How much sense does this make??? DC question...

[Michael Dunn]

Hey guys!!!

A few weeks ago I bought a new/old Delta 50-850 DC. I plan to pair it with a cyclone from eBay. In reading recent threads here I decided to take a look at my impeller. It appears, to my understanding that there are two 'errors' in this design.

1. I have a 6" inlet, however immediately behind that it is reduced to 4". (See pic...) How much sense does that make?

2. It also appears that the impeller blades are facing the wrong direction. It seems to me, at my current level of understanding, that the blades should be 'scooped' I favor of the direction of rotation in order to more efficiently 'throw' the chips and fines out of the unit and into either a cyclone or a container.

I sure hope this is a design flaw that I can overcome and therefor have even better performance.

It seems that the blades can be removed and flipped 180. Haven't taken a super close look yet though.

So, would I behoove me to make a new true 6" inlet? Would it also be wise to flip the impeller blades?

[Michael Dunn]

Forgot the pics...

[Mark Burnette]

Back-flexed impeller blades aren't uncommon. In fact I think the $200 Harbor Freight DC features them. Not sure how it affects efficiency but I bet they're quieter. You won't be able to simple re-mount the blades since the mmounting holes follow the same curve as the blades.
It's also likely that increasing the intake to 6" will put the incoming stream over part of the blades instead of in the open center where all the suction occurs. Making the inlet 6" does appear to be a little bit of a "cheat" to make you believe this fan is in the 6" class when the impeller size is appropriate for a 4" inlet.

What's the impeller OD & motor HP?

[Michael W. Clark]

That's pretty typical for a backward curve impellor. The other type of wheel you see on material handling fans like this is a radial type. On this one, the blades are straight. They can handle the material a little better, but are less efficient. The backward curve impellor is meant to be a compromise between the straight radial and backward incline wheels used in "clean" airstreams (think downstream of a fabric filter).

There was a thread a while back about some of the HF units having forward curve wheels. They were swapping them out with a BC wheel from Rikon to gain performance. Based on that, I would say your fan is in the correct orientation.

As far as the inlet, I would not do anything permanent to it. I know that portion of the fan is critical to its performance. Larger fans have an inlet cone. The placement and alignment of this cone (+/-1/16") can make a huge difference on performance. You make it better which could overamp your motor, or you may make it a lot worse. I wouldn't do anything that couldn't be undone or fixed.

Mike

[Michael Dunn]

Back-flexed impeller blades aren't uncommon. In fact I think the $200 Harbor Freight DC features them. Not sure how it affects efficiency but I bet they're quieter. You won't be able to simple re-mount the blades since the mmounting holes follow the same curve as the blades.
It's also likely that increasing the intake to 6" will put the incoming stream over part of the blades instead of in the open center where all the suction occurs. Making the inlet 6" does appear to be a little bit of a "cheat" to make you believe this fan is in the 6" class when the impeller size is appropriate for a 4" inlet.

What's the impeller OD & motor HP?

The impeller OD is 12". Motor is 1-1/2HP.

[Jim Neeley]

Michael,

If you increase the entrance from 4" to 6", beyond the start of the blades, you will be giving up performance at higher SPs. You *may* get higher flows at very low SPs; there are too many factors to answer with certainty.

Please understand that it took additional metal (cost more $$$) for Delta to add the reduction, something they'd not do if they didn't think there'd be a gain from it. After all, the extra $$$ comes directly from their profits.

As to whether or not it'd be better in your situation, I've seen people replace the piece you are holding up with plywood and install a 6" inlet. If I had it and wanted to test it, I'd try that before modifying the original.

Just my $0.02.. YMMV.

Jim

[Michael Dunn]

Ok. That makes sense now. It seemed foolish to me at first.


How about this???

I'm running a 6" main duct with 4" drops to each tool. Should I use 6" blast gates and then step down to 4" and then to the tool? Or should I step down to 4" then use a 4" blast gate and then to the tool? Is there a difference?

[Wade Lippman]

I have to think that whoever designed the DC knew more about it than we do.

[John TenEyck]

^ This. If the specs. for the DC meet your needs there's no reason to fool with it. If they don't, you need a different DC.

John

[David Kumm]

Most impellers that sized are mated to a 5" inlet. I would not go from a 4" opening to a 6" main and then 6" drops. You will need smaller diameter verticals with that set up. I would check the amp draw with just the plate on and the 4" opening but no duct or hose and if the motor is running under FLA you could put a bigger opening on it and then use 5 or 6" horizontals. You are taking a machine meant for portable use and trying to turn it into a stationary collector that is usually sized larger to work well so don't expect miracles. Dave

[Michael W. Clark]

I'm running a 6" main duct with 4" drops to each tool. Should I use 6" blast gates and then step down to 4" and then to the tool? Or should I step down to 4" then use a 4" blast gate and then to the tool? Is there a difference?

It doesnt' matter where you put the gate. In your scenario, I would go with 4" gates to save money.

Necking down to 4" is going to cost you on pressure and flow. If you are redoing your duct system, you might consider enlarging the machine ports to accept a 5" or 6" connection. At some point, you may get a larger collector and want the extra CFM that you can get from a larger machine port. The benefit to using metal duct is the availability in the odd sizes. Also, you can use some of the register take-offs for hood connections. You can certainly make your own hoods, but the metal register take-offs cost about $10 each if one will work for you.