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Vacuum Pump

S

StevieB

Nordic Pine
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I have the chance to acquire a small electric vacuum pump. It states on the base that it pulls 1 bar. When I place my finger over the inlet there is suction, but it doesn't feel very strong (although I have no idea how much 1 bar is supposed to feel like). I am wondering if it would be suitable as a vacuum pump for veneering?

A trawl of the interweb suggests most pumps are actually measured in the volume of air they remove in a given time rather than in 'bar'. However there are also a couple of references to veneering pumps being able to pull 25" of Hg. A further trawl reveals that 1 bar is equivalent to 750mm Hg, which would be 29" Hg, indicating that the '1 bar' pump I could get hold of would be sufficient.

So a couple of questions:

Anyone with a veneering pump able to put their over the inlet and tell me if there is light or strong suction?

Anyone able to confirm my calculations above are correct?

I could just acquire it and see if it works, but for various reasons if it's no good I would rather not take it as there are other users who could benefit from it.

Cheers,

Steve
 
Atmospheric pressure is nominally 1 bar (750mm mercury etc)
A pump claiming 1 bar is heading for a perfect vacuum and more than enough for veneering.

The other parameter as you realise is the rate at which it can pump down to max vacuum and this is a function of the pressure difference. It will start off quickly and then slow down as it has to work harder.

Putting a finger over the end won't tell you much other than it is basically working.

You can improve the performance by adding a vacuum accumulator like an empty gas bottle in series with the inlet. Pump that down first. close the valve, attach the bag, start the pump and then open the valve to rapidly take out the air in the bag.

Robert has posted his set up complete with a novel switch to prevent the vacuum pump running unnecessarily.

viewtopic.php?f=26&t=1022

Bob
 
1 bar is roughly atmospheric pressure at sea level so take away 1 bar from atmospheric pressure and you have a full vacuum. I doubt any pump will get to full vacuum but for clamping you don't need it to.

I spent ages looking at vacuum pumps on ebay a few years ago before buying mine.

the volume of air shifted does make a difference to how you use it but it is not easy to get usable figures. It does end up as get one and try it.

if you have a lot of air in the bag when you turn on the pump a low capacity pump will take longer to suck it out before it starts going into vacuum pressures. Also if your bag leaks the pump will not be able to overtake the air leaking in and leaks are not uncommon.

Finger on the inlet will tell you it is working but will not be a strong pull. Atmospheric pressure is 14 pound per square inch so the force on a 1/4" dia inlet pipe will not be that great. Multiply that 10 (assuming the pump can't do better) to 14 pounds on every sq inch by the area you want clamped and it is a lot of force.

pumps sell well on ebay so if its not up to the job there is probably a way out.

Might be worth checking it is continuous use rated as it will be running for a few hours while your glue dries. It bothered me having the pump running all the time so I came up with some extras to store vacuum and switch the pump -

http://www.thewoodhaven2.co.uk/viewtopic.php?f=26&t=1022
 
This is what I bought for mine.

It's got the regulator (that acts the way Roberts one does) built-in.



And this is the basic stuff you need to order.



vacuum bag size to suit whatever it is you are veneering.

Plus the electrical square conduit and dowel to seal the ends and you're good to go.
 
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