FAQ - Bolt that turbo down!!

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Richard Hull
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FAQ - Bolt that turbo down!!

Post by Richard Hull »

It seems that the diff pump is being replaced in the amateur vacuum system by the Turbo pump. A few tips are important for the owner/operator of a turbo pump.

1. If purchased used, assuming it is complete and working, you should oil the pumps bearings. The oil can be expensive, but so was the turbo. You will typically need only a few drops, but have to purchase enough for 40 turbo pumps maintenance for 20 years. Refer to the owner/operator manual on how to oil your pump's bearings.

2. Make sure you have a fine mesh screen that is made to fit over the large open throat of you pump's inlet. Without this much needed screen any particle of hard material accidentally falling into the pump can hit the blades turning at 90,000 rpm and tear the entire blade assembly up, ruining the pump forever. All new pumps tend to have this accessory provided. Make sure your pump has one!

3. Never operate a turbo pump at full speed by just sitting it on a table!!! All turbo pumps must be firmly bolted to a table or specially designed vacuum system cage or cart.

Why??

A turbo is like a gyroscope that can't have its rotating mass, (blade system), disturbed. At that speed, the blade system has what is termed "rigidity in space". This is great in a gyro as its high speed rotating mass can tumble over 3 axes in its pivoting ring system as its case is moved all over the place. For the tight fitting blade group in the turbo, it can be a bomb ready to explode destroying the blade system should the turbo body suffer a sharp mechanical sideways shock or rapid acceleration motion while running.

You are now warned. save your expensive turbo! Mount it firmly. Even if mounted firmly to a table or cage, never move the table or cage while the turbo is spinning.

Most turbos have threaded holes for mounting at the base. Make use of them.

Many turbos are sensitive to their mounting orientation. Be sure to check the manufacturer's suggested mounting orientation before you bolt the turbo down.

4. A few turbo pumps have a water inlet and outlet for cooling near their base. You will most likely not need to use this as your pump will run for very short periods separated by long periods of non-use. This is provided for industries where 24-7 operation is the norm.

5. As long as the pump is firmly bolted to a non-vibrating, firm platform, valves and plumbing may be attached and operated normally. However, be sure to use the best fittings and connections to the turbo as it is your final chance to pump a deep vacuum.

Beyond the above, the turbo pump is an item that will not need any real maintenance common to the diffusion pump. Enjoy its convenience and superb performance.

Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
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Dennis P Brown
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Re: FAQ - Bolt that turbo down!!

Post by Dennis P Brown »

The bane of any turbo is when something does get in and damages the blades or if the blades are bent because of accidental air entry while running. However, just because of these types of damage and the turbo no longer runs, don't give up on the turbo - bent blades can be easily repaired. Even a limited number of broken blades can be delt with depending on location. Of course, if new, opening the case will void a warranty but broken/bent blades are not covered. If you suspect a bearing (not debris) and still under warranty, then best to talk to them to determine if it is covered.

I have repaired a number of turbos that have had blade damage - one had a bolt jammed in the blades! The issue one must address is if they are comfortable with disassembly of a turbo - that is, remove a series of (usually) Allen bolts and gently sliding the turbo outer case off the blades. If yes, then certainly this is worth doing when 1) blades are just bent or 2) an item is jammed in the turbo 3) one or two blades are broken.

First step is to invert the turbo and gently shake out any debris, so it falls out. Next, see if you can turn the rotor by hand - never use excessive pressure. Using one finger at the rotor hub, see if the unit turns/spins. It should turn freely and without any scraping sound if all is well. However, if jammed, then go to the next step because either blades are touching, or a bearing is the issue. If it does rotate but you hear any noise like scraping, then the blades are bent but the bearing should be ok. Finally, if it turns freely with no noise, then likely all is fine with the blades, and one should test the motor/bearings.

So, to see if all is ok (only if you hear no sound when manually spun), then run a test in air. To run a test momentarily apply power to the unit with it on a flat surface and being certain to hold the unit in place. Apply power for just a tiny fraction of a second - never run to high speed. If nothing happens with power applied (but you can spin the rotor) then likely an electrical issue. If it starts to spin rapidly (again, power only a fraction of a second) with zero sounds like scraping then no blades are bent. Then it might be an issue relative to the bearings - that is failing under load. That is not generally a blade issue, and you should decide if you can replace a bearing.

Unlike replacing bearings (which I have not done), removing the case for most turbo's is rather easy. Locate the Allen bolt locations that hold the case together. These are generally located at the base of the unit. With the proper sized an Allen wrench loosen all the bolts using a partial turn. This should follow the standard vacuum bolt removal pattern. That is, loosen a bolt using a particle turn, then jump to the opposite side bolt and do the same. Then do a bolt 90 degrees from that one, then jump to its opposite side bolt and so on till all bolts have been partly loosen (but still somewhat tight.) Continue partial turns following this pattern till all can be removed. The bolts might have 'Loc tight' on the heads but this is just to determine warranty violations. So just break those bolts since one is repairing it themselves.

Slowly and gently slide the turbo body free of the blades/motor assembly. When sliding the case from the turbo, keep the base flat on the table and lift vertically. Do not let the turbo go to its side. There are sets of 'loose blades' (called stationary blades) inside and their orientation and order must be preserved. If the case is stuck, do not force it. Likely that there is still debris so kept it together and rotate it upside down and try to dislodge the debris. If nothing comes out, decide if forcible removal is acceptable to you. That is, if the turbo will be junk anyway. It's possible a few bent blades are touching the case and with extra force will allow the unit to slide apart. This could break blades but if the unit is junk anyway, worth a try.

Once the unit is apart, you will see what happen - if an object is inside or blades are bent or the unit is shredded (and unrecoverable in that case.) If there is a large object, first determine if it can be easily removed without further disassembly but more then likely this will not be possible due to stationary blades being in the way. Then these stationary' blades will need to be removed.

Looking at the unit from the side you will see that there are removable "stationary" disks that have 'vent-like' like raised sections on the removable 'disk' sections. These stationary disks also split into half sections for easy removal. Removal of these stationary disks is straightforward. They have two 'keyed' sections that hold/lock the two units together. To remove one of these stationary disks, simply raise the edge of one of these disks slightly to separate it from its 'interlocking' section of its partner. Then gently pull it out.

Starting at the top or bottom of the turbo 'stack' (your choice but remember where you started) remove the two section disks and set them down in the same orientation they were in the stack. Work your way up or down through all these stationary disks sets setting each together as a unit next to the previous ones - order matters when reassembling. That is, for some turbos (bigger units) the thickness and shape of these stationary blades change with location in the stack. So keeping these units in order is essential. Also, the top side of these units (orientation) must be maintained - that is, the top side on these disks must be put back the same way in the stack.

This whole thing is very obvious when you see the turbo's blade system. Just keep these pointers in mind and the disassembly is very straightforward.

Again, note which parts of the turbo rotor has removable stationary blade sections. These alternate between blades that are attached to the rotor hub.

After removing all these 'stationary' disks, from between the fixed blades (the ones attached to the rotor hub) you can see these rotor blades clearly. If there is any object still in the blades, it should have been exposed during this process and using tweezers, removed.

Gentilly try and see if you can spin these blades again. If they don't spin at all, then most likely the bearing is seized. If they turn but stop quickly, and there are no blades touching such that they are causing the sound, then again, the bearing is likely failing. At this point (the unit that still turns but poorly) it might be worth trying to oil the bearing. Then turn it a few times to work in the oil and see if the oil allows it to then turn freely (unlikely but worth a try.) If the bearing is a sealed unit, well replacement is the best route. That will often mean using a bearing puller and that, I think, others here have described.

Now with all the stationary blades removed, and the unit turns freely, carefully look that the rotor blades in a horizontal direction. They should all be parallel and make no contact with any other blade. It should be obvious if any are bent.

Spin the unit again (by hand only - never apply power to the turbo for these steps!) Watch these blades rotate and see if they all spin in a perfectly horizontal manner - no up or down motion seen.

If some are bent 'out-of-plane', gently bend them back into proper horizontal position using a needle nose plier (but be careful.) Grasp the blade close to were it is attached to the hub to apply force. They bend very easily. Use only enough force to get it to bend back to its proper position. Spin the unit again and see if this fixed the issue.

Likewise, if one or more are bent in a manner that they do not match the 'angle' that the other blades suspend, then they need to be slightly 'twisted' to get back to their proper angle. This can be tricky since this requires bending the blade's angle. To do this, grasp the tip to mid-section of the blade. Be very gentile applying a torque force - this process can easily break off the blade so make small changes. Try not to do this to many times since that will fatigue the metal leading to failure.

If you see that a blade is missing and or if one breaks off during this correction process, don't worry. The turbo is till usable. Just locate the exact opposite blade on the rotor (in the same plane!) and break that one off. This will maintain the balance and allow the turbo to still operate. I've done this for two turbo's and they have run fine. I've never had more than three blades broken (it was the one with the bolt lodged in it. All were on different rotor sections) but breaking off its opposite has worked for me.

Back to the unit that turns freely with no broken blades: look at all the half section blades that you removed. And note if any are warped or individual blades appear warped (not perfectly flat - not talking about the vent holes.) If the unit is warped, gently bend it flat again. Use very little force - these are delicate units. Do not close off the vent holes.

This is a good time to see how these stationary blades fit and lock together. Practice doing this with all the removed units. They should lock together and lie perfectly flat. If not properly interlocked, one side will stick slightly up. Just reassemble as needed until you get a feel for this process. It is important to do this properly before reassembling the system.

Now that you know how they lock together, reassemble the first set of stationary blades back into the turbo rotor section. Be certain to center the stationary blades and that they interlock properly. This is important - if misaligned, you will likely hear scraping and think it is due to bent blades - which in this case, isn't the case. Rather, just mis-aligned sections.

When properly seated/interlocked, try rotating the turbo again by hand. Carefully watch the hub blades turn and listen for any scraping. If so, note where the blades are striking and if it is a rotor blade or one of the half section blades or it could be both. Remove the stationary section and bent the offending part as needed. Whether this be a rotor blade or stationary unit. This is an iteration process.

When the unit turns with no noise, move on to adding the next stationary section and retest. If noise, locate the offending area and bend as needed.

Continue until all the stationary sections are back into place. The unit should turn freely now without any noise. The turbo is then ready to place the case back on.

Carefully make sure all the stationary blade sets are properly together and not sticking out, misaligned or not properly locked together. Then slide the case on and slightly tighten three or four bolts. Carefully using your finger again at the hub of the rotor, spin the rotor blades. No sound should be heard. If you hear scraping, disassemble and redo this process (I've done this three times before the rotor spun freely.)

When no sound is heard, tighten all the Allen bolts using the proper tighten methodology mentioned previously. Again, spin the unit and confirm it is still free with no scraping sound. If not, start over (again, happen to me once - one blade was still an issue. Sometimes its that one of the stationary blade sets didn't seat proper and was misaligned.)

This technique sounds tedious but is far easier then this description makes it sound. I can do a badly bent blade system in under an hour even with a few re-disassembles. Just take it slow, keep all the 'stationary' blade sets in proper order during disassemble/reassembly, and never use too much force and all should go smoothly.

In this way, a damaged turbo can be gotten back into service and work fine again.
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