Thread: Cyclone options

A good old cast iron unit, there would be some noise damping from the housing when compared with a thin sheet housing.

The table shows that the blower should be able to deliver some good air flow, it just depends on what the final pressure loss is for your system, if you can keep your pipe sizes large 6" (or larger) bends long radius, flex hose short, minimum fittings, machine cabinet/hood entry points well designed with bell mouth or long tapers you might be able be able to run the blower at around 2500rpm with input of 1.07kw and less noise as a result, if you have a greater pressure loss, (which is more likely than 2") say 8" then you will need to run the blower at around 3500rpm and input 3kw and a lot more noise, and to make things more interesting the more complicated the ducting becomes, (blast gates/duct/ machine hood/hose) to each machine you end up with a whole bunch of system losses so what is ideal for one machine is not for another, (good flow for one machine ,not enough for another) this is where a VSD is good value so you can set the speed to suit a given application, but that means testing to see what you have in terms of flow for each machine.

The blower does look like it could be mounted on top of the cyclone, because of the belt drive your total hieght looks like it might be less than if you were to mount the fan direct onto the motor output shaft like I have done, you would have to pick up the feet mounting with suitable brackets or alternatively maybe use some of the front housing bolt holes. I can't see if the motor has a foot mounting, if it's flange mount only that means mounting via the flange and a different bracket system.

Another alternative is mount blower and motor on the ground and run duct up to the top of the cyclone, doable but more ducting bends etc etc, I would give this some serious thought tho especially if you have the height above the cyclone, if you use a bend radius of 1.5d with 150 pipe you need about 230mm, (not including any installation height) 230 would certainly be less than a fan/motor assembly and maybe less than your blower with the belt drive.

Pete

Bob - thanks for the reminder on noise for straight bladed impellers. I've dug up some fan curves for the blower, which has some noise specifications as well. I thought I'd posted this in my first post as a pdf but had not done so. Apologies.

B series fan curves.jpg

Pete - you raise an interesting prospect in mounting the cast iron blower atop the cyclone. I could remove the inlet side plate from the blower and direct mount to the cyclone. Complications would be establishing the belt drive and tension arrangement, slightly higher profile (vs flange mount motor on fabricated volute) and total supported weight. Advantage would be variable speed via pulley ratio, and reduction in cyclone fabrication time.

Appreciate all of your feedback and suggestions.

Thanks and regards
John

I looked at you impeller fan curve and then re-read your first post and just realised this

Originally Posted by jcge

I'll need 18m of ducting from most distant machine (36" bandsaw) to external exhaust point.

A BP style cyclone is going to require 2.25" WC pressure.
According to BPs Static Calc program to move a nominal 800cfm , 18m of 6" ducting is going to need 2.57" WC pressure.
This means you will need 4.82" to overcome these two basic needs.

AT 800 CFM the fan generates only 6" WC meaning you only have about 1"WC left to overcome port and junction resistance.
This will probably not be sufficient to over come these resistance so the actual flow in that long duct will be more like 600 CFM, and it might also mean that the cyclone separation won't be as efficient.

In a 6" pipe, a 600 cfm has a linear air speed of ~3000 FPM which is below the nominal 4000 FPM needed to maintain sawdust chips in suspension.
I have successfully run around 500cfm through a 6" pipe up to about 6m with a 2HP DC, its fine while its running but if the air flow stalls when the duct is carrying a load (i.e. a power failure) that sawdust will fall to the bottom of the duct and 3000 FPM will not pick it up again.

Your impeller and motor appear similar to those of most 2HP DCs and these are not really recommended for ducting runs of more than a few meters.

If you decide to proceed then it might be useful to build in a couple of inspection ports along the ducting where a compressed air line can be inserted to fluff the sawdust up so the air stream can pick it up.

The fan curve for the B60 looks to indicate that that size fan run as a direct coupled unit (2850rpm) is borderline for the recommended flow, the chart in the first post shows that there is flow available at a high enough pressure to overcome the losses that Bob points out, the difference as far as I can see is the the need for higher speed and power requirement for the direct drive arrangement to achieve the flow. Not too mention the noise!

Which way to go? The motor you have is adequate size (3kw) and flange mount is good if you decide to go with making your own fan and volute/housing which you can mount it direct onto the flange, I would suggest making a shrouded fan with backward curved blades and at least 15" dia. or larger, increasing the diameter will deliver higher pressure, so will higher speed via a (VSD) if direct coupled. Mounting at floor level is still an option if the height is an issue.


Pete

Bob - thanks for clarifying the likely pressure losses and flow limitations, and likely deficiency of the cast iron blower in that regard at the published speed.

Pete - agree that upping the speed of the cast iron blower is an option, and I have a larger spare 3kw motor that I could achieve that with, albeit with an increased amount of noise.

I'm leaning towards making a 15" impellor, and using the flange mounted dual speed motor atop a cyclone. I'll do some reading on the relative efficiency and noise emissions of straight vs backward curved vanes. Presumably the noise levels are primarily a function of tip velocity, volute tongue clearance, and angle of vane inclination.

I really do appreciate the feedback you guys have given.

Regards
John

Regards
John

If you are looking at fan blade design the best shape for a blade is the same as an airplane wing which gives the best performance but the most complicated to make, the next best is the curved blade and the most practical of the curved shape to make, I machined some steel pipe from which I cut sections out of to form the blade, some rolled flat sheet would be equally good, the flat blade variations are generally down the low end in terms of eff.

If you want to make an air-raid siren have the blade real close to the gore point (the closest part of the volute to the blade) too far away tho and there is a tendency for air to go around the volute more than just once, things to consider in relation to noise reduction is having the gore point either at an angle or with a central vee or with fingers, basically some means of breaking up the pulse of air that impacts the gore point produced by the blade.

In respect to the power input v flow power is cubed, so to get more flow from a given fan it can be sped up but there is a requirement for a lot more power, this where your cast blower unit isn't quite up to the mark, so if you can run a bigger fan a little bit slower you'll get the flow you want without wasting power, ideally you want a fan to be operated right at the max eff. but in reality .......



Pete

Thanks for the follow up Pete...I'm definitely not looking to build an air raid siren...my strait blade jointer and thicknesser are close enough to that already.

Regards
John