Hose Clamps and PVC

[Dave in MArkham]

I am having a silly and annoying problem. I am in the final stages of hooking up my new cyclone DC system, and I need to connect 4" grey PVC flex hose to 4" aluminum blast gates. Using normal stainless steel clamps, it it hard to get the PVC to grip tightly onto the lip of the blast gate. I considered trying those double wire clamps (BB sells them), but I have been told they are cheap, and the tightening screw strips its threads easily. What about drilling a hole in the blast gate lip, putting in a small metal screw, then threading on the PVC, followed by the clamp?

Any suggestions would be appreciated - there must be a solution to this that will hold securely. Thanks.

[Allan Johanson - South Su]

You aren't choking down a nice cyclone with 4" ducting, are you? The poor thing, being forced to run a marathon while breathing through a tiny straw.... http://www.canadianwoodworking.com/forum/images/smilies/wink.gif

I use those crappy wire clamps, and only maybe 1/4 of them have broken the crummy bolt when tightening. So if you try them, buy some spares. http://www.canadianwoodworking.com/forum/images/smilies/smile.gif But they do seem to hold quite well most of the time. I think it's because they can apply pressure BETWEEN the ribs of the ducting, and a band-type clamp may not fit between the ribs.

The only problem I can see with the screw idea is that you might contribute to clogging the lines with a screw protruding on the inside of the ductwork. Some shavings might get caught on it if this duct run goes to a jointer or planer. Regular small sawdust particles shouldn't pose a problem.

Some aluminum blast gates have been known to leak like crazy. If you suspect this down the road and want better ones, consider making your own. This can provide three benefits I can think of right now:

1) You can make them so they don't leak
2) They can have longer flanges to ensure a more secure fitting
3) You can make them to have as wide an ID as possible so they don't contribute to restricting the lines like store bought blast gates. For instance, if you are using solid pipe for part of your duct run, you can make the ID of the blast gate be the same as the pipe connecting it by making the blast gate go on the outside of the pipe, not the inside like you are doing now.

Good luck!

Allan

[Dave in MArkham]

Hi Allan,

Thanks for the comments. I guess I'll try the double wire clamp thingies, and buy extra as you suggest.

My system is 6" 26 ga. metal duct all the way from the cyclone to each drop. At each drop, I neck down to 4" and install a blast gate. Then there is just a foot or two of PVC to the machines. I know bigger inlets are better, but all my machines have 4" dust ports (or 2.5"), and I don't feel like retrofitting them with bigger ports. At least not yet - I want to see how this works out first. The 6" ducting does not make long runs, and there are few 45 deg. turns, so I should be OK - we'll see. I should have the 220 v. hooked up sometime this week, then I'll know. Cheers.

[George]

If I understand your problem properly, there is a tendency for the PVC hose to slip off the flange of the gate, due to inadequate clamping force. In my shop I use rosin all the time as a high friction intermediate for connecting things that need some extra tack. I use a lump of cheap violin bow rosin (obtainable at any music store that sells violins for about $4.00). It comes as a solid lump so just powder some by scraping with a sharp edge and spread the powder on surfaces to be joined. You will get a remarkable amount of extra tack. It is not sticky so to speak, and is easily removed with alcohol. The powdered rosin used in sports might be similar but I have never tried it.

By using rosin you should be able to use less clamping force (thus saving clamp damage) while eliminating the tendency for the hose to slip off.

[Bob, in Lachute, Qc.]

Hi Dave, Good luck with the hose clamps.

Just wanted to say that the 4" hook-ups, maybe are convenient for you at the moment, but that's definitely a no-no , performance-wise. It really has nothing to do with how short that length of 4" flex is. It's strictly the over-all area of the opening area of the duct.

When you reduce from 6"-4", you are reducing the total area by 55%. That also goes for your airflow. Suction may appear strong at the inlet of that 4", but once the air hits the 6" portion of ducting, speed will be reduced to the point of clogging. If your system pulls 400 cfm through 4" pipe, velocity through the 6" main, will be about 2040 fpm. Recommended minimum for a horizontal 6" pipe is 3500 fpm, and 4000 fpm thrugh a 6" riser.

If you have to stick to that 4" hookup at the machine, just buy an inexpensive HVAC wye(6"x4"x4"). Run one 4" to your machine, and the second 4" to another machine, or simply leave that second 4" open. The combined two 4" pipes, will flow the proper amount of air to the 6", to make it work at the correct velocity.

I have no idea what dc you have. If you referred to the Pentz cyclone, your numbers would be different, but proportionally the same, percentage-wise. You'd have to pull 800 cfm through that 4" flex, to make the 6" main work properly. That would mean close to 9,200 fpm, through the 4" pipe.

In order for it to work, the dc would have to be able to pull the same as it would, using 6" pipe, multiplied by 4.84 times the resistance. It's a squared relationship. (2.2 x 2.2 = 4.84) times the original SP.

If you're pulling 1100 cfm through that 6" pipe, then the velocity through the 4" portion, would have to be a whopping 12,601 fpm. I'd guess that would be roughly 22"to 23" SP. Noooo wayyy, Joseeeee.

All the best, Bob

[Garrett in Victoria]

[Dave in MArkham]

Hi Bob,

Good to hear from you again. I am the guy that got the 2 hp cyclone on sale at Busy Bee for $599 - remember? I have not forgotten your earlier advice to me on the whole matter of airflow. So what I did was run 6" vertical drops down from the 6" main duct to 6-4-4 Y connectors. Then I put a blast gate on each of the 4" branchs. So as to not starve the system of airflow, I plan to open both gates on the Y, one for the machine in use, and its neighbour for more airflow. That should get about 800 cfm moving through the main duct, which is what I think I need. When I get the whole thing up and running, I'll try and post some pics, and let you know how it appears to be working. Thanks again for the words of wisdom. Cheers.

[Bob, in Lachute, Qc.]

Hiya Dave, I'm gittin' ta be an "old fart" now, got a memory like a seive.;-))

How's that dc workin' out??? Are you happy with the flow????

That 6x4x4 should work out great, as long as your run is not too restrictive. Did you put some 6" blast gates on the drops, too???

Even if you close both 4"'s on one drop, it would be the same.

Hope that dc's workin out well for you.

All the best, Bob