else into the Laguna DC you already have?

Being an electronics guy, I can envision how you could roll your own. On that note, you have two different issues to detect. Detecting if the filter is not attached is easy, just a switch to detect the clamp/filter is on and in series with the start button. Detecting a tear would be a loss of back pressure, so you would need a magnahelic gauge with an electronic output. Either analog that could be be used to trigger an alarm or shut the machine down. Or a contact output where the sensing is internal, and the output is a relay that allows the machine to run or shutdown (ie., both parts of option #1 combined).

[William Dameron]

So far I haven't called other manufacturers, but have been searching the internet. I have found baghouse 'rip detectors', and similar things, but so far everything I have found sets off an alarm, or just gives input to a gauge - no output wire to shut off a relay or anything. But, it definitely could be out there - and some of the product I have found might be able to trigger a relay, instead of an alarm, ec. I definitely havent' found a bot on option yet.

As for detecting the filter being missing, like you said, that's easy - a switch similar to what's found on a fridge door, washing machine lid, etc. etc. etc. But, I also figured that a pressure differential gauge would accomplish the same thing, because obviously having no filter attached would read 0 pressure differential ie the mother of all rips. So, if you can accomplish the second objective, I think the first one would be handled.

I really don't mind the idea of parking them outside - it saves me space and noise inside the shop. It just presents other complications, like possibly having to pay someone to run ducting, and dealing with the landlord and getting permission to have an exteran unit(s). Ugh, don't know what to do.

[Anthony Whitesell]

The problem with using the magnahelic to detect the lack of a (eg., not installed) filter is the DC must spin up in order to detect the lack of pressure.

I think any aftermarket solution will be half bolt-on. As the products you found may be able to trigger a relay. They provided this half. You need to provide the connection to the system (ie., the other half).

[Chris Parks]

Use a decent sized cyclone(s), 5hp will do it with at least a 15" impeller and park it outside. The cyclone does the primary separation and then run the exhaust through filters and return the air to the building. The air will suffer a temperature rise but not to ambient. The big issue you might encounter is noise with any dust extractor outside a building, a cyclone if any good is about 90db at the exhaust. By using cyclones you also reduce the need to handle the dusty bags that you would have if not using one. You can dump straight into drums or bigger bags and tie them off after removal instead of having to empty them. Timed bag/drum checking or emptying will overcome the need to know when the drum fills up as a general rule, do it every morning for instance before starting work and design access to make it as easy as possible.

[Kevin Jenness]

For sure, if you exhaust that much air you will have to condition the makeup air to maintain your interior temp/humidity. I don't see how, given that the fire regs are meant to keep a stream of dust-laden air from the interior, you could return the air inside from exterior units without following their requirements for sensors and shutoffs.

[Chris Parks]

The temperature change caused by the air loss depends on how long the extraction is used for. The building mass has a huge effect on the ambient temperature internally and a complete change of air does not affect the internal ambient all that much. I have seen figures on this but it was years ago so I can't quote numbers. If the extractors are working o a continual basis then you have no choice, the air must return to maintain the climate control. 99% of extractors in the US reticulate the air where as in more milder climates the air is just extracted and lost. My gut feeling is the dust levels will not rise doing this and after the change would have a better than even chance of being better if proven cyclones were used along with good filtration. As for the detection system you seek, it does not exist, end of story.

[Phil Thien]

Something doesn't smell right here.

I'm not intimately aware of commercial DC equipment. I've run into a little bit of it when touring smaller commercial shops. But I don't have extensive knowledge of the gear.

BUT, I don't know of any of it that has any sort of lockout if the filter isn't installed. I imagine some units have a micro-switch on a door that will prevent startup if that switch isn't in place (although those units wouldn't likely be found in a wood shop).

But there are new units being sold today with plenums that feed multiple bags and I'm pretty certain there is nothing to prevent an operator from starting one up with one or more bags removed.

The other thing that doesn't make sense is that, most all the fire codes I know of emphasize listing. They (local authority) wouldn't be satisfied with a modified dust collector as it wouldn't meet any sort of UL or other listing.

My two points above lead me to believe you're dealing with a local authority (maybe a fire inspector based out of a local house) that is making up crap as he goes. This has happened to me on a couple of occasions (but not where DC is involved).

You don't want to lock horns with the guys, they can make your life miserable. But to prevent them from coming back repeatedly with new requirements, I'd tell them that you feel you need to read-up on the codes and make sure you're getting it right. So ask them which NFPA standards they're citing, and whether there are any local amendments you need to know about.

I could be completely wrong, there may be something somewhere and I could be clueless.

But I wouldn't be in a hurry to oblige them w/o verifying the facts.

[William Dameron]

Thanks for the info guys.

After talking with the landlord, I think I can narrow down my options to either placing the Laguna units outside, or putting them inside, but modified (unless I can convince the fire inspector that modifying them is stupid). The landlord has a current tenant in another building with an external baghouse, and the residual dust which is escaping is drawing constant complaints from other tenants, making the landlord scared of baghouse collectors. I convinced them that my cyclones would be good enough, but they're still leary, and if I ever accidentally let some dust get out, I'd be in trouble.

Today I'm going to call some manufacturers of differential pressure switches to see what their advice is. Wish me luck...

As for exhausting in or out... I think my building will be somewhat hot in the summer as-is. If I exhaust all my air outside, I'm afraid it might be worse. The one thing about evaporative coolers though, is that air coming in must equal air going out, more or less. So often, in my house for instance, we turn on the evap cooler, and then crack windows in every room we want to be cool. If you leave a window shut in a room, it actually stays hotter, even though the outside temperature can be way hotter than inside. But I don't know if this warehouse will function the same...

Phil - you have hit the nail on the head. On the paperwork which the fire department has, it has a watermark across it which says, "DRAFT". They have pulled this from somewhere, between now, and when I last talked to them several months ago, and it's not even solid law yet. But, like you said, this guy can approve or not approve me on any whim he feels - I really don't want to battle him. Maybe I could eventually win, but right now the name of the game is not to get drawn into a long fight with the fire department, but to get up and running ASAP to draw in some money to help pay the bills. Ugh...

[Jerry Bruette]

William

I help maintain huge dust collectors at my place of employment 100 plus horse power motors and main duct work that's at least three feet in diameter.

Your differential pressure switches won't help detect a broken or missing bag. What we have are called "broken bag detectors". It's an instrument installed in the exhaust side of the baghouse and it detects particulate in the air stream. Our detectors set off an alarm which is checked on. I suppose you could wire it to shut the dust collector off, but then you may have machinery running and creating dust that's not being collected. I think some type of alarm would be needed to alert machine operators that the collector is off.

Our collectors are governed by the Wisconsin Dept. of Natural Resources and the EPA. They set the upper and lower levels for the magnehelic gauge.

These dust collectors also have pulsators for for cleaning the bags. The dust falls to the bottom of a cone and is dumped out using a rotary air lock valve. The valve is needed to maintain the vacuum inside the dust collector.

There are no alarms or switches, etc. to prevent the unit from running if a bag were to have fallen off, or not have been installed. That condition is covered by the broken bag alarm.

[William Dameron]

Jerry - I've been reading about broken bag detectors - I am confused at how they work. Do they monitor the level of dust traveling through the system? And then alarm when a certain dust level is reached? That seems completely backwards - when high levels of dust are encountered is exactly when the collector should be running. Ugh, what a not fun process.

I might be able to convince the inspector to let us use an alarm. Overall this is quite a stupid requirement I feel, because in a relatively small shop like mine, if there's something wrong with the dust collector, you'll know it, because you're right next to it. But, if he sticks to his guns with the auto-shutoff, I think it would shut off all the dust producing machines as well, because they are supposed to be interlocked into the dust collector, so that if the dust collector has no power, neither do the dust producing tools. All this seems like overkill to me, for my relatively small machines, with relatively small amounts of dust, which you're right next to, so you can monitor everything just from being in the same vacinity. For instance, you will know real quick if you're using a tool with the dust collector off, so why have it interlocked? Also, even if you do use a tool with the collector off, you still haven't made conditions right for a dust explosion - I think all of us have used tools without the dust collector attached at some point or another - it takes quite a bit more than using a table saw one time without the collector turned on to create a fireball.

Will

[Jerry Bruette]

The detectors monitor the air leaving the baghouse of the dust collector for any particulates.

If you can picture the explanation I'll try to give you.

The fan pulls the air through the collector. When the air is pulled into the system from the source of the dust it enters the side of the baghouse and goes through the filters (bags or cartridges) and exits the filters through the top(open end of filter) on the clean side of what's called the tube sheet. It then goes through the fan and is blown out to where ever the collector is vented. The detector is usually located between the fan and baghouse or after the fan, depending on the ductwork arrangement.

The filters hang from the tube sheet and below them is the cone shaped hopper with the rotary airlock valve at the bottom. We have compressed air piped into the baghouse above the rows of filters and have solenoid valves controlling the pulsators. The pulsators are controlled by a timer or a photohelic that tells them when and how long to pulsate, this knocks the dust off the filters and into the hopper.

So if you are missing a filter or have one that is leaking it's like a short circuit. The dust isn't captured by the filter and makes it all the way through the system untouched until it hits the "broken bag detector" which alerts the system. You should never have any dust above the tube sheet because it's the clean side of the filters.

I'll try and find some pictures to post and maybe clarify the mud I just posted.

Also I was thinking it might not be a good idea to have a machine shut off in mid operation because your dust collection system has a problem.

[William Dameron]

Ah, I understand now. For something like this to work in my application, I think I would have to build an enclosure around the dust collector, and monitor the exit air. Because it is a cyclone unit, and the last stage of filtration is a large pleated filter, to measure if there is a leak in that filter, the detector would have to be outside of the filter somewhere, yet in a direct stream of air coming out of the collector. I wouldn't mind building some sound enclosures/baffles anyway, so I guess this is an option. But, I believe these things are pretty darn pricey - I just checked on one, which cost $2000. Yikes.

But, the person I talked to from the tech department of the manufacterer of the bag leak detector, said he know of people who have used pressure differential switches, and gave me a manufacter - Dwyer. After speaking with the tech at Dwyer, I think one option would be a pressure differential switch, which would trigger if the filter was removed, which basically reduces back pressure and therefore pressure differential. The pressure switch would then run to an alarm or relay. If the switch ran to a relay, it could be a timed relay, so that the machine would have time to spool up - but if a leak lasted longer than say 10 seconds, or whatever given time, the relay opens, thereby shutting off the machine. All this is too much of a pain. I hope I can find a similar solution or get permission to put these outside.

[Anthony Whitesell]

Ah, I understand now. For something like this to work in my application, I think I would have to build an enclosure around the dust collector, and monitor the exit air. Because it is a cyclone unit, and the last stage of filtration is a large pleated filter, to measure if there is a leak in that filter, the detector would have to be outside of the filter somewhere, yet in a direct stream of air coming out of the collector. I wouldn't mind building some sound enclosures/baffles anyway, so I guess this is an option. But, I believe these things are pretty darn pricey - I just checked on one, which cost $2000. Yikes.

But, the person I talked to from the tech department of the manufacturer of the bag leak detector, said he know of people who have used pressure differential switches, and gave me a manufacturer - Dwyer. After speaking with the tech at Dwyer, I think one option would be a pressure differential switch, which would trigger if the filter was removed, which basically reduces back pressure and therefore pressure differential. The pressure switch would then run to an alarm or relay. If the switch ran to a relay, it could be a timed relay, so that the machine would have time to spool up - but if a leak lasted longer than say 10 seconds, or whatever given time, the relay opens, thereby shutting off the machine. All this is too much of a pain. I hope I can find a similar solution or get permission to put these outside.

The Dwyer rep is headed down the same line as I was. Trying to find the leak in the bag would be impossible. Trying to detect a drop in pressure in the plenum between the filter is really the only way to detect a tear in the bag. There isn't all that much wiring involved in the (simpler) DC starters such that adding the components Dwyer mentioned would not be that difficult. Did Laguna provide schematics of the control box when you purchased the system? Can you get them? Can you post them (or send them)?

[Phil Thien]

Phil - you have hit the nail on the head. On the paperwork which the fire department has, it has a watermark across it which says, "DRAFT". They have pulled this from somewhere, between now, and when I last talked to them several months ago, and it's not even solid law yet. But, like you said, this guy can approve or not approve me on any whim he feels - I really don't want to battle him. Maybe I could eventually win, but right now the name of the game is not to get drawn into a long fight with the fire department, but to get up and running ASAP to draw in some money to help pay the bills. Ugh...

You don't really need to fight them, just ask them to cite any NFPA standards. You don't need to confront them, just say "oh this sounds important, can you please provide me a citation so I can read-up and make sure I get all my ducks in a row?"

They can't make things up as they go. I've had them try, it doesn't fly.