Trouble Getting Turbo Running

[Jeremy Adams]

Today I tried running my turbo to pump down my vacuum chamber, and it ran fine for the first minute until the controller showed a red light and turned off. The light indicated the problem was "rotor locked". What does this mean, and what can I do to fix it?

Some specifics on my vacuum setup- my pump is a turbotorr 3131. For those not familiar, it is an old turbo that was used in the 80s by NASA and last serviced in the 90's. It's like any turbo with a stack and induction motor at the bottom. I have not greased it or done anything to service it, and maybe that is the problem. When it first starts running it sounds fine, but at a higher frequency it gets a slight metal on metal sound. My controller is a 3133 turbotorr (I use the potentiometer to adjust the output to a lower frequency for the 3131 input).

[Jerry Biehler]

Wow, that's an antique.

I dont see a roughing pump. A turbo will not run without one for long, it will fault out after it is unable to reach speed.

If you do have a roughing pump it might not be good enough, this is probably a straight turbo and not a turbo-drag. Turbo drag pumps will operate at much higher fore pressures. If you are using a cheap or undersized roughing pump it may be exceeding foreline pressure.

[Jerry Biehler]

Also pull off the adapter and try spinning the rotor, you may have seized the bearings. The rotor should spin easily by hand.

I never recommend buying something as old as this guy. Too much to go wrong.

[Richard Hull]

"Slight metal on metal sound"....Not good.

Richard Hull

[Jerry Biehler]

ugh. Didn't see that in the post. You get to find a new turbo, probably.

[John Futter]

Jeremy
Please tell me that you are using a backing pump??
What is the backing pressure as you run the pump up??
If you run the pump with the backing port blanked off, the pump will pressurise the lower blades until they bend upwards and hit the stator blades

[Richard Hull]

John is correct. If you had a good pump and ran it up sealed off or without a roughing pump, you might not have a good pump now....

Vacuum stuff is critical in how it must be started and run. This is for secondary diff pumps and turbos, especially.

Richard Hull

[Jeremy Adams]

I appreciate the feedback.

I am not running it with a backing pump. The pumps pressure output in not closed off or anything, so no worries there. It spins easily when I turn it by hand like a good turbo should. The 'metal on metal sound' I mentioned might've just been mistaken for the noise of the stack spinning. It is pretty loud when it spins fast and I don't think any of the blades are touching or anything bad like that.

The pump output is definitely lower pressure as a function of time when it starts pumping down the chamber (from what I can feel when I put my hand by the output).

Maybe I do need a roughing pump to run it longer, but what troubles me is that the manual says it can run fine on it's own and pump to fairly low pressures without a roughing pump. Therefore I question whether not having the roughing pump is the direct cause for it stopping after a minute with the "rotor locked" sigh on the controller.

Maybe the problem is due to the controller, or maybe it's not greased up enough in it's bearings so the rotor is having trouble spinning at higher speeds? Would a feasible next step be to grease the vacuum and see if it runs longer? I am willing to purchase a roughing pump to get lower pressures but I'm skeptical that not having this is actually causing the turbo to literally stop running after 1 minute

[Andrew Seltzman]

A turbo will absolutely need a backing pump to operate properly, it can not pump against atmospheric pressure.

The seargent welch turbo pumps are fairly tolerant against damage, so it's probably still ok. At atmospheric pressure the air friction prevents the pump from spinning up to full speed and is causing the rotor locked indicator when the controller realizes it is not up to speed after a certain amount of time.

[Rich Feldman]

Uh-oh. We all know better than to debate questions which have factual answers.

Jeremy, would you mind posting a picture or scan (or word-for-word quote, or Internet link) of your manual, where it says it's OK to run with no backing pump? Does the manual have charts or tables of pumping performance with the outlet at atmospheric pressure, and at reduced pressure?


How does your turbo inlet pressure behave today, during the problematic start sequence?
It would at least be very interesting to hook up a backing pump. Even a diaphragm pump or refrigeration compressor or water aspirator. Many rooms where I work have vacuum on tap, for mechanical equipment, with 2 and 3 inch copper pipes back to the central pump.
How does your inlet pressure behave if you start the turbo pump motor after system is evacuated to the limit of the backing pump?

[Jerry Biehler]

The data sheet here specifically says you need a pump for roughing and backing, 12CFM for your pump:

http://www.rtftechnologies.org/Design/A ... -specs.PDF

Bearings need a specific amount of grease, many spec about 30% fill and less is used the faster they run. Too much grease and things get hot and go south very quickly.

[Jeremy Adams]

I'll use a roughing pump, you're right.

I have a two stage 5-CFM roughing pump already, but do you think this would make a difference? I could try it out but I'd rather not go through the difficulty of connecting it to our turbo output if a better one is needed to make It work. The manual suggests a roughing pump with 12 CFM. What brands are good to look into for roughing pumps?

[Andrew Seltzman]

The 2 stage 5-CFM should be fine as ling as it can pull own into the 10s of mTorr. You would only need he higher CFM if pumping higher gas loads that are not typically encountered in a fusor. The backing pump would be required. What model do you have ant what is it's rated ultimate pressure?

[Jerry Biehler]

You need to put a thermocouple or pirani gauge on the foreline and watch the pressure. I am not sure what the max foreline pressure will be but these old turbos are more sensitive to high fore pressure than modern turbo-drag pumps. It also does not hurt to have a vacuum reservoir on the foreline, it can help handle and smooth out any intermittent high gas loads with a smaller roughing pump.