# Suction Loss at and through Blast Gates?



## Rayne (Mar 9, 2014)

Good Evening LJ's,
I was finalizing my dust collection and noticed one part of my table saw collection to not have as much suction as i thought it should, so I started to check for suction loss and air gaps. I know some (if not all) of the 90 / 45 degree elbows have some loss, so I'll be sealing those up, BUT when I open up my blast gate at the table saw, I felt a lot of air AT the blast gate itself. Is this normal for everyone? And that's not the only problem. For the heck of it, I checked a hose at the longest end of my piping, which was at the jointer / planer and with the Blast Gates CLOSED, I felt minute suction at the tool itself (end of flex hose to the tool). I'm not even sure how that is happening as the gate itself doesn't have holes and should be creating a seal once the DC is on, but somehow the air is going Around the gate? It just boggles my mind how it's creating suction. Can anyone input their thoughts? I'd like to create as air tight system as I can get, even if it means replacing all the blast gates. They are 4" metal gates; no plastic. I'd appreciate the feedback.


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## Kazooman (Jan 20, 2013)

Blast gates leak. I am certain that the leakage varies between manufacturers, but, in my experience, the plastic gates are actually tighter. I consult for a chemistry company and I am a part owner of the building. On average we move about 25,000 CFM of air through the facility. We have several "elephant trunks" that come down to service individual pieces of equipment. That would be the equivalent of a section of hose running to an individual machine. That all have a metal blast gate with a retaining thumb screw to hold it I place. They will all whistle with an air leak until you cut a chunk of cardboard and let the suction hold it in place. Not a faulty design, and not junk components. Just reality. I am certain that there are leakproof blast gates available, but you would not want to pay the price to buy them.

I have plastic blast gates in my central dust collection system, and I am happy with the levels of air flow at each of the stations when the other gates are closed.


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## Rayne (Mar 9, 2014)

Thanks for the confirmation Kazooman. I'll seal up all the 45's and 90's and see what happens then. Worst case scenario is that I buy plastic blast gates and see what happens at each tool when left closed (of course opening one somewhere else to test). I'll respond back after I taped up all the elbows.


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## Kentuk55 (Sep 21, 2010)

I think those metal gates are screwed together. Maybe take them apart and run a thin bead of silicon around the edge creating a gasket, of sorts. Now I might even try that. Good luck. I'll keep watching.


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## mramseyISU (Mar 3, 2014)

The biggest issue I have with blast gates is crap getting in the corners of them not allowing them to shut all the way. I ended up nipping the corners so I could clean them out. I leaks a little but way less than having the gates part way open.


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## WoodNSawdust (Mar 7, 2015)

I found that plastic leaks less than metal gates due to the way the plastic is extruded. I switched to metal to prevent the clogging issue. My metal gates always keep metal in the track so that they never have space for dust to accumulate. Here is a link gate&searchmode=2 to the ones I use.


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## Rayne (Mar 9, 2014)

I just finished sealing up all the 45's and 90's. That really helped the suction at the table saw and am not having any issues so far after a few quick tests. I'll have to test my jointer and planer later to see how much better the suction is at those tools. Looking forward to more project shop time rather than maintenance shop time.


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## Kentuk55 (Sep 21, 2010)

I agree w/u there about shop time is much better than maintenance time. I've had lots of maintenance time here lately it seems, and I'm a bit of a stickler when it comes to "preventative maintenance". Work/Play safe. Keep that dust collector fed.


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## MrRon (Jul 9, 2009)

"Airtight" is not easy to accomplish on a DC system. It may even be impossible to attain. To put the term "airtight" into perspective, I will tell you what is required to attain air-tightness on a ship. There are compartments on board a ship that need to be airtight. To do this, all joints and seams on steel have to be welded 100%; doors have to have rubber gaskets on them and the whole thing is tested using 2psi air pressure to detect for leaks. The manometer has to show zero leakage after 15 minutes. A soap solution is sprayed on seams and door gaskets to check for bubbles which would indicate a leak. If found, it must be made airtight and tested again. A DC system obviously is not going to be put together as stringently as a ship. The best you can do is to tape up all your pipe joints and accept the little leakage you will still have.


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## Rayne (Mar 9, 2014)

Yeah, all the pipes are taped up, which helped increase the performance. I still get leaks at the blast gates, but I may experiment with something that could seal it perfectly without having to modify the gates much. If it works, I'll post it as a new project.


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## Blackie_ (Jul 10, 2011)

When I plumbed my shop with 4" I didn't glue the joints I just pushed them all together and used duct tape to seal the joints around the fittings, just this past week and after my addition onto my shop I had to re plumb for the new addition and repositioning of the equipment, I tore the whole thing down and started over this time going back priming and gluing each joint and I can sure tell the difference, I figure if I add a new machine or make changes I can always cut and resplice using couplings.


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## MrRon (Jul 9, 2009)

> Yeah, all the pipes are taped up, which helped increase the performance. I still get leaks at the blast gates, but I may experiment with something that could seal it perfectly without having to modify the gates much. If it works, I ll post it as a new project.
> 
> - Rayne


If you can take the blast gates apart, you may be able to wrap some thin plastic tape around the edges of the blade. Plastic electrical tape might work; if too thick, you can get a slippery UHMW tape that has a pressure sensitive adhesive on one side . It is only around .005" thick. You can find it at McMaster-Carr under tapes. http://www.mcmaster.com/#76445a722/=xis9gh.


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## Rayne (Mar 9, 2014)

> Yeah, all the pipes are taped up, which helped increase the performance. I still get leaks at the blast gates, but I may experiment with something that could seal it perfectly without having to modify the gates much. If it works, I ll post it as a new project.
> 
> - Rayne
> 
> ...


 Considering I couldn't find much info about blast gate leaks, this is the same idea I came up with, except I didn't think of electrical tape. I was thinking along the lines of hobby craft sticker sheets i could custom cut to create a continuous border around the blast gate blade. That "should" end the issue with all the closed blast gates leaking. The only thing that will leak after that is the opened blast gate, which should be o.k. to deal with. Thanks for the suggestion. I'll use electrical tape first since that is plentiful before I cut up these sheets I just bought.


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## Sweeper (Nov 20, 2017)

For what its worth. I used Taytools self cleaning plastic blast gates. They're inexpensive and do a good job self cleaning. The only leak they have is when the gate is closed. If you hold the gate up to the light you can see an 1/8" x 1" sliver of light coming thru where the self cleaning tongue runs past the gate's frame. To make a seal for that section I close the gate and using a sharpened pencil I mark the curve of the frame on the gate. Then I open the gate and put a bead of liquid rubber along that line. Be careful not to allow the bead to cross the line or it will stop the gate from closing. This will create a seal when the gate is closed.


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## Redoak49 (Dec 15, 2012)

I made my own blast gates and they are tight with very little leakage.


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## Holbs (Nov 4, 2012)

I am with Redoak. I've made plenty of my own 4" and 6" blast gates out of wood, pvc, and hardboard as the gate. No whistling and noticeable leakage. For most of my HVAC duct, I used the grey goop toothpaste stuff to seal the seams everywhere.
In regards to a DIY blast gate, the gate itself has a 0.002-0.004" clearance (I am bad with decimals…but the width of a strip of painters tape or maybe it's width of 2 strips). Unsure what the commercially made metal blast gates tolerances are.


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## John_ (Sep 23, 2013)

Do you have them installed in the right direction?

I have a couple of aluminum blast gates from Woodcraft. The actual sliding part (gate) has a small dimple it in to force the gate so it will seal against the fitting when it is closed. The dimple needs to be facing away from the vacuum side - otherwise, it can leak out the bottom.










Not the best pic - but take a look. Mine have a pretty decent gap in them. The vacuum side is at the top, the tool side is at the bottom and you can see the 'dimple' and the gap where it would leak if you didn't have the blast gate facing the right way. (The dimple and the thumb screw at the other end force the gate to seal)


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## pintodeluxe (Sep 12, 2010)

Metal gates are pretty good in my experience. I agree with John H, they have to be installed the right way. The threaded knob should hold the gate tight to the pipe. Otherwise it will force the gate open as you tighten the thumbscrew.

Ivac and Grngate automatic gates are both fantastic. Those are by far my favorite gates, but I like metal gates too. I'll never go back to plastic gates.


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## Hermit (Oct 9, 2014)

In my opinion, that dimple just acts as a stop to keep you from pulling the gate out to far. The gates come apart and are reversible as explained to me by rockler when i installed mine. Best bet is use both the a/c sealant and foil tape. Especially seal with foil tape directly inside the blast gate where it meets the metal pipe.


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## Rayne (Mar 9, 2014)

I wonder what triggered the revival of my nearly 3 old thread?  I never did seal the blast gates because after taping up all the snaplocks, I have a TON of suction. My jointer and planer throws out the biggest chips and have 0 issues sucking that up from the longest run, so it's running great now. This is good info for others to search for in the future though.

I also use 4" metal blast gates that is spring-loaded with a hook to keep them open, so there is no nub required to keep them open and is also self-cleaning.


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