vacuum pump size

[ahender]

Andrew:

When you infuse all the materials at once, do you worry that some areas may end up dry?

What do you see or not see that would indicate everything infused properly?

alan

[AndrewK]

Alan, with glass reinforcement it is very easy to see dry spots, these will stay white while the resined fibers will go translucent. If this happens and you end up with a dry island spot all you do is attach a vacuum line to the bag on top of this spot. This will draw the resin into the area, once it goes clear you can clamp this line. Of course you can only see what is happening on top of a core, you can not be sure that the bottom laminate is OK until you de-mould. But in my experience providing your core has sufficient perforations if the top laminate is OK so will be the bottom.

Also I do not infuse everything, most of my catamaran bulkheads especially if they have cutouts in them I have vacuum bagged.

Andrew

[13AL]

Wow, great info. After reading the thread, I was wondering if you Pro's have a formula for square footage or cubic footage per cfm of vacuume required. I realize this may be hard to determine due to the laminate count but a "rule of thumb" would be helpful.

[KnottyBuoyz]

Originally Posted by 13AL

Wow, great info. After reading the thread, I was wondering if you Pro's have a formula for square footage or cubic footage per cfm of vacuume required. I realize this may be hard to determine due to the laminate count but a "rule of thumb" would be helpful.

Not sure what you mean. A rule to determine vacuum pump size based on the square footage of a layed up panel?

I think the point we tried to get across is a vacuum is a vacuum and the volumetric capacity of the pump has little to do with that. A larger (volumetric) pump can remove more air from a laid up part. A smaller pump will do the same job just takes longer. If it's a really big part use a shop vac to get rid of most of the air volume in the lay up then switch to your regular vacuum pump.

I use the same pump for a 1 sq. ft. part as I plan to use on the infusion on my 31' trawler hull.

[AndrewK]

13AL
I am no pro, but basically even the small pumps out in the market can do reasonably large jobs, big capacity is nice to have but not essential.
I don't know what the pros would say but for a very small pump if you only used 1/2 the volumetric capacity to suck the resin in and the other half in reserve to chase up any minor leaks that may develop during infusion without losing pressure seems like a good starting point.
Say you had a 10x2m panel and 1mm stitched glass laminates either side of a core.
10mx2mx1mm=20L x 2 =40L and with a full vacuum your glass volume fraction for stitched reinforcement will be approx 50%. This means that out of the above 40L the void to be filled by resin is 20L. Add say 0.5Lm2 for the transfer medium and plumbing this makes 30L total resin requirement for the job.
Personally I would be happy to take 30 minutes to infuse such a panel, this makes 1L/min of resin plus 1L/min spare capacity, so the total volumetric capacity of the pump required is 2L/min.
How does this sound?
Sorry US guys you will have to do your own conversions, metric is so much easier.

[13AL]

Gentlemen, thanks for the replys. That cleared things up a bit. Our main concern was having a pump(s) too small and running the life out of it. We found a 5 hp near by that looks promising and considering installing a system like Rick built. I'm sure the 5hp will be overkill but the price is right. AndrewK, thats some good stuff right there. The more info like that we can get the less costly the mistakes will be. Dan.

[AndrewK]

13AL
Make sure the big pump is a high vacuum pump. Once you have exceeded the minimum capacity you require I would rather have a small 99.9% vacuum pump than a large one at 95%.
Automatic switching such as Rick's would be nice especially since it is 5hp. Just make sure the cycle range is small, say2%?

[13AL]

We had taken that into consideration (99.9%) and will be running it this weekend to find out just that. I am guessing here, but our goal is 29.9-30in ? The only draw back to Rick's system is cycling our large motor a bunch. Sometimes it's lighter on the power bill to let a large motor run rather than start stop. Then again, It's only money. I'll just make more. In case our big pump is'nt so big after all, we were viewing E-bay and had noticed what seemed to be some pretty good buys, however we could not find the vacuum ratings which made us a bit apprehencive. These particular pumps were Alcatels and Sargents. They look to be a vein style? Any info about these? or should we keep looking. Thanks, Dan.

[KnottyBuoyz]

Originally Posted by 13AL

The only draw back to Rick's system is cycling our large motor a bunch.

The relay that controls the pump can handle 30 amps. That should start pretty much any motor up to 3 or 4 HP. Your pump should have it's start/surge amperage draw on the mfgr's label. I know the Robinairs don't. I originally had the 10 Amp relay installed and fried it. IIRC my Robinair is 1/3 HP.

[13AL]

Rick, Thanks for the heads up. Will the Robinair produce 30" vac?

[KnottyBuoyz]

Originally Posted by 13AL

Rick, Thanks for the heads up. Will the Robinair produce 30" vac?

Damn near! Near enough anyways. I've got the regulator set to shut off at 28 and back on at 26. I have bottomed out the vac guage (30" hypothetical) w/o the regulator. These are uncalibrated readings though. I don't have the equipment to verify if they're actuals.

What I've found with my experiments is that the 26-28" range works best. I've come up with a few "dry" layups under very high vacuum where I've literally sucked the resin out of the layup or the overlying materials, peelply, flow media & bag have so compressed the layup that it couldn't absorb any resin.

So I guess, and others may confirm this, that achieving 30" of vacuum isn't really "the" most critical specification for a vacuum pump. Duty cycle is probably more critical and we've talked about that.

I think it was Wynand with his experiments showed the benefit of having a large vacuum reservoir when infusing larger panels. Mine is about 1.5 cu ft in size. I draw that down to 28" keeping clamped off from the layup until I'm ready to infuse. Bringing the layup under vacuum quickly seems to help eliminate some creases and bridging. Just an observation.

[13AL]

Update: Tested out large vac pump with poor results. 16" was all it would give. Lucky for us all we had in it was some labor. Now it's off to Graingers for a pair of 1.5 hp pumps. I kinda had a feeling we were going to end up here. Not to jack the thread but.... has anyone had any kind of luck infusing past 90deg. in a mold or will the bag, ply, cloth, resin just drop away from the mold. Thanks, Dan.

[KnottyBuoyz]

Originally Posted by 13AL

Update: Tested out large vac pump with poor results. 16" was all it would give. Lucky for us all we had in it was some labor. Now it's off to Graingers for a pair of 1.5 hp pumps. I kinda had a feeling we were going to end up here. Not to jack the thread but.... has anyone had any kind of luck infusing past 90deg. in a mold or will the bag, ply, cloth, resin just drop away from the mold. Thanks, Dan.

I've read somewhere, can't put my finger on it at the moment, but it was a guy infusing the tumblehome stern on a boat (upright) and it worked no problem, you get the same compressive force from the vacuum at any inclination. So in short, it shouldn't fall away. Laying it all up though, that's a different matter. Might want to get a can of 3M Super 77!!!!

[jim lee]

Bagging at odd angles should be fine. Spraytac the stuff together. I wonder at the 1.5 HP pumps. If you have no leaks, I can't understand why you need such a large pump. If you -do- have leaks, we've found that they cause all sorts of trouble in your laminate.

-jim lee

[13AL]

Jim, our thinking as far as the 1.5hp was the long haul. The price was not that much more. "Bigger is better" sort of? Just a thought. Rick, Thanks for the advice. we're looking forward to giving it a shot. Dan.