Do all vacuum pumps smoke?

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raar25

Member
Joined
Mar 29, 2011
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770
Location
Glastonbury CT
I bought a HF pump for the stabilizing chamber I finally got around to making but the steam coming out fills the shop with a cloud of fine mist. Is this just air and moisture coming from the chamber or oil mist from the pump oil? The pump pulls down to 28 hg and does a nice job otherwise but I was just wondering if I should return it for another unit (also HF) or if this is just a natural by product of the process? :confused:

Thanks,
Ray
 
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My pump does not smoke or send out any visible vapors. Check the pump oil level to see if you are losing oil. Is the pump reservoir overfilled? Is the stabilizing fluid bubbling high enough to be sucked into the pump? If you run the pump w/o fluid in the chamber do you get any smoke?
 
Don't return the pump. All oil filled pumps will put out a mist while there is air moving through the pump. As soon as the chamber gets pulled down to full vacuum, the oil mist usually stops. If you are seeing an oil mist after 30 minutes or so, this usually means you have a leak in your system.

I took the liberty of looking up the elevation for Glastonbury CT and see that it is 417' above sea level. Your maximum theoretical vacuum is 29.47 inHg and that pump will do much better than 28" at your elevation. This indicates a significant vacuum leak and is most likely the cause of the oil mist. Check all of your connections as well as where the lid meets the chamber to see if you can find a leak. To check the chamber, put some water in it and pull as much vac as you can. Then tilt the chamber so the junction between the chamber and lid is submerged some. Assuming you have at least a clear lid, you will be able to see any bubbles if there is a leak. Any bubbles at all indicate leakage. To check the fittings, spray them with shaving cream. If there is a leak the shaving cream will disappear at the leak.

If none of this is clear enough and you need more help, please don't hesitate to give me a call. My number is 512-738-0775. I have done this just a little bit so I am sure I can help!
 
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Thank you Curtis that is very generous. I will call you once I do some diagnostics. depending on whether I find a leak or am dealing with an an inaccurate guage and once I have completed some stabilizing I will pick your brain on specific questions so I dont waste too much of your time. Since I paid a whole $6 for the vacuum guage which did not come with a calibration cert, I would not be surprised if it was off by 5%

Regards,
Ray
 
Your gauge is most likely fine. A $6 gauge is going to be a 3-2-3 gauge. This means it is +/- 3% for the first and last 3rd of the gauge scale and +/- 2% in the middle third. The excessive misting strongly points to a leak though.
 
Of course you were right Curtis. I found a fitting with a leak and fixed that now I am getting just north of 29 hg and the bubbling is much more dramatic and the pump sounds like it is working a little harder as well. The mist did stop after a little while as you thought it would and just to double check I shut the pump off and let it sit for a while without cracking the valve and the chamber held the vacuum for a couple hours until I opened the valve a couple hours later.

Thanks for your help. I am going to get some experience with the chamber and then will probably give you a call with specific questions.

Thanks again for steering me in the right direction.
 
I too have a HF pump. What I do is drape a rag over the exhaust port. Most of the vapors are caught in the rag and I don't have the mist floating around the shop. Just the way I do it. Dennis
 
Ray,

One thing to note...NEVER shut your pump off while it is under vacuum. Two things can happen. One, when you shut down with the pump under load, you trap some oil in the cycle. Then, the next time you start the pump it puts extra strain on a coupler that joins the motor to the pump itself. This coupler is designed to sheer under extra load to keep from damaging your motor. Repeated stress of starting the pump under load will cause that coupler to fail prematurely. It will also cause the pump to spit oil out the exhaust on the next startup many times.

The other thing it can do is the vacuum in the chamber can actually suck the oil out of your pump. Some pumps have check valves to prevent this but many do not. If this happens, it will suck the oil out of the pump and dump into your chamber ruining any resin you have in there. Seen that many times with customers!

It is always best practice to turn on the pump with all valves open and slowly close them, controlling the foaming. Then, leave the pump running the entire time you are stabilizing so that you are moving the maximum amount of air. Then, when you are done, open the valve and allow the pump to settle down. It will change noise. When the sound smooths out, shut off the pump. This will keep your pump running in good shape for years to come.
 
Great information for sure. Here is a little more. It is actually the oil in the pump that seals the impeller on the pump and causes the vacuum to happen. The vacuum pump oil is hydroscopic so it absorbes the moisture in the air passing through it. (In the a/c business we use the pump to help remove moisture and air from the system before charging it with refrigerant.). When the oil becomes saturated with moisture it will no longer pull a vacuum or the pump will work way harder than it should to pull a vacuum. So the oils must be changed when it becomes saturated. Always keep the pump sealed to use the oil longer. (In the a/c business there is way more to the vacuum process then what I am saying here). Also most all standard hoses bought to charge an a/c unit with refrigerant are not designed for negitive pressure, only positive pressure, so the fitting will need to be tightened way tighter than normal to get the rubber fitting to seal. I know the hose may say differently but you can trust me on this. Also the diameter of the fittings and the hoses will determin how quickly the vacuum can be pulled. The hose for a screw on fitting needs a double gasket arrangement. Not just two gaskets in the same fitting. Probably more info than what you need, just what to help. I hope some day to use all this good equipment that Curtis sells to make some pen blanks. Until then I will continue to buy the wonderful blanks I find on the IAP. Good vacuuming to all.
 
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