Explain Operation If You Can

[HELModels]

http://www.rcgroups.com/forums/attachment.php?attachmentid=719600 There is the link to original thread.

How does it work? Is there enough info in the picture to determine principles of operation?

I am not so sure contact with a switch always means a circuit is on,i.e., a circuit can be normally off or on. The gauge indicates something like negative atmospheric pressure? The location of the tubing, is it important? Is it using a venturi effect? The jar, is it firmly attached or floating? The function of the spring? There is a tight seal in the lid of the jar and spring tension is mildly adjustable, but pipe dope shows it is set. I think it might be helpful to assume there is a vacuum pump on the back side of the vertical board and there is a vacuum bagged wing to the right.

My initial reaction was to agree with another post and that assessment was that the relative vacuum casued the lid to flex and complete/disconnect the switch circuit. My confusion is in whether the lid flexes up under stronger vacuum or sucks down and loses contact. I am also not sure whether the jar is attached or not. Attached would be necessary for the lid flex. Free floating on the spring would indicate some other type of operation.




Here is the picture, since it was uploaded and is now part of the institutional memory, I wont hesitate to attach it.

[Sparky Paul]

If the jar is glued to the base, sucking down inside the jar causes the outside pressure to press the lid into the jar.
I expect the spring is set to maintain a constant negative pressure in the jar and the bag. Suck too much, the pump is turned off, don't suck enough the pump is turned on.

[BMatthews]

The lid of the jar is flexible and will pop in if there is enough vacuum. The spring is a way of setting just when it flexes in enough to trip the micro switch.

I think the confusion is how the motor is switched on. The green rectangle at the left is a microswitch. The thin arm coming off it is only an activating lever and NOT an electrical contact. The switch action and contacts are actually inside the green thing.

In this case the normally open contact of the switch is being used since you want it to switch on the motor when the rising of the lid surface pushes the trip arm upwards towards the body of the microswitch. When that happens the vacuum pump comes on and the evacuation of the air causes a higher vacuum in the jar and the lid gets pulled back in again.

Paul's right about mentioning th jar being glued to the base. It would need to be or else the spring and the vacuum flexing of the lid would easily lift it up.

[HELModels]

Yes, that explains it. Pretty clever device. I wonder if a snapple-type lid would work as well? They pop real nice when the vacuum seal is broken. Would the I.D. of the vacuum line compared to jar volume be critical? I'm guessing it would only matter whether you can practically mate with the jar or not. :eek: Please, I've got no desire to "mate" with a snapple bottle.

[Sparky Paul]

The wider preserve jar top is easier to deflect with small amounts of pressure differential than a Snapple top would be.

[Ricardo RW]

Instead of the jar you can also use those vaccum devices that were installed in old car carburators, they have something to do with the advance... I think.

I bought one to control the pump exactly as the picture posted.

Regards.

[vintage1]

I am sure you are all wrong.

The jar obviously gets lighter as the air is pumped out, rises on tge spring and moves the switch

:D :D

[HELModels]

Screw that, I'll probably go the food saver vacuum route. I have 2hp compressor, but that will require a venturi device and I have no idea how to rig a switch for that type of arrangement.

[space_case]

You will still be tripping the vac switch based on the vac side presseure of the set up. I guess you would need a check valve, also.