Author Topic: Vacuum clamping tubing and fittings.  (Read 1401 times)

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Offline afish

  • Posts: 1326
Vacuum clamping tubing and fittings.
« on: January 14, 2022, 11:15 AM »
Based on another thread I thought I would start a specific vacuum tubing thread.  I am trying to get my system dialed in and the tubing/fittings leaking is my biggest issue.  The clamps still work but the constant pump cycling is annoying me.   

I did some testing this morning and figured I would post some results of the different configurations. Most of my system is comprised of 3/8id reinforced tubing and barb type fitting that terminate to 3/8 ball valves so I can hook different things as needed in different locations such as vacuum bags and clamps.  I know these are leak free since my pump is always on and never cycles. So up to the ball valves its good. However I was having issues with the push to connect fittings which I had on the pods and the pneumatic valve after the ball valve.

I did the tests using the same setup and having 2 connectors one on the output of the ball valve and one on the input of the pneumatic valve. 

6mm test = 6mm fittings with 6mm tubing leaked the worst.  I could audibly hear the leak and it would get worse if I moved the valve or tubing around.  I averaged about a 90 seconds before my pump would cycle.

1/4" tubing/6mm fittings = Since the 1/4" tubing is slightly over 6mm I tried that.  The tubing goes in and is much more snug going in and out but still doable. However long term Im not sure if it will effect the internal o-ring and develop leaks later. This gave me a pump cycle time of 9.5 minutes

barb fittings = I did a control test using the barb fittings too.  I stopped the test/timer at 32 minutes.

4mm = This is where things got a little interesting.  The 4mm tubing with 4mm fittings performed as good as the barb fittings above. I stopped the test/timer at 32 minutes with no pump cycle.  Not sure on longevity yet but I would love if it lasts.  The 4mm tubing is nice its small, flexible and easy to work with and since the vacuum clamps dont need a large volume of air flow it still works well for vacuum clamping.  vacuum bagging not so much.  Im not sure if since the 4mm tubing is smaller more flexible it doesnt put as much strain on the internal o-ring. 

Just figured I would post these results if anyone was thinking of doing their own and I already have a bunch of the tubing and fittings in all different sizes and since the vac sys is going away more may be looking to do their own. 

Oh and the festool quick connects are ruled out on price alone.  They want 60 bucks for just the coupler... I dint even price the other half after seeing that. 
 
« Last Edit: January 14, 2022, 06:29 PM by afish »

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Offline Richard/RMW

  • Posts: 2318
Re: Vacuum clamping tubing and fittings.
« Reply #1 on: January 14, 2022, 12:31 PM »
@afish there are older threads with lots of info on fittings, including alternate suppliers. Basically the quick coupler is the same as a European or high flow pneumatic coupler that is widely available. McMaster has quality fittings around $15 and cheap ones can be found in big box stores.

I'll update with links when I get time.

RMW
As of 10/17 I am out of the Dog business and pursuing other distractions. Thanks for a fun ride!

Offline tsmi243

  • Posts: 275
Re: Vacuum clamping tubing and fittings.
« Reply #2 on: January 14, 2022, 12:35 PM »
Do your push-connectors have a brand name on them?

I've never had leak issues (with water) using the cheap ones, but I can say the John Guest official ones DO feel a little tighter when you put em together.  I wonder if switching brands might be all you need?


Offline afish

  • Posts: 1326
Re: Vacuum clamping tubing and fittings.
« Reply #3 on: January 14, 2022, 06:22 PM »
Not that Im aware of.  I know the majority are Tailonz.  But I have 100's of these things I have collected from various projects.  That crossed my mind too but more than likely the 6mm and 4mm I tested today were the same brand.  I noticed if the tube stays in the fitting for long time it gets slightly deformed on the end.  When I did the test this morning I did make a trim cut on the ends so that wasnt the issue.  I might have just had a bad 6mm fitting not sure. However, I did just eliminate as many as I could, based on past experience these fittings are not 100%

I too have also had good luck with the water variety but I still dont trust them but do have a few on my undersink filter.

I just got done pulling out the majority of the 3/8 soft line even though it wasnt leaking and replaced about 45' of it with 1/2" pvc since I needed a 3rd drop soon anyways.  I still have about 6' of 3/8 tube at each drop location and a ball valve.  So far no leaks and its been on for about an hour. 

Vacuum is harder to get a good seal on from my experience.  Plus there is a much smaller window for the pump to cycle.  Dont quote me but I think the pump comes on at 21hg and shuts off at 25hg.  It doesnt take much vacuum to loose that 4" of vacuum.  So not only is it harder to seal but its much more noticeable on pump cycling. I could probably go hours without kicking on the compressor with a small leak like that.  Unlike compressed air its also harder to hear any vacuum leak unless its real bad like in the 6mm test.  The test that lasted 10min. I could not hear any leak even with no ambient noise and putting them directly up to my ear.

If you are using them in compressed air scenario and have more than a few I would venture to guess at least one has a small leak.  With a vacuum pump that runs continuously you will also probably never notice a small leak but it could effect clamping force of the pod or bag   

Im thinking what Im going to do is mount the toggle switch valve on the bottom right side of my bench and plumb that over to the left side of my bench (since thats the corner where one of the drops is) with some left over 1/2 pvc.  That way when I need the clamp pods I can just take the one drop and plug it into the pvc (this will require one QA coupler) the output of the pneumatic valve will go directly to a 2 port manifold via a short 1/4 nipple and the manifold will have two 1/4 mini ball valves incase I want to use more than one pod at a time.  Or if I want one horizonal and one vertical.  I will try the 4mm push to connect fittings from the mini ball valves to the pod so I will only have two P-2-C fittings per pod.  If im only using one pod I can turn the ball valve off at the manifold.  crossing fingers the 4mm holds up and does as good as they did in the test this morning otherwise I will have to convert that to 1/4" tube and barbs.

Offline Bob D.

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Re: Vacuum clamping tubing and fittings.
« Reply #4 on: January 14, 2022, 10:18 PM »
The short cycling is partly from possible leakage and also because of the small volume in your system. If you added up the total volume it's probably only a few cubic inches, maybe 10 or 15 if you're lucky.

Add a vacuum chamber to your system and it will hold for a long time once you reach max vacuum which will vary with whatever the atmospheric pressure is at the time.

Get a cheap 5 gallon (1155 cubic inches) portable air tank and connect it to your vacuum system. Pipe it up so that you can isolate the tank when you need to relieve vacuum to say reconfigure the clamp pads or change the tubing arrangement.

Now with over 75 times the volume that same slow leak will take much longer to trip the pressure switch on you vacuum
pump.
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Offline afish

  • Posts: 1326
Re: Vacuum clamping tubing and fittings.
« Reply #5 on: January 15, 2022, 08:18 AM »
I have a 4 gallon reserve tank plus whatever is in the lines but yes it is a combination of smaller volume and the narrow range of the pressure switch.  While 4 gallons isnt a lot compared to a 60 gallon compressor. I have noticed vacuum tends to get used up fast.  Even when bagging and I open the valve it only takes a couple seconds before the pump kicks on its almost instantly, and will take a few minutes to fully evacuate a 4x4 bag. Thats with a 4.3 cfm pump and 4 gallon tank. However, I have no desire to add a much bigger tank either, both for space reasons and run time.  While a bigger tank would help reduce cycles it would also just increase run time to refil the larger tank when it does cycle, so its a bit of conundrum. You have to replace every cubic foot of vacuum you use or leak one way or another, either a little at a time or all at once. 

My post was more to let others know to be mindful of leaks and the type and quantity of fittings if putting together their own vacuum clamping set up.  It doesnt take a big leak to make a big difference when working with vacuum even a very small leak makes a big difference and the fittings are the biggest offenders.  The braided line and barb fittings seems to be the bullet proof method which is probably why festool uses it. The smaller pneumatic line with push connect fittings can be hit or miss especially when used in a vacuum situation and extra diligence is needed. 

These small on board systems like the kronos with very small cfm pumps and no reserve would be especially susceptible to fitting leakage issues.  Im not sure of the vacuum pump specs on those small 12v pumps but it cant be much and they have no reserve tank so any leak will result in a pretty big reduction in clamping force. A singular one clamp setup isnt probably an issue but running multiple pods off that tiny pump gives me pause especially when there is push connects involved.  Im also wondering about those small bearing type seals.  When I was looking I couldn't find any that used a O-ring or rubber to make a seal.  They all looked like metal ball on metal seat for a seal.  I 100% would not be trusting that for a good leak free seal in a vacuum set up.  Im interested to know if the ones used in the Kronos system uses some type of rubber inside.  Vacuum and pneumatics is cool and fun addition to woodworking and offers tons of useful possibilities just be mindful before your project ends up falling on the floor or your foot. 

Offline tsmi243

  • Posts: 275
Re: Vacuum clamping tubing and fittings.
« Reply #6 on: January 15, 2022, 12:19 PM »
Do you use any lube at the connections? 

Offline afish

  • Posts: 1326
Re: Vacuum clamping tubing and fittings.
« Reply #7 on: January 15, 2022, 12:45 PM »
No unless you count a little spit  [tongue] the only one that seemed like it would benifit from some lube would probably be the .25" tube in the 6mm fitting

Offline afish

  • Posts: 1326
Re: Vacuum clamping tubing and fittings.
« Reply #8 on: January 21, 2022, 08:17 AM »
So just an update.  I ended up going through and replacing everything up to the last terminal with either 1/2" pvc or 3/8 braided tubing with barbs. The only push connects are on the ball valves you see or the bottom of the pods.  The push connects make it to easy to switch different pods around so I will just live with the minor leakage which wont really be noticed when using the system anyways as there will be pump cycling from the clamping and releasing process anyways.

I put in this vacuum clamping station on one end of my bench (bench is a little rough its been reworked/cut down/changed several times now) its time for a redo but... Either way I installed two valves with total of 4 ports that can be open/closed independently as needed with mini ball valves.  This should cover any combination of clamping or fixturing I need to do.  I have one valve for sucking the part down to the bench and the second valve is for attaching jigs or fixtures to the top of the part if needed independently of the sucking the part down.  I had to add some labels when you are standing close to the bench working you cant see the lever so I was doing some fishing in the beginning, Im sure as I use it more it will become second nature but for now the labels make it easy to know exactly where to reach under and flick the switch.  The open area to the right allows easy fishing of the 4 or 6mm Lines.  The pods I make have some 20mm dowels to locate them in the mft holes.  This works great 95% of the time.  Only time its an issue is if the part is cantilevered alot and you push down it wants to lift the pod out of the mft holes.  I just ordered some TSO power dogs to solve that issue and future pods will have some 20mm holes outside the vacuum area to really secure them down to the top (if needed)