# Advice on venting upperbag dust outside the shop



## Falegname (May 7, 2010)

Hello fellow Lumberjocks… I was recently given a dust collector similar to this one

http://www.busybeetools.com/products/dust-collector-1hp-570cfm-1-mic-bag-csa.html

I think it will meet my needs, but I'd like to vent it outside instead of through the upper bag. Has anyone done this successfully? I'm wondering if I will be destroying the dust collector or if it will still function at all without the back pressure from the upper bag. So far the only way I can think of doing this is to remove the upper bag and build some kind of reducer to get it down to a 4" pipe that I plan to put through the wall of my shop.

Any advice is welcome.


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## wapakfred (Jul 29, 2011)

What might happen if that venting will allow the unit to move more air. That may well overload the motor and burn it out. You can test this with an amp meter if you want to stay with that unit. Read the amps and compare the reading the FLA number on the motor plate. In all honesty, I would be surprised if your happy with the performance of that unit. The reducer for the exhaust can be as simple as a piece of plywood cut to fit the DC outlet, then put a 4" (+/-) hole in it to accept a PVC union, secure it with screws and seal it, then pipe your pipe into it.


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## rwe2156 (May 7, 2014)

Fred,

I have vented my blower outside (cyclone) and it works great. I don't understand how reducing the back pressure could overload the motor. I would think it would actually reduce the load. Please educate me! I talked to Jet before doing it and they said there would not be a problem.

Mark,

The only realisitic way I know of is to remove the motor/blower from the bag assembly, turn the unit on its side and add either a cyclone or some other separator. Then just attach a duct through to the outside.

But I totally agree with Fred, on a unit this small I think you're wasting your time.

What are you using it for?

Keep in mind with venting outside you need replacement air which in Montreal is a critical consideration, depending on the size/cost of heating your shop.

My advice is to simply upgrade the filter to a canister, attach a small cyclone and use it as a mobile machine-to-machine collector.


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## TheFridge (May 1, 2014)

I took the collector and put it on a 55 gallon drum. I cut a thein baffle in the drum lid. I melted a Rubbermaid trash can lid to the top with a 4" plumbing 90 in the center, pointed away from the shop. I ran a piece of 5" plumbing pipe outside to the collector/ drum setup with the motor and impeller inside under my table saws extension table. It just spits chips into the yard when i forget to empty it.

Works like a champ.

Edit: lowering back pressure put less stress on the motor.


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## wapakfred (Jul 29, 2011)

Any thing that reduces the resistance to flow in a DC system will increase the amount of air that system can move…..hence reducing the back pressure on the discharge allows more air movement. That (more air), in turn, increases the load on the motor. Like I said, you can test this easily. You will see an increase amperage with an open discharge, it may not be enough to be a problem…but then again it might.


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## TheFridge (May 1, 2014)

Ehhh. Gonna have to disagree there bud. The increase in air flow is just the motor doing more work with less power. Because the airflow increases doesn't mean the amperage does. The induction motor wants to run at or near its rated rpm. Any restrictions or added load will cause it to draw more power to try to keep up. If you ran an induction motor with no load at all it would run just fine.


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## wapakfred (Jul 29, 2011)

You couldn't be more wrong, but I'll leave it at that. You are correct that running it with no load is just fine, now adding air to the impeller adds load, hence more amps as the motor tries to overcome that load (and stay at it's stated RPM). Reducing backpressure at the discharge allows it to add air (and load). But with that, I'm done…..


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## TheFridge (May 1, 2014)

Pretty much an electrician. 15 years. Just sayin.


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## ErnestP (Nov 27, 2015)

One thing to consider, with outside venting…
If your shop is a conditioned environment,
you're pumping all that heat/cool air outside.

As for the rest, you can hook up a cyclone/chip catcher.
Pre-stage it to the blower/impeller.

First, pipe the shop collection to the outside, into a cyclone box. 
Bring the cyclone exhaust back inside, into the blower section's intake.
Let the bags do their job, as a final, fine-dust filter.

I'm assuming, your goal is easier maintenance/emptying.
Noise-reduction, you're best option is an enclosure/closet 
i.e. isolation of the motor/impellor assembly.

Ern


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## clin (Sep 3, 2015)

I think Fred is correct on this one. It's not the motor, it's the blower which is a form of centrifugal pump. Like a squirrel cage fan on your furnace. If you completely plug the supply (or exhaust) of air, the motor will completely unload. It can't do any work if it isn't moving air.

On the other hand, the more freely it can move the air, the more air it will move at a higher speed and therefore do more work loading the motor more. Of course motor characteristic are going to play a role. So it's also not going to be as simple as an unrestricted blower is certain to overload the motor.


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## wormil (Nov 19, 2011)

What I can tell you 100% from experience is that if you allow a fan designed to work with restriction, to pull more air than it should, the motor will overheat. The restriction on a DC should be on the inflow, not the outflow, so venting outdoors shouldn't hurt the motor.

Back on topic, I know 2 guys who vent outdoors. I've been in both their shops during the winter and couldn't feel a temperature change while the DC was running. The reason is that once everything (machines, floors, walls, etc.) in your shop is up to temperature, it will hold temperature even when some air is evacuated. It will be less energy efficient but not as bad as people theorize.


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## rwe2156 (May 7, 2014)

Rick M -

How big were their shops and how much was the DC running?

Depending on the size of the shop, how much the DC is running, and how cold it is outside, and how you heat the shop, it can be a problem.


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## rwe2156 (May 7, 2014)

> You couldn t be more wrong, but I ll leave it at that. You are correct that running it with no load is just fine, now adding air to the impeller adds load, hence more amps as the motor tries to overcome that load (and stay at it s stated RPM). Reducing backpressure at the discharge allows it to add air (and load). But with that, I m done…..
> 
> - Fred Hargis


I believe you but intuitively it doesn't sound right. How can reducing the back pressure allow more air into the system? I would think the only load factor is on the inlet side.

I have no way of comparing filter vs. no filter on my unit, but I am going to put an ammeter on it just for my own info. It's never tripped a breaker but I'm curious now. All I know is by venting outside the performance increaded dramatically.


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## JeffP (Aug 4, 2014)

That's the cool thing about science. No need to "decide who to believe". People have done testing of dust collectors with different amounts of air flow restriction and video taped the results.

YouTube overfloweth with examples of this. Mathaais Wandel of WoodGears has several videos that show current flow readings for same unit with different amounts of air-flow allowed.

Universally, a fan uses more energy when it is moving more air. Agreed, on the surface, it is counter-intuitive that removing an obstacle would increase the power consumption. You could look at it another way…all of physics is beholden to the laws of thermodynamics. One of those laws can be paraphrased as "there is no free lunch". Moving more stuff requires more energy.

Pretty much a degreed Electrical Engineer for 30 years. Just sayin.


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## JeffP (Aug 4, 2014)

Separate answer more specific to the OP question…

Many of us have our DC ported outside rather than filtering the air and sending it back to the shop. It is a very common thing to do. So far (knock on wood) I have never seen a posting here or elsewhere saying "I changed my DC to port outside and it broke right away". Not saying it can't happen or hasn't happened…just saying it is a common thing to do and there is no evidence that it is particularly risky to the health of the DC.

One other point…if you're putting a hole in the shop anyway, consider moving the whole unit outside rather than just porting it outside. Cuts down on the noise considerably.


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## tomsteve (Jan 23, 2015)

something else to consider venting outside is proximity to house. a friend of mine vented his outide. unfortunately he would get a dust coating on his vehicles, deck, and it even got into the house in the summer with all the windows open.
ened up venting into an enclosed trailer.


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## kelvancra (May 4, 2010)

Do some searches and you'll find references to this over and over again. These things are engineered to run with so much restriction. Without it, the motor can run much faster, for example.

That said, there is no reason you couldn't get the same effect by restricting the pipe. Of course, dropping the thing down from, say, a twenty inch output to a six inch or four inch sounds like "no much fun." Then there is the heat or cooling loss, at a rate of, say, five hundred CFM.



> Fred,
> 
> I have vented my blower outside (cyclone) and it works great. I don t understand how reducing the back pressure could overload the motor. I would think it would actually reduce the load. Please educate me! I talked to Jet before doing it and they said there would not be a problem.
> 
> ...


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## kelvancra (May 4, 2010)

Good point (inflow vs outflow). My three horse cyclone talks about not running it without load on the front end, but says nothing about the outfeed. However, could it be it's a calculated balance? After all, restriction, whether at the front or back is going to affect performance.

Of course, switching to finer bags on my three horse, four bagger should be considered an issue to then.



> What I can tell you 100% from experience is that if you allow a fan designed to work with restriction, to pull more air than it should, the motor will overheat. The restriction on a DC should be on the inflow, not the outflow, so venting outdoors shouldn t hurt the motor.
> 
> Back on topic, I know 2 guys who vent outdoors. I ve been in both their shops during the winter and couldn t feel a temperature change while the DC was running. The reason is that once everything (machines, floors, walls, etc.) in your shop is up to temperature, it will hold temperature even when some air is evacuated. It will be less energy efficient but not as bad as people theorize.
> 
> - Rick M.


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## ThomasChippendale (Nov 6, 2015)

Not sure I understand why you would want to vent the upper bag outside, first it is a filter, so if you replace it with a 4 inches pipe, you will be sending the dust outside and keep some dust and heavier particles inside. It will not overload the motor is you put some restriction, 4 inch pipe is a restriction and surely sufficient, those fans can be used simply to circulate air in a 4 or 6 inch duct for air make-up units. Along with the dust, you will be sending a lot of heat also and you will need to make-up for the volume of air lost. If you do not allow air entry, you will starve the dust collector, it cannot pull more than the restriction of air incoming in your room. In Montreal, buildings are well insulated and well sealed and tonight it will be -19C, below zero as we used to say, you would be sending 570 ft3 of warm air each minute and replacing it with 570 ft3 of -19C air, this would work for a freezer but in a workshop, it will get cold and dry.


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## CharlesA (Jun 24, 2013)

I vent my HF DC outside after my Thien baffle-haven't had a problem in about 2 years and I'm very pleased.


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## MadMark (Jun 3, 2014)

Designers always leave a healthy margin in their designs to operate under worst case conditions. The backpressure variation is a 2nd order effect swamped by other factors.

Short version: Don't worry, be happy!

M


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## TheFridge (May 1, 2014)

personally, I wish someone could show me. I've spent 5 fruitless hours looking for answers I already knew. While learning a little bit more about other motors along the way but that has no bearing here.

Split phase motors is what you're gonna look for. Idle or no load conditions. Not universal motors like in a vacuum.


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## REO (Sep 20, 2012)

We run common vacuum cleaners for vacuum panel lifter movers all day long. when a vac is restricted or even plugged it draws less current than when open. More air more current, less air less current. Blowers are designed with applied HP in mind. try it with the wifes vacuum cleaner. turn it on and plug the end. what do you hear? the rpms go up. an indication that the motor is under less load. caution! most of these motors are air over for cooling so do not do this for an extended period of time or the motor will overheat from lack of cooling not increased load. Fridge is right when he says that an unloaded motor will not run at fully synchronous speed because of slip and that it will run without harm all day. He was missing where the LOAD on the motor increases as the volume of air allowed to pass through the Blower increases. Fred missed it with where the restriction has to be. it is total air movement limitation whether it is gaged before or after the fan makes no difference. there are thousands of examples of both dirty side and clean side blowers in the wood working industry out there each has its advantages for the user. Rick pegged the energy loss part of the equation. a bathroom fan averages 100 cfm.


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## TheFridge (May 1, 2014)

You are right.

In the end it depends on the size of the impeller in relation to the size of the motor.


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