"Pounds on Wood" wrote...
Cupla things Joe. First is that you need a switch with a greater ON-OFF
differential.

Right. The term I was going to use was "hysterisis", but I figured
that would make most readers' eyes glaze over.

That can be done with two switches,

Upon reading the specs for the switch I got, the company makes one
with two switches in it. Mine isn't one of them. Also, the switch is
bulky enough (about the size of a grapefruit) such that I don't want
to have two of them in this rig.

Second, you can
lessen the surge effect by adding a reservoir.

Thought of that, too.... but, like I said, I'm trying to keep the
bulkiness down.

As for leaving your pump running all the time, that depends on your pump
design.

My first try was with a 110V pump taken out of a FoodSaver, and it
would get pretty warm even after about a minute. My second pump, this
spiffy German 24V one (rated to something like .03 atmospheres) runs
much cooler. I might let it go for an hour and see how it does.

A switch
would be better all around instead of running for 24 hours.

Well, I've already designed the circuit and simulated it with a
circuit design program and it looks like it's going to work (and it
only uses about $20 of parts from Radio Shack). I might build it
anyway just for the nerd value. I'm concerned that I'll have enough
leakage into the bag, however, that the pump will end up running most
of the time, anyway.

I am very
interested in your project. How about some photos and more info when you
get it working?

Will do. When I have it working acceptably, I'll post the construction
details on my webpage where I have my home-made T-square fence.

- Joe