Exhausting DC Outside: Is it safe for the motor?

[Scott T Smith]

Here's an experiment for you:
Most shop vacs won't let you completely obstruct the discharge (for this very reason), but if you did, you would notice the motor slowing down. This is because the motor is working harder.

Conversely, we've all heard what it sounds like when you block the inlet--the motor speeds way up. That's because the motor is not working very hard at all.

Rick - that's a great explanation; very intuitive. Thanks.

[Augusto Orosco]

This has become a very instructive discussion. Thanks for all the replies!

I am trying to get the gist of things here. If I understood Rick's statement correctly, the main factors to consider for my question regarding taxing the motor are volume of air to be moved and pressure differential. Everything else being constant, more air to move equals more motor load. Also, the lower the pressure differential, the less we tax the motor.

Now, Tom mentions that "You can [...] increase flow by removing blockage from the inlet (open the blast gates) or outlet (clean or remove the filters)"

That made me think of the following example: Suppose we completely block the outlet: Then we have no air flow, since no air can escape. By opening the outlet even a tiny bit, we would then increase air flow. The more we open the outlet, the more air flow increases, but such an increase could never be greater than what the inlet can allow. In other words, if in our original experiment we had a tiny inlet, the increase in air flow would be small, regardless of how much of the blockage we remove from the outlet.

Would that be a correct statement or am I misunderstanding something?

[Fred Belknap]

I have the 1029Z and I exhaust directly outside through a 5" metal duct. It goes through the collector (minus bags) and the collector is on top of a 55 gal drum. There is 8' pipe going up in the air to dispel fine dust. It is quiet and work great. After running for an hour the motor is just warm to the touch.
Fred

[Keith Outten]

Sixteen years running the same Dust Collector without a bag or filter without any problems. The only thing connected to my DC outlet is a 48" long 4" diameter PVC pipe. This is real world evidence that it works.

Now, the inlet is a different story as Rick explained. You wouldn't want to run your dust collector with nothing connected to the inlet.

[Augusto Orosco]

Sixteen years running the same Dust Collector without a bag or filter without any problems. The only thing connected to my DC outlet is a 48" long 4" diameter PVC pipe. This is real world evidence that it works.

Now, the inlet is a different story as Rick explained. You wouldn't want to run your dust collector with nothing connected to the inlet.

True, Keith. Given your experience and the ones of others who have also posted here, I feel very confident about venting my DC outside!

At this point I am still asking more questions mainly because the explanations posted here are very interesting and are great learning experience for me

[Ed Calkins]

For whatever it is worth (trying to stay out of the "theory debate") my system was designed with Onieda help and parts. My cyclone (V-3000 3 hp) is mounted outside (I wanted the noise and dust outside) and the only thing on the exhaust port is a bird screen I made so the local birds wouldn't try to make a nest in it. According to Onieda this is acceptable and the restrictions on the input are sufficient for proper motor loading and life. Ed

[David Giles]

I like to work my tools so hard that they break. Then I buy a better tool. Alas, even cheap tools are tougher than I am.

If you can break an Oneida dust collector, SMC will add your name to the "tougher than tools" hall of fame. It's a short list.

[paul dyar]

Don is right, the restriction on the suction side will keep it from drawing to many amps.
paul

[Bill Stoffels]

First thanks for this post as it has helped me in my little issue.
I have taped all of the joints and the seams of the duction added 3 6" gates and now have the motor running cooler than ever.
My issue seemed to be that I had too much inlet area open part the seams and part gates leaking badly also I just open 1 machine at a time and its working great.

Thanks to all

[Craig Moulton]

And to get my two cents into the thread, AC induction motors like in our DC's have an upper speed that is limited by their construction (number of electromagnetic poles) and frequency that is powering them. Most that we'll see are either two pole / 3600 rpm, or four pole / 1800 rpm.

+1 for less backpressure = less amperage draw, or power consumed.

Keep in mind that the air flow over the air-cooled motor also cools it. This is different air flow than the DC air flow rate. The overload protection is thermal, so anything that raises motor temp (ambient temperature, reduced air flow, more amps) will bring it closer to tripping on thermal overload.

It doesn't hurt to once a year or so check that the air vents are clean and free of fuzz and dust. A glue brush and vacuum work really well for getting it out.