vacuum pump size

[Herman]

I've had a Welch as well, a 1396 I believe. I swapped it for a smaller, contained pump, as the Welch was simply too large.

I do remember however the sign on the motor:

"please lubricate every 10 years"

I guess they don't make them like that anymore...

However, the Robinair pumps switching off surprises me. Are they produced for 100% workload? Or perhaps 50%? any pump used for composite work should be able to do 100% workload (or: 24/7 running). This should not harm the pump.

The trolleys I produce however have a vacuum-regulator, which switches off the pump when the desired vacuum level has been reached. This way you can trace leaks, the pump does not run all the time (energy bill!) and if the pump starts running more often, it is time to check the workpiece.

Vacuum pumps can get hot. In celcius, a temperature of 80 degrees C is normal. Although you cannot touch the pump housing anymore, the pump has no parts that are harmed at that temperature. (it is all steel, bronze and some seals and gaskets)

[ahender]

Thanks for all the great comments.

I am looking at Thomas and Gast vacuum pumps at grainger.com.

My budget is ~$800.

Gast has a 1 hp, 13 cfm, Hg 25" model for $844.

Thomas has a 1/2 hp, 4 cfm, Hg 27.9" model for $661.

These are all oil less pumps.

I'll be pulling the vacuum on a 13' canoe mold.

Since there is not a lot of air to evacuate am I better off with the Thomas pump since it has a higher vacuum rating or is horsepower always the better bet?

thanks....alan

[Herman]

How much vacuum do you want? Probably not the "full pull" from either pump. Why not invest in a smaller pump, and a vacuum switch? Makes things much more civilised and controllable.

[KnottyBuoyz]

Plenty of Gast vacuum pumps on e-Bay in the $200 range.

http://shop.ebay.ca/?_from=R40&_trks...All-Categories

[AndrewK]

Alan,
I agree with Rick, if you are not a professional builder then a cheaper second hand pump makes more sense.
The type and capacity of the pump depends on your requirements.
If you only plan to vacuum bag a canoe then a small diaphragm pump would be my choice. Most diaphragm pumps will only achieve 80-90% vacuum but can be run at any level and usually have a built in bleed valve to regulate this.
Oil pumps have higher vacuum but generally are designed to run at full vacuum only, this is what you need for infusion work.

Andrew

[ahender]

What would be your definition of "small?"

1/4 hp, 1/3 hp, 1/5 hp?

thanks...alan

[AndrewK]

Alan,

I have been fortunate to have been able to borrow a number of vacuum pumps from my ex employer (lab).
I use a 200w(1/4HP) diaphragm pump for vacuum bagging, it reaches 80% vacuum and has only small volume capacity that may only be around 2L min but I have not measured it. I have made all of the bulkheads for my 12m catamaran using this, also flat panels up to 3 x 1.5m.
I have two oil pumps that I use for infusion a small 250W one that reaches 96% vacuum and once again only 2-3L min capacity, I have infused 6 x 2.5m laminates with this.
The larger oil pump is still only 1/2HP twin stage almost 100% vacuum and once again only guessing 5-10L min capacity. This easily does half a 12m hull.

I am not saying that volumetric capacity is not nice to have just that its not worth paying the extra money unless you are a professional. It is easy enough to draw down large volume bags initially with a vacuum cleaner.
The essential thing is that what ever type of pump you get it is designed to run 24hr.

From my experience most labs will have a old disused pump gathering dust in their store, do some ringing around you may end up with one for nothing.

Andrew

[sigurd]

do you put epoxy on the corecell before you infuse it?

[AndrewK]

No you assemble everything dry and only mix and introduce your resin after you have determined that there are no leaks in the bag.

[ahender]

How many layers of cloth are you infusing?

alan

[Wynand N]

Originally Posted by Herman

How much vacuum do you want? Probably not the "full pull" from either pump. Why not invest in a smaller pump, and a vacuum switch? Makes things much more civilised and controllable.

somewhere is a thread with photos where I made an experiment with two vacuum pumps pulling two identical areas with the same layup. One panel only had a 6cfm pump connected, the other panel a pump of similar rating and connected with that pump, a cylinder with about 115lt of vacuum. When the pumps reached an identical vacuum, -87kpa at my altitude, the resin feeds were open. The cylinder with (stored) vacuum was open with the one pump, sucking the same line.
In theory the pump with the vacuum "boost" cylinder should infuse faster but the result showed such a little difference it can be ignored.

Best listen to chaps and go for a good smaller pump and that should do the job.

[sigurd]

alan are you asking me? for the hull only two light ones, for the fin it will be thick - 2-3mm or more.

[ahender]

Actually I was asking Andrew.


alan

[jim lee]

ahender

We use this one.

McMaster-carr www.mcmaster.com PN 4396K45

It pulls between 29" & 30" HG an goes for : $726.91

For a smaller boat like what your are doing, it would be my pump of choice.

-jim lee

[AndrewK]

Alan,
Its a foam sandwich so the laminates are relatively light, 450 - 1200g sm.
I have done a solid glass test block for the flange of the mast connecting beam, this was 24 x 450g UD + 4 x 450g DB. This worked out flawless; no bubbles & translucent, the only thing you can see is the stitching thread. I hope the real ones work out just as well when time comes.