Hi
 This is  a very basic question I guess.I have searched a little through the forum,but havent found an answer to my doubt.Sorry if it has already been discussed.
Im starting up with carbonfiber.Have casted some small pieces with different results(learning from mistakes).
But now im focusing my efforts in my vacuum method.
Well,to the point...I though that it was possible to vacuum,stop the pump,and if the bag is correctly sealed,disconnect the pump,and leave the mold in the sealed bag "vacuumed",withou waiting for the resin to gel.
But no matter how I try,when I do this,air comes in again,loosing the vacuum.
The last thing I tried,was creating a home made valve with a "fast connector".As it didnt work,I though there might be a leak in the bag and/or the valve.So,as we always have latex in the studio,and the bag is small(25cm,only for testing,no mold inside),I dipped it a pair of times in latex,to make sure everything was sealed.The result has been the same.
Watching some videos and tutorials,I see everyone till the moment leaves the vacuum pump on till the resin gels.So maybe Im trying to do something that is just not possible?
The main reason for not leaving the pump on all the time is that this is small pump we use here to degass silicones,resins etc...its small,and fairly old,so Id preffer not leaving it on for hours,Im afraid it could "burn".
The resin Im using has a long pot life/curing time.To shorten the time the pump is on,would it be good to switch o a faster cathalyst.
The next step then would be purchasing a new one for this purpose.Could someone help me to know the minimum requisits for a pump used for this?.Also Ive seen there are "venturi effect systems" that will vacuum with a compressor.Is this  a good option?.
I attached an image of the "fast connector valve" I used.Maybe its not the correct kind.I know they sell things for this.But wanted to know what is the problem before.
Right now we are focusing on small parts.
Sorry for my technical english,though born in the US,Ive lived almost all my life in Spain.
Thanks in advance,and sorry if this is too basic.

I don't understand how your valve works, but I'd say that is the issue. I have a valve on my pump, and it works fine. If I leave the valve open then it loses vacuum, which is a given. 

Thanks Henaldo

Its the kind of valve used for air compessors with a fast connector.
Are vacuum valves different from normal air compressor valves?
So then,it is posible to disconnect the bag from the pump once the vacuum is achieved,before the resin gels?.

"If I leave the valve open then it loses vacuum, which is a given. "

Obviously,but its closed in this case,not open.

Ill look for more specific valves then if thats the issue.Though basicly its prevent air from coming in or escaping out,which sounds the same?

Thanks

I'd imagine a pcl valve like that would leak under vacuum as I believe they rely on the pressure behind them to seal, so if there's a vacuum behind it, it would open.

Thanks ajb100,
ok,off to look for it.Ill try clamping the line too.
Thanks!

I know this is a dead thread, but I had a few minutes spare today with the vac pump out and a couple pcl connectors. Hooked up a bit of pipe from the catch pot to the connector and sealed with gum tape

You can also shorten the gel time a lot (specialy now in winter) by using a heater while vacuuming.

At the end,buying a specific valve for this(mold bags),and using a ball tap,has solved my problem.Also as mentioned above,using a short gel time cathalyst,and heat.
Now,if theres a leak,I know its in the bag.Which is the tricky part,I think