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Automotive vacuum actuator

Old 06-30-2007, 11:44 AM
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MODEL MFG
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Default Automotive vacuum actuator

Hi There,
I have completed all work except regulator & carrier in my vacuum bagging set up.
Can anyone please tell me how to make automotive vacuum actuator for vaccum pump.
Please give detail photo & list of required items.
I have to made it for 220VAC so please give me suggestions for that also.
Old 07-08-2007, 04:36 PM
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patternwannabee
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Default RE: Automotive vacuum actuator

Hi Manish,

Since no one has yet replied to this thread, I’ll give it a go.

Your best bet is to buy a vacuum switch, but I realize that in some parts of the world, these items may be hard to come by, and shipping can be prohibitive, so if you have to build a vacuum switch, here is one way to do it.

The main component you will need is the vacuum advance. This is an item found on older model cars. You may be able to find one at a junkyard for cheap. You will also need a vacuum gauge and a mechanical switch (more on this later). Additionally, you’ll need some modeling items such as a sleeved pushrod, clevises, wheel collars, wire, etc.

Vacuum Advance:

Not all vacuum advances are the same, but its basic function is to measure and indicate level of vacuum by means of a retracting arm. As you apply more vacuum, the arm retracts farther into the housing.

Mechanical Switch:

I have tried toggle switches, and even a household light switch, but either the force required to move the switch was too much, or the on/off point was inconsistent.

The switch I used (2nd photo, big switch on left) has a long lever. I don’t know what it’s called (it may be a miniswitch). It is rated at 20A @ 250/125 VAC (my vacuum pump is rated at 4.4A, so this was sufficient). The on/off point is pretty consistent, and the lever is weakly spring loaded, so all in all, this was appropriate.

This switch was wired normally closed (push off). Since the vacuum advance arm retracts for increasing vacuum, I had to reverse the direction of the vacuum arm movement. If you find a switch with 3 terminals (other switches pictured), you’ll be able to configure the switch to normally open (push on).

Lever:

The total movement of the retracting arm from min to max vacuum is fairly small, so I magnified it by means of a lever as you can see in the 3rd picture. This also reversed the direction of the movement, so increasing vacuum pushes left and and eventually pushes the switch lever off.

Deadband:

Ideally your vacuum system will be completely airtight, but in reality, you’ll experience leaky bags. If your on and off point are the same, then your switch will cycle often. Sometimes it will be on for less than a second, and repeat only a few moments later. I’ve had leaky bags causing it to cycle every 2 minutes or so. A reservoir is one way to minimize the cycling, but another way is to build deadband in the switch. In other words, you could have the switch deactivate the pump when it reaches 10” hg, but turn on when it gets below 5” hg.

If you look at the 3rd picture, you’ll see the pushrod is connected to the lever with an EZ connector, and on each side is a wheel collar. I crimped the outer pushrod sleeve slightly to add friction. This was necessary to prevent the switch’s spring loaded lever from pushing the pushrod and automatically turning it on. This way, I could set both on and off points for the switch. The setup pictured here turned off at 20” hg and back on at 15” hg.

As for wiring, I’m not an electrician, so I could not tell you how to do it safely, perhaps you should enlist the help of someone more knowledgeable, but it’s just a single line, and it’s either open or closed. I would suggest you wire a household light switch in line with the vacuum switch so you can turn off your system when you’re done.

Notes:

My vacuum advance was intended for higher vacuum ranges . I had to grind off a tab stop to allow the arm more movement, and sense lower vacuum. Even so, the unit doesn’t measure much below 5”hg. For sheeting white EPS Styrofoam wings, you should be in the 5-10” hg range. I suppose I could have taken the housing apart and played with replacing springs, etc, but I went ahead and purchased an adjustable vacuum switch for the 5-10” hg range.

You may have to play with your vacuum advance somewhat to get it to work properly, but if you’re resourceful, I’m you’ll get it to work. After all, it’s not rocket science.
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Old 07-09-2007, 04:09 AM
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Default RE: Automotive vacuum actuator

Hi patternwannabee,

many thanks for your explanation. I was trying to figure out how this system worked.

Your photos brought and old saying to mind and it's "simplify and add more lightness".
If you only have a normally closed micro switch then you just need to flip it through 180 deg. so you use pull instead of push (see drawing). I don't have your experience with this configuration, but I don't see any reason why it shouldn't work.

Regards.

Karl.
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Old 07-09-2007, 11:19 PM
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Default RE: Automotive vacuum actuator

XE521,

Ah yes, had I been completely awake, I, too might have come up with this simple and elegant solution, but as you know how late night projects go..... It's now looking like a Rube Goldberg device.

I did want to magnify the movement (the top connection on the lever is farther away from the bottom connection), so at the time, it seemed like one way to go. Anyway, it does works consistently.

Now for the rest of the story...Even though it was working, the Vacuum advance would just start moving at around 5" hg. I felt uncomfortable about setting the off points so close to the edge of the range, so I bought a vacuum switch which is adjustable up to about 11". This would be good for skinning foam wings. When laminating wood parts, though, I would want more vacuum. So, I installed the purchased vacuum switch in line with the Rube goldberg one with a toggle switch selecting which switch to use. And that way I have two ranges.

I'm a bit embarrassed with the increasing complexity, but it does work, and seems pointless to simplify it now.
Old 07-10-2007, 01:32 AM
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Default RE: Automotive vacuum actuator

Hi patternwannabee,

Rube Goldberg [sm=confused.gif], is he related to Heath Robinson?

Regards.

Karl.
Old 07-11-2007, 12:58 AM
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patternwannabee
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Default RE: Automotive vacuum actuator

Sorry Karl, judging from your writing, I assumed you were an American living overseas. Yes, Rube Goldberg is the American counterpart to Heath Robinson.

Actually, what you brought up got me to question why I built my vacuum switch this way. I actually recall puzzling over this, and there was a reason for it turning out the way it did.

My first version of the vacuum switch looked exactly like your diagram, but instead of the microswitch, I used a household light switch. The hysteresis in the light switch was way too much for the small movement of the vacuum advance arm (if I got it to turn off, it wouldn’t turn back on), so I added a lever to increase the arm travel. Even so, the household switch’s on/off points were not consistent, so I decided to go with the microswitch.

The microswitch arm is spring loaded with no visible means to remove the spring. When the arm is pushed off, once tension is released from the arm, it automatically springs back on. To adjust the on and off points independently, I would have to keep the arm from automatically pushing back, hence the pushrod with the crimped sleeve. The friction prevents the microswitch arm from pushing back, but is easily overcome by the vacuum advance arm.

Since I was already using a lever, I reversed the motion so it would push the microswitch arm off instead of pulling it off. I felt this was a cleaner installation and I wouldn’t have to drill a hole through the microswitch arm.
Old 07-11-2007, 01:59 AM
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Default RE: Automotive vacuum actuator

Hi patternwannabee,

that was only a piece of my twisted humour, hence the smilies.

Once again thanks for the expanation, but I think I'll be taking the adjustable vacuum switch route. Here in Germany a vacuum advance unit will be hard to find and will probably cost me as much as a regular switch. My only problem now is converting the required inches mercury to kiloPascals and finding a suitable switch.

Regards.

Karl.

P.S. I am an expat, but a Brit.

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