vacuum pump

[miniscool]

Hello all,

I need a new vacuum pump and would like to learn from your experiences in order to make the best choice.
What sort of pumps do you use, what can you suggest me ?

[Jeff Therrell]

What are you using the pump for? We use a 1 hp busch pump for our infusion opperations. I have 2 pumps setup on a 80 gallon reserve tank. I rarley use both pumps at the same time but I have a spare if something happens to the primary one.

[miniscool]

pump wil be use to put vacuum after having carbon fiber 'wet' laminated with epoxy. But I want to start some infusion also and need a pump able to manage it.

thanks

[yokebutt]

Mini,

Ideally you'd want a pump that can pull at least close to a full vacuum, I use a 3/4 hp rotary-vane one from Dayton. That's been big enough to bag hull and deck parts for a 31 footer.

For big bags I use a "bulk evacuator", it's just a 1 1/2" plastic thru-hull fitting with a plastic ball-valve that hooks up to a large vacuum cleaner. It gets the bag down quickly and gives a little bit of traction so I can shift the bag material around to where I want it, then I let the pump take over.

Yoke.

[zerogara]

I've been told by others that AC/refrigeration compressors can be used and although I haven't tried it I suspect their are durability issues.
Most AC compressors incorporate some form of lubricant for keeping it cool enough so it does not seize. It will be hard to do this in creating vacuum since there is not much flow of gas through it to drag some lubricant through.
On the other hand you need continuous operation where most refirgeration compressors run for a short period of time and stop once a temperature switch shuts them off. This gives them time to cool off a bit before the next cycle.
I have some 30+ year old GE AC units that still pump ice cold air. If I could find someone to store the R12 in a tank for me I'd try it.

[Buckle]

There are two main types of vacuum pumps commerical available. The first are the cheaper standard, dry rotary vane pump. These run dry (no oil) and typically pump down to 100-125 mbar (absolute). They can run continiously and typically need surfacing after 4000hours running. You can purchase these for a few hundred pounds. They are excellent value for money. They
are great at pumping high volumeteric flowrates of air, but struggle down the lower end of the vacuum spectum (<125mbar).

Oil rotary vane pumps are much more expensive than dry rotary vane pumps. As a result will pump down to 0 mbar - the perfect vacuum. Unifortunitaely these pumps are 10 times the cost compared to their dry running counterparts, and need regular servicing (around 500hrs max I believe). These pumps love working down the lower end of the vacuum spectum. They dont like being used to pump hight volume flowrates for prolonged periods of time.

The type of pump you require depends on your application. For infusion and prepreg-ing I perfer oil filled pumps any day. Althought cheap and cheerful vacuum cleaners can pump 500mbar, so they are great for displacing large amounts of air from your initial vacuum bag, althought i have never infused using a vacuum cleaner. I will give it a go one day.

Commerically it makes sence to use oil filled rotary vane pumps. When working down the <100mbar vacuum range, its better not to over work you pumps. We have recently installed a vacuum ring-main, consisting of two oil filled rotary vane pumps. Two pumps are used just in case one pump dies during the process. Both pumps operate at the initial pulling down stage, then during the infusion, one pump is used.

Ignoring the layup time, the cost of materials and labour for our larger infusions is around the £60-80k mark. As a result, the ring-main has its own emergency generator just in case of a power cut. This kicks in automatically to minimising a totally f*ck up. Hope this advice is useful. Let me know yo decision.

[nassaw]

I ended up building my own. I had a electric motor kicking around so I went to a junk yard and picked up a Delco Remy AC compressor from an old Caddy. Older model so It was free. Took the clutch assembly off and replaced with a 6" sheave. Used a fan belt and I had a very reliable pump. I haven't tried it for infusion yet but with the help of a shop vac I bagged several 40' + bags and have since completed a 40' catamaran. The shop vac trick is great for removing large amounts of air from large pulls. The real trick is to build a good air maifold to hook to each bag so different hook ups are available and if you use a shop vac. The ones with the seperate cooling fan for the motor. Most vacs use the air being sucked to cool the motor and when the bag is completly deflated there is a chance for the motor to overheat and shut down or atleast shorten the life of the motor.
What ever you decide. Like other post have mentioned. Reliability is Key after you throw all that money into a vacuum Bag.
Good Luck
Bob C.

[fhrussell]

You'll want to find a 2-stage pump for 0 mbar (absolute) pressure. A single stage will do it (depending on the size of the part).

[zerogara]

How dense does a foam core have to be not to be affected by pressure?
Can a laminating surface pressurize it to deflect enough that when pressure is removed it could force delamination?
I can understand that for infusion you need all the vacuum you can get to assure distribution of resin, but for simple vacuum bagging of core material I think 1 atm. of pressure is extreme. If it doesn't bond at 0.85 chances are that it will not.
Just wondering. I've vacuumed small parts only.

[Buckle]

I think the answer depends on the type of foam you have? Cheap and cheerful pu foam wont stand up to much. I know 40kg/m3 doesnt like 1 bar. Corners etc deform. However a structural foam like pvc will withstand greater pressures (negative). I have happenly infused components with H60 grade pvc (60kg/m3). I image you could drop down a great or two.

The DIAB webpage will be able to tell you. They wont make an infusion core unless its totally stable for high vacuum.

Vacuum bagging doesnt really matter. Any vacuum will increase it properties. I think the vacuum level depends on numerious factors such as,

size of moulding.
no. and skill of labour force
gel time
whats practical? (500mbar is easy to achieve with little effort. <100mbar requires a much great time and skill on complex shapes).

We vac bag our core to ensure a unform bond at 500mbar +/-50mbar. Although this technique adds time to the process, its reduces cost elsewhere in the process.

[bazza]

dont know if these are of any interest
http://www.surpluscenter.com/item.as...&catname=water

[bilgeboy]

Any experience with the "venturi" pumps? I've got the compressor already, and they are real cheap.

That is a cheap pump linked above, wonder if its strong enough at 1/3 of a pony.

Mike

[Buckle]

Plastect TT manufacture a wonderful venturi vacuum pump, designed for rtm-lite applications. Works wonderfully, but not sure how it would rate on large vac bagging applications.

I imagine they arent as efficient as electric pumps thou. However nice and safe for use in highly explosive areas where non-sealed electric motors cant be used.

[zerogara]

Originally Posted by bilgeboy

Any experience with the "venturi" pumps? I've got the compressor already, and they are real cheap.

That is a cheap pump linked above, wonder if its strong enough at 1/3 of a pony.

Mike

I think that the pump above is great for deflating the bag initially before the real vacuum pump takes over. Those pumps move volume but do not do much in lowering pressure IMHO.
It is short of comparing a compressor with one of those pumps that are used to inflate mattresses and inflatable children's toys.
Yes it seems pretty cheap but how many don't have a wet/dry barrel vacuum cleaner in their shop?

[marshmat]

Have a few in the shop right now... an old Cenco (I think, the label's kind of worn) that dates back to the '50s (?) is my favourite. There's been enough advice already on oil-vs-dry and the utility of a shop vac.... my tips: keep the oil full and clean, check the belt a lot, it's good to use them in pairs on different plugs (if one loses a vane or a belt, or a circuit breaker goes, your part still survives). I'd use two small pumps over one big one, but cost is of course a factor there. Whatever you buy, a must-have is some sort of separator or resin trap in the vacuum line- nothing worse than getting epoxy in the pump itself. And pick up a $10 garden hose to vent it to outdoors, else your shop will stink to high heaven.