I achieve the same thing with a ball valve as a bleeder, but my pump is huge and needs quite a big 'leak' anyway.
but just a thought cos any valve jusst cracked open may do it for you

I used a MAP sensor connected to a voltage dependent switch. It works great, which means I should find a backup for it in case it breaks one day. In fact, I should use an Arduino connected to it to allow a bit more intelligence.

If none of this makes sense to any of you, don't worry, just ignore it

Refrigeration compressors are designed to run at higher than ambient suction pressure if they run for any length of time in a vacuum they will spit their oil out and eventually fail. I have no experience with vacuum bags but refrig mechanic by trade. Switching compressor off rather than bleeding vacuum sounds a safer way to go. Best of luck.

snoopySA said..
Refrigeration compressors are designed to run at higher than ambient suction pressure if they run for any length of time in a vacuum they will spit their oil out and eventually fail. I have no experience with vacuum bags but refrig mechanic by trade. Switching compressor off rather than bleeding vacuum sounds a safer way to go. Best of luck.

Thanks snoopy, though I would have thought the valve that I mentioned would allow air into the compressor when set to less than a vacuum, and additional valve might solve that problem.

The company that sells the vacuum sells these pumps, on ebay, they seem to be sold a fridge pumps.
www.ecfibreglasssupplies.co.uk/product/vacuum-pump-s-cc-31

Once I worked out what I wanted I am hoping to pick up it all second hand, though.

jonesmb said..
Actually I use Arduino connected to pressure transducer to switch on and off the pump, depending on vacuum level. This approach means the pump runs for a few minutes every hour, provided the bag is well sealed. More info here files.acrobat.com/a/preview/4b9a222b-470b-437f-bdb4-892a16680537

When I was using fridge compressors I made sure I had a back up ready to go if it failed.

Thanks for the link, competent with a soldering iron, just want to avoid wreckers and driving all over the place, and don't want to spend a motza.

I will have a rethink now...

Just read the date on your link 'hot off the press'

snoopySA said..
The link is a vacuum pump specifically designed for pulling vacuum. We use these to suck out systems before adding refrigerant. You won't have any problems with this type of pump it will pull 30 Mercury inch vacuum but just would need to be regulated. Thought you were referring to compressor pulled out of fridge. I have an old two stage vac pump you can have however it is heavy(20 or so kg) you might find second hand on gumtree.

Thanks again!

There are lots of those on ebay at more sensible prices, they refer to them as Refrigeration pumps but I get the connection now.

160 bucks for this one.
http://www.ebay.com.au/itm/66-L-Min-two-Stage-Rotary-Vane-Vacuum-Pump-Refrigeration-/322240761169?hash=item4b070bcd51:g:mCUAAOSw3mpXKVkp