Vacuum pump sizing for infusion

Discussion in 'Fiberglass and Composite Boat Building' started by frenette, Apr 15, 2017.

  1. frenette
    Joined: May 2011
    Posts: 21
    Likes: 1, Points: 3, Legacy Rep: 13
    Location: Southern California

    frenette Junior Member

    On the surface of it my pump pulls 28" and should be enough.

    The question is what happens when you open the resin flow then you don't have a perfect seal per the opening in the resin line.

    So who do you account for this opening in the vacuum to pull the resin in? The CFM number is for free flow (per normal benchmarks) of air. How does this get accounted for in real applications?

    I'm looking at this from the standpoint of I've done lots vacuum bagging of small parts and as the size goes up the cups per minute required to fill a larger boat should also go up.
     
  2. Steve W
    Joined: Jul 2004
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    Location: Duluth, Minnesota

    Steve W Senior Member

    You really don't need a large pump to infuse even quite large parts. I attended a workshop a few years ago where we infused half of a hull of a 42 ft catamaran with a small 1/2 hp 6 cfm pump which was meant for evacuating refrigeration gas. I went out and bought the same pump and still use it on occasion but the problem I have found with these cheaper pumps is that they do not like operating under rough vacuum which is what you have if you spend a while dealing with leaks. I replaced it with a very nice German pump which is much larger at around 20 cfm and will run forever under rough vacuum. The smaller pump is quite capable of doing the job though but I don't trust it as it spits oil everywhere. I will still use it sometimes as its so portable but only for VE infusions or bagging where it doesn't need to run as long. I believe in investing in good equipment and a good industrial pump that will run all day is well worthwhile imho.

    Steve.
     
  3. frenette
    Joined: May 2011
    Posts: 21
    Likes: 1, Points: 3, Legacy Rep: 13
    Location: Southern California

    frenette Junior Member

    I'm reviewing my Gast 0823 and it's rated for 26 Hg. So maybe my cheap pool supply gauges have a calibration problem or over the last 10 or they're just broken in.

    I'm looking at this because I want a backup. So I was thinking about a 2 stage evacuation model. I can put the 2 together on the on startup and use the higher vacuum value for the 2 or 3 hours to get it the 36 cat and go back to the Gast pump for curing.

    Thanks for the reply.
     

  4. jorgepease
    Joined: Feb 2012
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    Location: Florida

    jorgepease Senior Member

    ... Infusing with a leak is going to give you more problems than enough vacuum. Besides, possibly not being able to flow the resin, you will continue to pull resin out of the mold even after the lines have been clamped. The opening of the resin line should be part of your vacuum drop test, just clamp off the end of the hose.

    I use a Welch used pump, can't kill those things, I got for 600 bucks on ebay. Very quite, purs along and pulls 30"
     
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