Vacuum Pump

[dmidkiff]

I have found a used Robinair vacuum pump for sale near me. Can't see model # or CFM output. I have looked at new and they range from 1.5CFM to 10CFM. The prices start at $139.95. My question for anyone that wants to reply is--
What is the lowest CFM you would want for vacuum pucks and/or vacuum bagging?
Thanks in advance, Dave

[ssflyer]

For pucks or bagging, the CFM makes little to no difference - only the time it takes to suck any air out. The more important spec for your application would be "Hg or what it can actually pull.

[Burkhardt]

For pucks or bagging, the CFM makes little to no difference - only the time it takes to suck any air out. The more important spec for your application would be "Hg or what it can actually pull.

I agree only partly. Even with a smaller puck you will have some leakage around the gaskets or through the work piece porosity. I am using one of the 4 cfm GAST pumps that are selling refurbished on eBay for about $150 and that is about as low as I want to have. In a perfect situation my pump pulls about 25" but very often that drops to 15 or 20". Actually I just bought another one to run in parallel and have a little more reserve for porous or uneven material. For what it is worth I have a 6 gallon reservoir (which is ample to get the initial suction) and it takes about 15 to 20 seconds to pump it down to usable vacuum. No big deal.

[Ger21]

If you get rid of the 6 gal reservoir, you might find that you get more suction.
Without the reservoir, the vacuum only has to suck the small amount of air in the lines and puck (pod). With the reservoir, it has to evacuate 6 gal of air.

[coryatjohn]

>> With the reservoir, it has to evacuate 6 gal of air.

Unless you pump the reservoir down first!

[Burkhardt]

>> With the reservoir, it has to evacuate 6 gal of air.

Unless you pump the reservoir down first!

Absolutely, that is the whole idea. If the pod seals well from laying the work piece on it you don't need a reservoir. But usually there are gaps and you would need to push down manually to seal before the vacuum becomes effective.

With the reservoir you can allow for minor gaps. I keep it evacuated as long as the machine is turned on and just open the valve to the pod. It will suck down the work piece right away if the valve and hoses are not too small.

[dmidkiff]

Thanks Ron, I thought time might be a factor but had not considered the HG. Should that spec be on the label?

G., thanks for that info. I may not use the vacuum for pods too much but wanted to have enough CFM if needed for pod/jig. The main use I am thinking about is bagging and stabilizing small blocks of wood.

John and Gerry, thanks for your input. I don't think I'll need the tank but know that it will work if I do.

I will have to call and ask these questions before I purchase. I should have paid more attention to Bill P when he talked about vacuum.

[bob_dodd]

I think Robinair vacuum pumps are generally used to pull vacuum on air conditioner systems during repair , if its this type , it has a tank with oil in it , after running a while there is a oil mist coming out of unit , just something to consider , as there are other options

[Ger21]

>> With the reservoir, it has to evacuate 6 gal of air.

Unless you pump the reservoir down first!

I was referring to after the initial suction, when he said it would drop to 15-20" Hg.
While the tank may help with initial pull, it's a hindrance once vacuum starts to leak. Provided your pump is pulling more air than is leaking, a pump without a tank will achieve higher vacuum faster than a pump with a tank.

[Ger21]

Dave, it depends a bit on what you'll be holding down. You can get away with 2-3 CFM with non porous materials, but you'd want more with more porous material like MDF. You really can't have too much CFM.

AS Bob said, make sure it's not an oil filled pump, as they can spew large amounts of oil.

[Roy Harding]

For vacuum bagging, I don't think the pump is much of a factor. Before I made a Venturi vacuum pump, I used a hand pump to evacuate vacuum bags when veneering. Worked like a charm. (You can see what I'm talking about here (http://www.roarockit.com/tap.php?id=13).)

Edited to add - the above applies to vacuum bagging ONLY, won't work for clamping for all the reasons discussed by others.

[dmidkiff]

Thanks Bob, Gerry and Roy, I will have to check because I don't want oil misting out in the shop. Even though I will mainly use for bagging, I'm sure there will be occasional hold down use. Thanks again guys.

[rhfurniture]

I have a Busch 1.1kw oil filled pump (out of a cake factory) for pucks and it works like a dream. It only starts to smell if the vacuum gets much below 20 in HG - ie the cfm goes up.
R

[Ger21]

I missed the part about vacuum bagging. For vacuum bagging, then you do want to use a reservoir (tank), to reduce the pump cycling on/off. Check out the designs at www.joewoodworker.com