If I understand the procedure correctly, vacuum machines run continuously to maintain vaccum while curing. However, I am curious to know if one can create the vacuum, clamp off the hose, and then disconnect the vacuum.
Can this be done? If not, why not?
Yes, of course but vacuum should be “perfect”, and even then everything has some level of permability so you will start to slowly loose vacuum overtime. Generally its just best to run the vacuum pump just to be safe…
Also, you could have a perfect bag and have air trapped in a bridge or between plies. Having the vacuum on throughout the cure makes it the more likely for any air to escape, especially if you involve heat. That’s why I always debulk depending on complexity. Often Ill have a perfect bag and about 3 hours into the debulk I hear a thump and the bag creases as a bridge gets consolidated.
I don’t have to much experiencie with infusion, but in my little opinion if you have no leaks and a tank with some vacuum reserve you can turn off your vac pump. I use to check it for around one hour and if is ok leave it there to cure, and next day I can losse between nothing to 3inhg. My vac pump use to get really hot, thats why I like to do it this way.
vacuum switch. Maybe costs 100 $, but your pump wont run as long 
especially with a buffer tank. And it’s adjustable
I rarely had bags which hold their vacuum long enough for a whole cure.
(and my pump leaks a tiny little bit… and yes Herman, checked the valves, all clean )
If you need to transfer a part to an oven, yes you can clamp the line and move it. But you need to reattach the vacuum. Reservoirs can be used, the bigger the better, but in the end, any loss of vacuum, still equates to a loss of vacuum, even with a 5 gallon buffer tank. It’ll be much slower, but the same. If your pump is bad, and mists, or over heats, try the switch, and try a small on-off setting, just to keep the pump from blowing up
Thanks for all the replies.
Also you have to be careful just switching the pump off while its attached to the bag. You have to disconnect or use a valve. If its a good bag, when you switch it off, it will suck the pump oil from the pump back into the bag, as the negative pressure in the bag is quite powerful. This happened to me twice now. First time I thought it was because my pump was on top of the oven. Second time it was on a timer to switch off along with the oven, the pump was under the oven this time, it still sucked the oil up.
Thanks for the heads up on suck back. I am inclined to try to seal the bags and disconnect. Something seems not quite right with leaving a machine running to maintain vacuum. My intuition tells me a perfectly sealed bag should be able to maintain vacuum to within one inch for the relatively short 24 hours required to cure. I’ll report back on results.
See the black thingy next to the meter? It is a shut off valve. This isolates the pump from the vacuum line, while not running.
(picture from www.vacuumsystemen.com)
The ultra-ultra cheap pumps do not have this valve. A simple non return valve should do the job. By far most Industrial pumps have nrvs built in.
One of my customers built his own vacuum system, fromparts he had lying around. This included a switch, and a buffer tank. Use what you have, so the buffer tank is some 2200 gallon (8000 liters)
What kind of switch? Timer, preostato?. I had thought about that solutions, particulary in the preostato. But another think why I like to stop the vac pump is because it dosen’t suck out any more resin, driyng the part, even through the break zone, the presure gets equal in the hole part. I never had any problem with oil geting out the pump, but just in case I’ll check it out with the maker.
Timers are useless. Use a pressostate.
Whether or not the pump is running, the vacuum will suck resin out. It depends on your leaks and/or setup if you get voids.
Pressostate which is useful from ambient to 100 mbar abs (-0,9) is this one:
http://www.vacuumsystemen.com/toebehoren/vacuumschakelaars/vacuumschakelaar.html