----- Original Message ----- From: "Al Scidmore" <[EMAIL PROTECTED]>
but my pump occasionally has a problem restarting against vacuum
If you have a continuous duty pump and you run it continuosly then restarting is not an issue. If you use a system that has a reservoir and a vacuum switch such that the pump cycles on and off then restarting the pump against a vacuum is an issue. In that case you simply need a check valve between the pump and the vacuum switch. You then put a small bleed hole in the vacuum line between the check valve and the pump so that the vacuum in the line immediately adjacent to the pump bleeds off while the vacuum in the system is maintained (check valve prevents air from flowing towards the pump and escaping from the small bleed hole). This way the pump will not have to start against a vacuum.
Do you use bag clips on both ends of the tube?
Yes, both ends of the bag are sealed with clips. I don't use the messy caulking type sealant stuff.
My system is not completely tight. If the pump turns off then the vacuum is lost within a few seconds. I don't know where in the system the leaks are, the pump itself may leak since it is old and has run for many hundreds of hours. My pump just runs continuously. Vacuum is regulated with a bleed valve. You just set the bleed valve such that the rate at which air bleeds from the system matches the flow rate of the pump. This happens at a different vacuum level depending on how much total leakage there is in the system. Total leakage depends on random leaks plus the bleed valve leak rate. Small leaks in the system don't matter as long as the pump can keep up. The real limiting factor to leaks in the system is due to the fact that vacuum levels will vary in the system. You will have less vacuum near the leaks and more vacuum away from leaks. Eventually this vacuum differential forces you to have either too little vacuum in some parts of the system or too much vacuum in other parts of the system. I typically run between six and twelve bags at a time. When I start to see signs of low vacuum coming from some of the bags I will either investigate to determine which bags are leaking too much and replace those or I will just change all of the bags at once. Signs of low vacuum would be when I see that the mylars were not sucked down as tightly arouind the LE of the part as usual or if there is not the usual amount of resin oozing from the part. A sign of too much system leakage would be that my bleed valve is almost completely closed to get the desired vacuum level on the gauge.
Most of the above is of no importance to the casual vacuum bagger. The real point is that you can set up a simple system with a continuous duty pump and the bag supplie I have described. You can just use a bleed valve ti regulate vacuum level. This system does not require the use of a vacuum switch or reservoir and does not need a completely tight and well sealed system.
Pictures of my system can be found here;
http://www.rcgroups.com/forums/showthread.php?t=333843
Phil Barnes wrote:
----- Original Message ----- From: "Al Scidmore" <[EMAIL PROTECTED]>
How do you create a never-fail bag?
Bag tube, bag seal clips and bag nipples from CST. Continuius duty Gast pump. Small leaks don't matter if you use a continuous duty pump and let it run for the entire cure cycle.
Phil
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