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| More questions on vacuum http://www.luthiersforum.com/forum/viewtopic.php?f=10101&t=21690 |
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| Author: | BobK [ Sat Mar 28, 2009 10:24 pm ] |
| Post subject: | Re: More questions on vacuum |
Would it be feasible to detach the pump, fill the reservoir with compressed air, submerge it in water and look for bubbles? Or maybe run a bead of silicone over the joints let cure and run the test again. I coat all my wood or mdf jigs with silicone and I'm able to pull mid 20's (according to my gauge anyway). If you have one suspect joint you could try wrapping it in modeling clay (or moretite rope caulk - borg weatherstripping aisle - this also works well when attaching fittings to wooden fixtures). That might help you pinpoint the problem. One last thought, maybe run the pump directly to a jig and see how long it hold a vacuum after being turned off, the leak could be at the pump. I'm planning on making a reservoir for my pump as well so I'd be interested in any other suggestions, results or construction tips. BTW, nice looking set-up. Should be great once the problems are ironed out. Bob |
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| Author: | Jim Watts [ Sun Mar 29, 2009 12:05 am ] |
| Post subject: | Re: More questions on vacuum |
Filippo, You really don't need the reservoir. That should be a continuous duty pump, and it's going to be running almost all of the time anyway is my guess. Vacuum pumps don't mind running unless they're sucking a lot of air. It's probably harder on the pump to stop and start all the time vs just staying on. 20 inches is fine BTW. |
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| Author: | John How [ Sun Mar 29, 2009 2:18 am ] |
| Post subject: | Re: More questions on vacuum |
He's got a mac valve on there that stops and starts the pump as the vacuum drops by about 3 or so hg, so once the leaks are plugged it should only turn on about once every 5 minutes or so when in actual use with a vacuum clamp. |
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| Author: | woody b [ Sun Mar 29, 2009 1:47 pm ] |
| Post subject: | Re: More questions on vacuum |
I don't have any expierence with vacuum clamping but I've got alot of vacuum experience. I've done (and still do) alot of automotive HVAC work. Your vacuum drop does indicate you've got a leak, however barometric pressure(and allitude) has a big effect on the total amout of vacuum you can achieve. Don't be surprised if you never get to 24"hg even with all your leaks fixed. The evacuation system I use on HVAC systems is rated at 30" but that's at sea level. I rarely see anymore than 27"hg. You might find your leak by pressurizing the system and spraying soapy water on all the joints. |
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| Author: | Brock Poling [ Sun Mar 29, 2009 9:26 pm ] |
| Post subject: | Re: More questions on vacuum |
You flowed medium CA into all the PVC joints? What about the plumbing connections? |
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| Author: | npalen [ Mon Mar 30, 2009 1:23 pm ] |
| Post subject: | Re: More questions on vacuum |
An advantage of a reservoir is when you're clamping a part that doesn't make a perfect seal with the fixture. The inrush of air supplied by a reservoir may let the part go ahead and "grab" to let the gasketing do it's thing. The gasketing would normally let the part grab without a reservoir but on large parts this doesn't always happen. Nelson Palen Edit: probably should say "outrush of air". I forget to think of vacuum as "reverse pressure". |
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| Author: | Bill Greene [ Mon Mar 30, 2009 2:53 pm ] |
| Post subject: | Re: More questions on vacuum |
I had the same issue with mine for a little while... and I ended up having to significantly tighten the fittings more than what I had done initially. Those things need to be very tight, and make sure to use teflon tape. As for the reservoirs, I leaked warmed (thinned) epoxy into those joints and it sealed right up. Now my reservoirs "appear" to hold almost indefinitely. Now getting my vac press to stop leaking is another story entirely. Grrrr.... |
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| Author: | Marc [ Mon Mar 30, 2009 3:24 pm ] |
| Post subject: | Re: More questions on vacuum |
Filippo, I made one of those a couple of years back, stick with it you'll find the problem, the reservoir system is really worth it. Might cap off the fittings from the tanks and isolate the problem. If it were me, and I was certain it was the tanks, I would probably just make another set of tanks. |
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