A few years ago I purchased components for a vacuum veneering system – pump, fittings, filter, … Spent $400 for a 5cfm system, which saved only $300 over a Vacu-Press system and has never worked as well as hoped. Drawback is the vacuum switch. I’m using the same brand I see listed on www.joewoodworker.com site and it sometimes shuts off at several inches of vacuum less than the set point, sometimes never shuts off. It’s a simple mechanical switch based on a Honeywell diaphragm switch, and all they make.
I’ve searched other manufacturers of vacuum switches on the Internet and found “mechanical”, “electrical-mechanical”, “electronic”, “solid state” with no clear presentation of the differences. Prices seem to range from $15 for the one I have to $300+.
A neighbor suggested the switch I have has an internal spring to snap open and closed contacts rated for 5 amps without arcing, and that it may have too much inertia for the use. Even with inertia, seems like the switch should open within an inch of the set point.
Attached is a picture of the vacuum hardware I have. 3/8″ hose connects the rotary vane pump, one way valve, gauge, filter, switch, and vacuum reservoir.
Technical support has not been helpful the manufacturer’s sites I’ve tried, and locally there don’t seem to be anyone knowledgeable on the subject. Does anyone have a technical background or product knowledge that can help?
Thanks.
Replies
I found an old medical vacuum pump a few years back and made a vacuum veneer setup using using 10 mil vinyl material, I did have a vacuum gauge, but not a vacuum switch. What I did was purchase a programable timer switch, the kind you would use to turn lights on and off, etc. This particular switch could be programed for an infinite number ( I think ), on - off cycles. Anyway, after some trial and error was able to program the switch to maintain not less than 20 hg. Typically would run for 1 - 2 minutes and off 6 - 7 minutes. This set up has worked fine for me, for occasional use.
Robert
Have you tried replacing the switch? They are not very expensive. If you are concerned about the amps of the pump maxing out the switch, you could use a control circuit and a relay, and draw next to no amps. You could even switch to a DC control circuit. I have the same switch on my system, and it works fine. My pump probably draws less amps then yours though. Moving parts will wear out, I'd try replacing it first, but if you're drawing over the rating on the switch you going to have problems unless you go to the relay.
My pump is rated at 4.2 amps at 120V so I'm not worried about that. I would definitely like to replace the switch, and am willing to add transformer and/or relay, but need help specifying among electrical, mechanical, electrical-mechanical, solid state, ... and deciding what price point is the minimum for good results.
I think I'd just buy the switch from Joewoodworker and try it. Could easily be a faulty switch right out of the box, sure wouldn't be the first time.
Don I should have asked, how inacurate is it? You can expect any switch to have a deadband, and the Honeywell's is something like +- 4% at 21 Hg. I'm sure the more expensive the switch, the more you can expect out of it. My switch, which I bought from Joe, is set to run to 21 Hg. It then restarts at 18 Hg. It seems that it would be easy for something to get into the switch and goof it up, although I see you have a filter ( I think) so you are probably protected.
Steve
Edit to add, If you don't have a vacuum damper installed, they can make a rotary vane system work better, according to Joe. Might be a reason for inconsistancy.
Edited 10/4/2005 8:54 pm ET by dirtstirrer
This is the 3rd Air Logic switch, and it's the worst of all. Hence my interest in another brand and/or type of switch. Thanks.
I just did a google, and Honeywell makes a couple different models. One of them has gold contacts, and is more sensitive. Unfortunetly, I clicked away before I could copy the URL, duh. You should be able to find it easily.
I think the damper I mentioned before might help, if your symptoms are on/off/on/off cycling near the dialed in Hg, or if you are getting no consistancy. Joe carries them for not much $. Cheaper then a new switch. Rotary vane pumps are supposed to be more quirky for some reason, and that damper is said to really help.
Steve
Check with Whitman Controls of Bristol CT. (860) 583-5293 Several years back I was looking for a vac switch and stumbled upon them. Their local service rep will help you select a switch that fits your needs. I found their tech service to be second to none. Best of luck. Also has anyone tried the new Glad storage bags for a vac. bag? I talking about the ones for storing blankets and other bulky items, not the freezer bags.
How is it wired? Is it wired for normally open or normally closed? I had the same trouble with my set up for the longest time. I must have tried 3 switches. I can't remember which side of the switch the pump needs to be wired into but "my logic" says that the switch needs to be wired to the normally closed side. Based on the fact that I think it should be one way try it the opposite way and I bet that it will work.
Good Luck,
Tom
If I am seeing the set up correctly there are a couple of things to consider.
1. Any vibration in the vacuum line can cause the switch to open prematurely.
2. It appears your filter is located on the pump side of the switch, exposing the switch to unfiltered air.
Been out of the instrumentation business for a few years and don't have any recommendations as to brand, but switches such as these (very low pressure) are notoriously inaccurate. If not too expensive I would recommend the solid state/electronic switches. They tend to be much more stable, less vulnerable to vibration, etc. HTH
Chuck
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