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.

[William Dameron]

If it comes to it Phil, I'll try that. But I think that this guy could fail my inspection, citing bugs bunny, if he wanted to. I could try to ask him for details, like you said, and see if it changes his mind at all, but if it doesn't... I could probablly fight it, but the resulting hold-up might really hurt me. For now I'll play along and see what I can achieve to make things go as smoothly as possible, and most importantly as quickly as possible. We'll see...

[Michael W. Clark]

Hi William,
I'm with Phil, Jerry, and the others on the bag/filter switch. We are an OEM of industrial dust collection equipment that includes baghouses and high efficiency cyclones. Personally, I have never heard of the switch your inspector is requiring. The broken bag detectors are very common though and are adjustable to alarm at different dust loadings. This is something you would use on a centralized collector or cyclone and you record events as part of your continuous emission monitoring plan. Its not something you would typically see on an 8,000 CFM system, more like on a 50,000 CFM system or larger.

One thing I would like to ask is in regards to your air flow. If you think you need 8000 CFM, I am 100% certain you will not pull that much flow through cyclones and filters with only 12HP (four of the 3HP units).

If you are in the used market for a central collector, you may find an Aget or Torit system. They do a lot of work in the wood industry on systems this size and may have a system with all the vents configured (I don't work for either, so I'm nuetral there). You will need a backdraft or isolation device as well. If you are returning the air from a central collector, then there are other requirements. People typically do not return air directly from a baghouse, you have additional filtration to polish off any fines and act as a second stage in case you have that bag leak.

If your inspector or landlord is going to be a stickler for NFPA, it will take some time/money to put together a central system that satisfies them. Many shops like yours use multiple single stage bagger units. Get a free login on the NFPA site. You can access NFPA 664 (standard for wood processing facilities) and look through the chapter on collectors.

Mike

[William Dameron]

Awesome, thanks for the info Mike. I'll start looking into the NFPA stuff.

Also, I have always figured that my cyclone units, which are rated according to the manufacturer at 2125 cfm each, on only 3hp each, meaning 8500 cfm between them off of 12 hp, is stretching it. I do think that these 4 units should be sufficient for my machines though, although we'll see. I may eventually incorporate some automatic blast gates to help even more, but we'll see.

Having weighed all my options, I feel like putting the collectors inside is definitely easiest, if I can get around this stupid auto-shut off rule.

If I do locate them outside, I will end up with some duct runs which are pretty long - maybe 50 feet-ish, with a few elbows in there. If that's the case, will I lose too much vacuum?

I definitely want to keep this on the cheap, but effective side, and hopefully not jump into full on NFPA details...

[Michael W. Clark]

I definitely want to keep this on the cheap, but effective side, and hopefully not jump into full on NFPA details...

Take a look at that NFPA reference I mentioned. You want to stay under 5000 CFM/system and go with the open style bagger units. You will get more CFM/HP because you do not have the cyclone loss. If you add 50 feet of duct to those units, you will take a major hit on airflow. Check out industrial auction sites and you may find some of these collectors for low $$, then plan on replacing the filters with good bags, easire to clean.

[David Kumm]

The operating range of a 3 hp 14" impeller cyclone with filters will be in the 700-1000 cfm range. Dave

[William Dameron]

Thanks for the info guys.

I have always guessed that the manufacterers stated CFM's are false, but I hoped they would be higher than 700 to 1000cfm. Oh well, this is what I have for now.

I definitely would like to upgrade at a later date, to an external unit, of sufficient CFMs. But for now, I have already purchased these, and will attempt to make them work, however I can. I believe they will be sufficient. Perhaps if I have many people using the same set of tools on one collector at once, I could run into issues - we'll see. If and when that happens, I'll look into upgrades.

I stayed away from the bag style units, despite the higher CFMs, because of the level of filtration I can get through cyclones. I could be wrong, but my research led me to believe that because the cyclone spins so much material out of the air before it reaches the filter, that the filter could be very fine, without clogging. Since I'm the one who is going to be in this shop more than anyone else, I really want clean air. I'm hoping that these filter the air out well enough that it is healthy for me to be in long term.

Ugh, dust collection is quite a complicated subject, and is expensive. I talked to dust collection engineering firms, and their prices were quite prohibitive. I'm hoping that one way or another I can make this work...

Will

[Michael W. Clark]

Good luck Will and let us know what you find out on the filter switch.

As far as the cyclone goes, it's function in life is to reduce loading on the filter inyour application. This translates to less filter cleaning and less wear and tear on the filter. The dust level in your shop will depend on the filter media efficiency and how well you do at getting the dust at the source. The latterwill depend largely on air flow for agiven hood. You have to keep the filterclean to keep the airflow up.

The commercial woodshops I have been in use bagger units or central systems. Some central systems are cyclones only, some are a cyclone followed by a baghouse. Some baghouses use cartridges, but the dust is on the outside with much more filter area as comparedto the flow. This makes them easier to clean, usually with an automatic system.

I used to work for one of those engineering firms specializing in dust collection. The cost is not related to the flow, so on smaller systems like yours and other commercial shops, the cost can be prohibitive.

[Matt Mattingley]

You might be able to apply over/under amperage shut offs. This would help out with almost everything except for a almost clogged filter that gets a rip in it, and keeps you within the norm high/low amperage . If the filter is removed it would get tripped, if the filter gets to clogged it would get tripped, but a almost clogged, then ripped might keep you in the non-shutdown mode. Maybe a promise for daily inspection and a sign-off sheet would clear this with the fire inspector.

[Steve Rozmiarek]

Is there an allowance for "mobile" units? Put the lagunas on wheels and don't make them a fixture. Might be a whole different regulatory situation that is much more rational.

[William Dameron]

The units are on wheels, but it seems to not matter.

I think I'm going to try to talk my way out of it for now, and if that doesn't work, try to put on a sensor of some sort - most likely a vacuum switch.

But, I have been thinking about using the ivac system, so that appropriate blast gate opens when a tool is turned on, and the dust collector fires up - this also would satisfy the 'interlocked' feature the inspector wants. It will concentrate the suction, which is good, and you can program the run time of the collector if you want, or just turn it on permanently. We'll see, decisions, decisions...

[John Donhowe]

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.... Just a random, late to the party thought: why not drop by the UNLV EE Dept, where you can probably find a bright, eager and hungry student who could easily and economically design and build a circuit to feed the alarm signal to relays which would also shut off power.

[Phil Thien]

Just a random, late to the party thought: why not drop by the UNLV EE Dept, where you can probably find a bright, eager and hungry student who could easily and economically design and build a circuit to feed the alarm signal to relays which would also shut off power.

I'd be careful about implementing any sort of one-off solution that isn't listed with any certifying organization.

Doing so is basically saying you agree a solution is required, but demonstrating that you haven't implemented one known to be effective.

True story: A client was moving into a new office. He had my firm pull new network and phone wiring. I specified plenum-grade insulation on my network cabling because the entire dropped ceiling was being used for return air. The telephone cabling was supplied by the phone guys, it was not plenum grade. My guy pulled it anyhow.

The client hired a security firm to install a system with some bells and whistles. Basically an alarm system with card access and fire detection. Everything to be centrally monitored, of course.

So the day comes for the fire inspection and the inspector goes RIGHT to my cables. Teflon jackets. Then he asks for my plan, and I show him the layout I was given by the architect. I had made some notes with a red marker and we talked and then he stamped my copy of the plans and signed them, and said I was good.

The phone guys lucked out because the inspector figured if the network cabling jackets were plenum rated, the phone cabling would be, too. Nope, just PVC. That got missed. (BTW, the ceiling was FULL of PVC jackets from before these restrictions, so in reality the requirement is kinda pointless in older construction).

He then turns to the security company and says "hey, there are fire detectors." The security guy thought he had scored some points, fire detectors were not required in this case. The inspector wanted to see plans, but there were none, nothing had been submitted ahead of time.

So the inspector said all the fire detectors had to be pulled, and then he'd sign-off. If fire detectors were to be used, a plan would need to be submitted. BTW, in a commercial space, that plan would need sections for testing and periodic replacement of detectors (they become MORE sensitive over the years, eventually leading to false alarming).

So the fire detectors were pulled and left out of the system.

THAT is the kind of mentality with which you're dealing, when dealing with fire inspectors. Just because a plan hadn't been submitted and agreed to, they were now requiring all of the fire detectors be yanked.

My recollection was, the detectors were removed for a time (maybe a month or two) and then quietly reinstalled. I don't believe any subsequent inspections noted them as a problem.

[Anthony Whitesell]

I'd be careful about implementing any sort of one-off solution that isn't listed with any certifying organization.

Doing so is basically saying you agree a solution is required, but demonstrating that you haven't implemented one known to be effective.


I disagree and agree. I agree I would be be careful about implementing a system before you have to. If you install a system based on their word, rather than a cited regulation then you are agreeing to and going to be bound by what they said. I said, they said. On the other hand, depending on the regulation and decision, there may not be a "certifying organization" for this (as yet) unspecified interlock system. A simple "refrigerator" door switch on the filter mounts and a low pressure detector in the outlet plenum does not have much to be "certified".