Replies

1. 
   dgreen | Jul 08, 2006 05:04am | #1

   It's a 3 cfm pump. Should work great, it should pull down to 29". Mines only half the cfm and it works very well, I have it mounted on a 30 gal tank.

   Since the house is on fire let us warm ourselves. ~Italian Proverb
2. 
   mudman | Jul 08, 2006 05:54am | #2

   I have seen (on this forum I think) discussions about this. Most recomended a pressure switch / regulator. There are some good sites out there devoted to Vac Bag work. Please keep us posted as I will likely go the same route as you.

   Pardon my spelling,

   Mike

   Make sure that your next project is beyond your skill and requires tools you don't have. You won't regret it.

3. 
   KeithNewton | Jul 09, 2006 06:13am | #3

   It should be fine. Here is a link just for vacuum bagging. http://www.vacupress.com/forum.htm

   The easiest way is to just run a hose straight to the bag, and just let it run. All of my pumps are piston type, but I have heard some people complain about those rotary pumps being loud, and putting a cloud of oil mist in the shop.

   If you choose to hook a tank into the line, you should have a T in the line and a valve to stop the flow to the bag so you can pre-draw a vacuum in the tank, then open it to quickly evacuate the air from the bag, then close the one to the tank unless you are using a vacuum pressure switch to cycle the pump on and off, and then you will need a check valve to prevent that type of pump from running backwards when the motor cycles off.

   good luck, this is a great skill to be adding to your bag of tricks.

1. 
   dgreen | Jul 09, 2006 06:33am | #4

   I use a T on the pump side of the tank so I can isolate the tank from the pump so that the pump does not have to start under vacuum and so that when shutting down the pump it is not in vacuum. This takes two valves obviously. On the work side of the tank is another valve for drawing a vacuum in the tank before evacuating the bag or holding fixture. My 2 stage rotary oil pump is very very quiet and even with 29" of vacuum in the tank does not even think about turning backwards with no power applied. I could imagine that happening with a carbon vane pump but not with a 2 stage oil. The pumps for HVAC are made to run for long periods not only to draw a vacuum but to boil off any moisture in the system. I have never seen any oil, vapor or otherwise escape my pump. It is important to change the oil on a regular basis as it breaks down and efficiency suffers.
   Since the house is on fire let us warm ourselves. ~Italian Proverb

1. 
   KeithNewton | Jul 09, 2006 07:15am | #5

   D, sorry,,,,,, I didn't look carefully enough at the spec.'s. Glad to hear that they are quiet and don't have the oil problem. I have a friend who got one a long time ago that looked a lot like those, but it suffered all of the aforementioned problems. I also have a larger Gast rotary vane one that does as well. I haven't used that one in over 10 years mainly because it is so loud. I have tried everything I could think of to muffle it, even thought about putting it outside, but I am afraid of what the neighbors would do.

1. 
   dgreen | Jul 09, 2006 07:23am | #6

   How big a Gast do you have? I gave up on the vane pumps not because of the noise but because the ones I could afford did'nt pull a deep enough vacuum for me. Gast is a well thought of pump maker. The ones I have heard were fairly quiet but they were small, 1/8 to 1/4 horse. I know they make some big ones.
   Since the house is on fire let us warm ourselves. ~Italian Proverb

1. 
   KeithNewton | Jul 09, 2006 07:55am | #7

   I think it is 3/4 hp. and the plumbing is all 1". It will really move a lot of air, but I don't think it would pull but about 20" hg. and is about as loud as a medium size chain-saw.Since I touched on the subject of pipe or tube size, since we are talking vacuum, the maximum pressure will be under -15#, so if you have a full vacuum at the pump end of the hose, the volume amount of air flowing in is proportional to the hose size, and the area quadruples when you double the diameter. For instance, the area for 1/4" is .0491 and 1/2" is .1963. Humm,,, I get 3/8" at .1104 which is more than double the area of 1/4". well do you get what I am driving at?

2. 
   dgreen | Jul 09, 2006 08:04am | #8

   I get the concept of area as related to cfm but I'm missing your point, I'm tired long day probably being a little dense. Afraid your going to have to spell it out.

    
   Since the house is on fire let us warm ourselves. ~Italian Proverb

2. 
   kevink | Jul 09, 2006 03:41pm | #9

   thanks dgreen and Keith for your helpful responses. Two more questions:1. What size hose shoud I buy?
   2. Should I buy a tank? Can a good tank be improvised or easily built?

1. 
   dgreen | Jul 09, 2006 04:09pm | #10

   Bigger is always better on the hose as far as flow is concerned but realisticly 1/2" is about the max for adequate flexibility and a lot of people use 3/8.

   Having a tank lets you pull a vacuum in the bag faster which is a good thing. The tank can be made from anything that will hold air, I use a surplus 30 gal compressor tank, the motor mounting flange on top gave me a good place to mount the pump.

   I've seen a couple of setups that used a 10 gallon portable air tank like you see at the box and automotive stores.
   Since the house is on fire let us warm ourselves. ~Italian Proverb

2. 
   KeithNewton | Jul 09, 2006 05:03pm | #11

   I would go with 3/8" without the tank to start with, and just let it run to start with. If you don't do large project that start with a large volume of air in the bag to start with, then you don't need the tank. I have had them on earlier set-ups, but don't anymore, my pump is fast enough, that I don't need it.Once your pump has been running for a while, if you can feel of it with your hands without feeling much heat, it should be fine to just let it run.

1. 
   kevink | Jul 10, 2006 12:22am | #12

   The project at hand is a large glue-up. I've got to veneer several flat panels that are roughly 2'x 11'. The veneer is rift white oak (birch or something for the backing), the substrate 3/4 mdf. If I use a slower setting adhesive ( i was thinking of a unibond mix ) instead of yellow glue do you think i'll be okay without the tank?thanks to you and d for your responses - they've been awesome

2. 
   KeithNewton | Jul 10, 2006 01:23am | #13

   Sure. do you already have a 12' bag? the hard part on things of that size is getting them into the bag. You will surely need another set of hands, and it would be a good idea to do a practice dry-run first so that things move along without any screw-ups.It is hard to shove something that long into a bag without it hanging on the bag, but what I do is to lay some 1/4" MDF or something to slide it on, or set the end onto something like a 1" to 2" roller that you can keep it balance on to keep the front end up so it won't hang on the bottom. also for things that long, I like to run something like hay baling-string or sky rope around the perimeter as I feed it in, so that the air from the far end has an easy path to travel to get over to the hose-end. Where the hose comes in, I like to have something cloth like a long shirtsleeve taped around the end of the hose. Then make sure that both ends of the string make contact with that. Go with the Unibond, you won't have enough time with the yellow, and it is not rigid enough.

3. 
   kevink | Jul 10, 2006 02:41am | #14

   I don't have a bag yet. I was thinking about getting one from either Vacu Press or Vacuum Laminating Technologies. Before I found the Fast Vac I thought that I would buying a pump from one of these guys too. Do you have any thoughts on these sources for a bag? What are your thoughts on building one a la joe woodworker?thanks