Vacuum Pump Suggestions

Wet bagging: Hand laminating, then laying up vacuum materials (usually peelply, bleederfilm, breather, bag), then applying a vacuum.

Resin infusion: Dry layup of fabric, laying up infusion materials (usually peelply, bleederfilm, transport medium, bag), then applying vacuum, and when all is OK, mix resin and "suck it in".

About pumps:
Rotary vane pumps are OK. They do wear, but when treated nicely, last a very long time. it is usually the mis-used pumps that have problems. Running the wrong direction is disastrous. Always keep an eye on that.
When you master the process of applying bags that are (almost) free of leaks, a small pump will do. When the bag is almost closed, take a vacuum cleaner, put the hose in the bag, and turn it on. It evacuates air much faster than a vacuum pump. They just do not like running without air moving (the air cools the motor) so do not overdo it. I sometimes even attach them to the resin inlet (resin infusion) and seal the connection with my hand. sounds silly, but works OK and very fast.
Oil lubricated rotary vane pumps should not run for more than 10 minutes out of specs. (usually they should develop 500 mbar abs or less). This is to prevent them spitting oil. On the outlet there is a filter, which catches the oil. This filter is a cotton-like material, where the oil condensates, and drips down. The generated vacuum moves the oil back into the pump. If there is no vacuum, the filter overloads with oil, and then needs replacement.

About wet bagging:
Make sure you laminate the first layer relatively resin rich. When applying a vacuum, the excess resin moves out through the laminate, and takes the residual are with it.
A good laminate is a bit of experimenting with vacuum level and used bleeder film. A P3 perforation and 300 mbar abs pressure (-0,7 bar as you wish) is a good start.

About peeplply:
Actually, the term "peelply" is a bit confusing. Actually, I use perforated film (bleeder film) to peel the rest of the materials of the product, as this is MUCH easier. The peelply is left behind to protect the laminate against traffic (in boat hulls), resin spills, etc. Peelply is only used when a coarse surface is needed, or when protection during building is needed. Many products can do without.

About vacuum pumps and resin infusion:
I prefer a pump with a pressure switch. This switch will keep the vacuum between certain (user adjustable) vacuum levels. This way the pump only runs when needed. Better for the environment (who cares?), my energy bill (I care!) and best of all, the interval between the pump running is a measure for the amount of leakage you have. If the pump suddenly runs more often, it is time to check the part.
I use Danfoss RT 121 pressure switches, hooked to a magnetich switch (relais) which switches the pump. The hysterese of the RT 121 can be set between 100 mbar and 10 mbar, the latter is OK. My customers however reported that 3 mbar hysterese is possible.

Also it is easier to hear leaks, as the pump is not constantly running. And my experience with needle valves is that it is hard to keep a constant vacuum.

Good luck choosing a pump!

 

Thanks members for the advice.

Seems there was a little confusion in this thread about wet layup vs. infusion.

Infusion seems great -- not having to rush to get everything laid down and bagged and sucked down prior to the resin kicking. Not sure how practical it is for the one off or the back yard builder. Though Derek Kelsall says it is well within the reach for the skilled amateur. He is using infused panels to build his catamarans. I may try it once my shop is finished. My goal is composite panels and then a hull from the panels -- I know, no compound curves.

An interesting quote from Peter Hledin of Skater poweboats fame:
Why he doesn't infuse:
"We've tried the process several times and found that although it can be a benefit for many boatbuilders, the laminate is 20% heavier than ours due to the high resin saturation of core material"
Professional Boatbuilder Magazine no. 109

I think his core of choice is end grain balsa.

Anyway, this is a great forum and I've learned a lot from it.

James Mills

 

I have a small project I'd like to try the infusion on before I tackle the big stuff. I like the idea of preparing everything and holding off the resin till everything is ready.

I think I must make myself a resin mixer too.

The vacuum bagging sounds like it's still a lot of work.

 

From what I understand an important consideration for the amateur builder is the risk of ruining the part. Hence trying on smaller parts is important to build up some basic level of experience.

If I were to infuse a part I would post some pictures of my preparation steps to give the experts here a chance to guide me as I go and to point me to the mistakes I will inevitably make

My job is totally unrelated to boatbuilding, but one major lesson I have learned which applies in any field, is that if there are experienced people around willing to share their expertise, than use that resource in any way you can. (And never think you know better )

 

Infusion is suitable for both production builders and DIY boatbuilders. I have several clients that build just one boat, have no experience in laminating, but do a great job infusing a part, or complete boat hulls. There is this one guy, who did a 50 ft boat, WITHOUT any hands-on help. (he did use some advice, though).

Do some test, look at pictures, get some help from a knowledgable person, and there you have 80% of the job. The other 20% is experience. Try and help or witness an infusion before you try your own, and that surely helps.

Furthermore, and very important:

Infusion is very much dependant on leakage. The more leakage, the more experience is needed to infuse a good part. I have done some infusions on pretty leaky undergrounds / bases, but I like a complete airtight setup more. Much less hassle during infusion. Testing your base for airtightness is a step that is skipped many times, but is very important. It is a simple task, and generates some experience in closing a vacuum bag, which can be a pig the first time you do that.

 

Vacuum pump

Hi

Here in France we very often use a fridge compressor as a vaccuum pump and an engine depression capsule to regulate.
Cost nothing
Work great

 

Robinair 15600 New 6 CFM A/C Vacuum Pump HVAC

I am getting ready to host a Derek Kelsall KSS workshop. I am looking at purchasing this pump, the Robnair 15600 6 CFM. I am wondering if it has the switches like Hermann is speaking of and if I can tie the RT 121 into this system, does anyone know.

**EDIT: Ok I found this link answering my question http://www.boatdesign.net/forums/showthread.php?t=20419

Thanks,

Pat Ross