Ducting diameter dilemma

Re: Ducting diameter dilemma

Kent in Emmaus, PA

>Ells,

I used 26 gauge metal ductwork in my shop. Snaplock pipe from hvacommerce.com and fittings from pennstateindustries.com were the best deals I found.

Re: Ducting diameter dilemma

Ells in Boulder

>Thanks, I'll have a look at those sites. I'd expect this to be a growing issues until the manufacturers catch up.

Thanks again.

Ells

Re: Ducting diameter dilemma

Roger Marks

>Hi Ellis, Jan. 2,2007

My solution to this problem ended up

pretty simple. Just ran some 6" duct

on the ceiling where needed and put 4"

drops to each machine. It's been up a

year or so and has worked very well.

Be sure to put a 45 degree angle on

the 4" with a foot or so length connect-

ing to the main duct. This will improve

air flow with less turbulence.

Good luck,

Roger Marks Cedar Rapids, Iowa

Re: Ducting diameter dilemma

Ells in Boulder

>Roger,

Thanks, I appreciate the response. I'd really like to use 5" ports at the machines, any restriction is about the same as having it restricticted all the way back to fan. However, looks like 5" is still rare. I measured 1200+ CFM at the 5" inlet at the collector but barely 550 CFM at the end of a 20ft 4" hose. I suspect it would be about the same at a 4" port at the end of a long 6" hose.

Cheers,

Ells

Re: Ducting diameter dilemma *LINK*

Bob Dodge

>Hi Ellis,

Using the proper size of pipe with your dc, can yield dramatic improvements. 4" pipe is ok with very short "direct" hook-ups, but not good for duct-runs to a stationary small-shop dc. You're limiting yourself to roughly 400 CFM at the hoods of those machines that have a single 4" port. Even using a 6" main won't help get you an efficient set-up. Here's an example.

In June/2000, American Woodworker Magazine, published test-results for a group of dc's. The top-performer in the test was a Jet DC-1200 w/12" impeller, and twin 1 micron filters. That dc managed to pull a "claimed" 1025 CFM through a 10 ft length of 6" pipe. Now, they also tested it "under load", to simulate a small duct-network. Thet used 20 feet of 6" pipe, then reduced to a 6 foot length of 4" flex, and a single 90 degree elbow. Airflow dropped to 555 CFM, and that was probably an optimistic reading at best. This would not provide the required 685 CFM that the 6" pipe needs to produce a waste-suspension velocity of 3500 FPM.

You need an appropriate "balance" between your dc and the machine-hoods, if you're going to optimize your set-up. With most small-shop dc's, 5" pipe is essential. Buying 4" pipe because it's "cheap", or "readily available", is a choice that ends up costing you in performance.

There's really nothing worth saying beyond identifying what your choice is; buy "cheap", or, "do it right". Your Delta 50-760 has plenty of suction to handle even a 6" main to your table-saw with 2-point collection (base, and overarm blade-cover). For all your other machines with single 4" ports, run a 5" pipe directly to those hoods, and you should be a very happy camper. You can reasonably expect a 50% improvement in airflow at those single 4" hoods. Instead of 350-400 CFM, you'll be flowing 550-600 CFM and more (depending on hood type).

Bob


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