I have a sherline lathe and want to build a venturi vacuum
generator, to be used with an air compressor. This will be
for vacuum bagging composites. Something like this:
Can I just drill a hole in a cylinder lengthwise, and another one
perpendicular to it (or at an angle), drill and tap for the 1/4 NPT
connections and be done, or is there more to it? What kind of
hole diameters work best? Should the holes be tapered?
IMHE, a venturi is the wrong way to make vacuum for vacuum bagging.
A venturi is most efficient when working with a large flow at higher
pressures. It's not the right choice for pumping down to a vacuum (even
when this is merely 1/2 an atmosphere) and when there's negligible flow.
You also need to leave this pump running long term when the resin is
curing, which is annoying with a venturi pump.
IMHO, find a different sort of pump. If the bag is reasonably sealed
then a hand pump or a fridge compressor is perfectly adequate (don't
leave the fridge compressor running permanently though).
"Andy Dingley" (clip) IMHO, find a different sort of pump. (clip)
I agree with Andy. A great many woodturners use vacuum chucks, so the
question of what is the best pump has been thoroughly discussed. These jet
pumps require a large compressor. The compressor plus the pump is noisy and
inefficient. Better to use a Gast vane pump or a compressor from an old
refrigerator. It is also possible to adapt an automotive air conditioning
A pump that works really well for vacuum bagging, well my opinion anyways
and what I use is a surge vacuum pump for milking cows, and you can leave it
on for as many ours as you need, they work awesome.
You can pretty much find them in like a milking supply company or a
local farmer, might have just sittin around since nobody uses the surge
vacuum pump for milking anymore they use a rotary pump nowadays, and every
old farmer that milks has one laying around its a given! Good Luck
I did all my vacuum bagging of hull and rudders using a 2 stage Gast vacuum
generator. I have no idea how to build one. I originally thought it was
a cheap way to have a vacuum pump. By the time I assembled the whole
contraption, "I could have had a V8".
Here's a pic:
To minimize cycling of your compressor, you really need to incorporate a
vacuum reservoir which means you need a tank, hi-flow check valve, gauge,
vacuum switch, and solenoid valve. Basically the way it works is that you
create vacuum in a tank and when you get to the desired vacuum, the solenoid
valve shuts off the line to the air compressor. The check valve is so you
don't loose the vacuum. As your vacuum bag inevitably leaks, the volume of
the tank is enough to compensate and keep the vacuum. Eventually the
vacuum drops below a specified level and then the vacuum air hose kicks in
again. With the exception of when the air compressor runs, and when the
vacuum generator runs, the system is completely silent. That makes it real
easy to find leaks.
If I were to do it again ... I'd probably get a vane vacuum pump with good
volume. Check out eBay.
No, a Hilsch tube is a completely different animal.
A Hilsch tube takes compressed air in the middle and gives a stream
of hot air out one end and a stream of cold air out the other.
No vacuum involved.
Jim Wygralak Public key at
OpenPGP (gpg) signed messages get a free ride past my spam filters.
Bumperstickers for your coffee cup:
BTW: When I did my hull I had a well sealed bag. As I recall, the
generator ran about every 15 minutes and my 30gal compressor ran about every
50 minutes. Depending on how well your bag is sealed, your mileage may
vary. I used construction adhesive for my bag sealant.