vacuum problem

[curtis rosche]

ok, so i got my vacuum pump hooked up, and i am working on the chuck part, but before i made that i figured i should test it out. its a 4 cfm pump, and it should be pulling between 20 and 30 inches. when i turned it on and held my finger on the end of the spindle the guage only went to 10 inches. what do i do now?

[Steve Schlumpf]

Look for a vacuum leak!

[curtis rosche]

how do you do that. its not like it can blow bubbles

[David Christopher]

keep your finger over the end and spray WD 40 on the pieces and watch your gauge .....or unhook from vacuum pump and apply a small amount of air presure and spray soap and look for bubbles

[Kyle Iwamoto]

Leave your finger on the tube, and turn the pump off. If the vacuum immediately falls to 0, you got a pretty good air leak. If it drops off slowly, or not at all, then your pump is having problems.
4 cfmin NOT a lot of flow. How long are you letting the pump run? Not knowing anything about your pump, most times the first 10" or so is pretty fast, then the pump has to work a little harder to draw over 20.

Once you determine you do have a leak, finding it is difficult. First questions I would have is did you use teflon tape/pipe sealant on everything? If your pump can handle a little water, spray some soap bubble solution, yes, the ones your kids play with, on the joints. A vacuum leak will pull in the little bubbles that form on the piping. Use a spray bottle that sprays a fine mist, like a Windex sprayer. The 409 sprayers spray the soap too fast and heavy.

No, I don't have a vacuum pump, but I do work with leak testing from time to time.

[curtis rosche]

should i have put that white tape stuff on the threads first?

[curtis rosche]

it falls straight to zero... but when i turn it back on it goes right to 10.

[Ryan Baker]

should i have put that white tape stuff on the threads first?

Teflon tape. Yes. You need a thread sealer or you will have big leaks at every fitting.

[Steve Schlumpf]

Curtis - not knowing how you have your pump set up - it is a little difficult to troubleshoot. First thing you have to do is use teflon tape at every junction to seal air leaks around the threads. Might be easier to start at the beginning and remove everything on the input side of your pump. Then attach the first section - properly taped - and check and see how high the vacuum goes when you plug the end with your finger. If it works - and it should - then add another section and test again. You should be able to build your system back - one section at a time - and know that all the leaks have been taken care of.

[Kyle Iwamoto]

If the vacuum drops fast and comes up fast, yes, you got a pretty good leak. Go to you local hardware store, and buy that white tape stuff. (teflon tape) Take apart all of your fittings and reassemble.

To properly use the tape, wrap in the direction of tightening. You only need to put 2 to 3 wraps on. Wrap tight enough to strech the tape as your'e going around the piping. Mistake #1 with teflon tape is using too much. Mistake #2 is not wrapping tightly or in the wrong direction. Wrapping in the wrong direction causes the tape to loosen and that creates air leaks.

You can also use pipe sealing compound, which is easy to use, however, that usually glues your piping together.

[Bernie Weishapl]

Curtis mix you up some soap and water. Either spray it on all your connections or paint it on. If you got a big leak you will see it.

[Don Eddard]

Curtis mix you up some soap and water. Either spray it on all your connections or paint it on. If you got a big leak you will see it.
Not necessarily on a vacuum system. If he can pressurize it like was suggested above, then the soapy water would help. I agree with Steve that it'd be easier to take it all apart and start over with the right plumbing techniques.

[curtis rosche]

i think one of the leaks is at the "sealed" bearing.

should the hose barbs get any nylon tape?

[Steve Schlumpf]

Curtis - you want the hose barbs to cut into the hose a little bit - that is what makes the air tight connection. If you suspect that it is loose and causing a leak - wrap a couple layers of the teflon tape over the hose/fitting junction and that should take care of any leaks.

[Cyril Griesbach]

Curtis, don't assume it's limited to leaks or the pump. I thought that with my mew system but found no leaks. My gauge would only show that I was getting 19hg and mostly less. Yesterday I set it up to finish some bowl bottoms and it only showed 8-9hg with a bowl on the chuck and it was on TIGHT. I think I need a new gauge so.....the question now is...what's the Surplus Center part numbers of the gauges you others are using?

[phil harold]

dont expect to get over 24 inHG with a rotary vane

also make sure your needle is on the guage is not binding and stopping at the 10 mark

I have seen cheap gauges give bad readings because they were banged and the scale metal scale deformed and the needle would only go to a certain point then stop

you can put a tube to your ear and use it like a stethoscope and listen to each connection to find a leak

then you could apply rtv silcone at the joint and turn the vacume on for a bit couple seconds then shut down the system and let it harden before use

but first make sure all your connections are made properly first
teflon tape and hose clamps before you use the silcone method to plug leaks
it is a last resort method...

[Eric Magruder]

What pump do you have, and is it new or used? If it's used you could have dirty veins in the pump. This can be corrected by running some carburetor cleaner through the pump - ONLY preform this cleaning in a very well ventilated area, outside is best.

As the others have suggested, you must use the Teflon tape on all pipe fitting connections, and any hose connections must be very tight - use hose clamps if necessary.

While you have everything apart test the pump with only the gauge connected to the vacuum port of the pump and see what reading you get. If you get a good reading assemble the rest of the system with the tape, testing as you go.

If you still have trouble post some photos of your setup if you can so we can see what your working with.

Good luck.

[curtis rosche]

i taped all the joints and now it works better. there are no leaks till it gets to the spindle. i kinked the hose right beforw the spindle and the gauge went up to 20hg so my spindle seems to be losing 10 hg.

the "sealed" bearing is leaking.

also, will a rubber toilet gasket work for the seal between the bowl and the pipe used as a chuck?