Cyclone dust collector blower position

[Michael W. Clark]

Thanks for all the ideas (simple home made manometer is more my speed(budget))

Carl, you can definitely build the manometer, but not sure how you intend to measure flow with it? You could measure SP and know that if you increase your fan flow, and the system does not change, you will see a higher SP at the fan inlet. I may be mistaken, and it won't be the first or last time, but my experience is that manometers only measure differential pressure, they do not measure flow or velocity directly. You will need a pitot tube, orifice, or some device that creates a certain DP that corresponds to a CFM.

It sounds like you may have an undersized fan. Low flow through the cyclone has a dramatic effect on efficiency. This is where it would be nice if manufacturer's would at least give you a cyclone DP at a given CFM. If you had this information in your case, then the water manometer could be used to measure DP across the cyclone then calculate the resulting CFM. Maybe Clearvue would give you this? The other thing you can do is measure your fan motor amps. If they are pretty much maxed out (approximately equal to FLA on the fan motor nameplate), then you probably have too small of a fan. If the fan amps are low, then either the motor is oversized or you have a flow problem caused by your system.

Its tricky to trouble shoot a system when manufacturer's don't provide any performance data. How do you know when it is working like it should? I would start with checking the fan amps if you have an amp meter.

You probably don't need to build the manometer for 96" of DP. My guess is that you would have a max of 10-12" at the cyclone inlet. If you build it for 24", that should be plenty.

[Carl Beckett]

Carl, you can definitely build the manometer, but not sure how you intend to measure flow with it? You could measure SP and know that if you increase your fan flow, and the system does not change, you will see a higher SP at the fan inlet. I may be mistaken, and it won't be the first or last time, but my experience is that manometers only measure differential pressure, they do not measure flow or velocity directly. You will need a pitot tube, orifice, or some device that creates a certain DP that corresponds to a CFM.

It sounds like you may have an undersized fan. Low flow through the cyclone has a dramatic effect on efficiency. This is where it would be nice if manufacturer's would at least give you a cyclone DP at a given CFM. If you had this information in your case, then the water manometer could be used to measure DP across the cyclone then calculate the resulting CFM. Maybe Clearvue would give you this? The other thing you can do is measure your fan motor amps. If they are pretty much maxed out (approximately equal to FLA on the fan motor nameplate), then you probably have too small of a fan. If the fan amps are low, then either the motor is oversized or you have a flow problem caused by your system.

Its tricky to trouble shoot a system when manufacturer's don't provide any performance data. How do you know when it is working like it should? I would start with checking the fan amps if you have an amp meter.

You probably don't need to build the manometer for 96" of DP. My guess is that you would have a max of 10-12" at the cyclone inlet. If you build it for 24", that should be plenty.

Thanks Michael,

I was simply going to chase around the piping with the manometer, to get an understanding of the relative restrictions. If there was a particular segment that was creating a high pressure drop, I would first focus on that.

I dont have a good amp meter for those currents.

Kinda shaking my head about all this (and will admit up front that I want to cheap it). But by the time I buy an amp meter, a anemometer, and a dust particle counter - all for the purpose of analyzing/designing the system - there is no $$ left to purchase the actual equipment.

Im understanding more why some choose to just get a really big blower, attach really large dia ductwork, and be done.

[Michael W. Clark]

Yes, take a SP at multiple places and look for anything abnormal. This is what we would do when trying isolate a section of duct that may be plugged. You can drill small holes in the duct and cover it with tape.

[ian maybury]

There's a mountain of truth in what you said Carl: 'Im understanding more why some choose to just get a really big blower, attach really large dia ductwork, and be done.'

Not only does marginal CFM leave you struggling to get even decent chip collection, it also means that (if you do manage to find the sweet spot where it will work) that quite small changes in resistance caused by filter blinding and that sort of thing have a disproportionately larger effect than is the case with a larger diameter impeller which gives not only higher CFM but also has a lot more pressure capability....

It's possible too to build a system using larger capacity stuff for not a lot more money if you put the time into digging up used or discounted stuff too.

I don't mean to brag - but honestly: moving from a 1kW mobile bag filter to a Pentz style 160mm ducted/16 in impeller has been such a breath of fresh air. All of the fuss, bother and pernickedtiness just falls away. It works so much better even on stuff like a router table that doesn't seem to need so much airflow. The Incra port is only 2 1/2 in, and airflow through the fence is fairly restricted - as is often the gap down through the router plate around a cutter.

It doesn't really matter though, because the extra pressure/suction the big impeller delivers means it's pulling a lot more CFM than it would on more typical systems - and even at that there's more than enough spare puff to run a supplementary 4in flexible with an intake hood that can be placed where needed...

ian

[Michael W. Clark]

I definitely agree with Ian. There are not many situations in woodworking dust collection systems where more CFM hurts. DC is getting to be more like other tool purchases (if not already) where you may try to buy the best you can afford at the time. The newest may not always be the best. If you come across a good buy on a used cyclone and fan, then add a good after filter, you would likely be better off than buying a new single stage system. Sure, you will have some time configuring the used equipment like you want, customizing the setup to get the dust drum out, etc. However, you will have less time invested trying to squeeze every CFM you can out of an undersized fan or system.

But homeowners are not alone in this, many industrials try not to spend money on dust collection. I worked the past few years for a company where we mostly tried to improve DC systems that were undersized to start with. Sometimes the owners were willing to invest in major modifications, but most of the time, they wanted to optimize their existing system and make comprimises.

[Eric Tyira]

I'll add that the air going into the blower is at standard conditions (normal temps, sea levels, etc.) while the air coming out is compressed. That's why the "push" from the blower feels like more air than the intake. It's the same amount of air molecules being moved, just more compacted on the outlet side.

[Michael W. Clark]

Yes there is a slight density difference on the inlet and outlet due to the difference in SP. However, the "push" you are feeling is a pressure known as velocity pressure. Velocity pressure can be equated to duct velocity, this is how a pitot tube is used to get duct velocity and then CFM (knowing the duct area). Its the same force you feel when you stick your hand out the open window of a moving car. If your air velocity is 4000 FPM on the inlet and outlet, you will feel basically the same "push" in both ducts.

On the inlet of an open duct, velocity goes down drastically as you move your hand away from the duct. This is mostly due to the fact that the open duct is drawing air from all directions, i.e. front, back, side, behind it if possible. On the outlet, all the air is basically moving in the same direction, out. This is the premise for the "straw example" to illustrate how close your hood needs to be to the source to capture the dust. The better your hood design, the less wasted air being pulled from around the hood, and the more air being pulled from the dust source.


Mike