Vacuum pump rebuild

Every fusor and fusion system seems to need a vacuum. This area is for detailed discussion of vacuum systems, materials, gauging, etc. related to fusor or fusion research.
Jerry Biehler
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Re: Vacuum pump rebuild

Post by Jerry Biehler » Wed Apr 11, 2018 5:48 am

Other than megging it and current the rest of the tests are not important. Put it together and get it working.

Bruce Meagher
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Re: Vacuum pump rebuild

Post by Bruce Meagher » Wed Apr 11, 2018 5:18 pm

Patience you must have, my old Padawan.

The motor is complete. In fact, Tyler just finished making some measurements with the Prony brake we assembled. Next, he has to cracked open the pump side and try to get it back into a usable state. Given the current pace he's still a few weeks/months away from his first vacuum test.

BTW, I respectfully disagree that the other tests are not important. For the young folks (and old folks too) I think the fusor journey is about getting some practical hands on experience in a number of diverse areas. Tests and measurements are key elements of that experience. I have a half dozen working pumps, but why pass up an opportunity to look under the hood to gain a little better understanding of how they work.

Bruce

Tyler Meagher
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Re: Vacuum pump rebuild

Post by Tyler Meagher » Thu Apr 12, 2018 2:57 am

My dad and I built a Prony brake to measure the horsepower of the motor. We used this article:

http://chestofbooks.com/crafts/popular- ... otors.html

The first picture is the Prony brake setup. The second picture is measuring the input power and the mechanical horsepower. The third picture is a graph of motor efficiency vs measured horsepower. The forth picture is the first look inside of the pump. It looks much worse than the motor.
Attachments
IMG_8.JPG
IMG_9.JPG
Motor efficiency.jpg
IMG_10.JPG

John Futter
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Re: Vacuum pump rebuild

Post by John Futter » Thu Apr 12, 2018 7:12 pm

I was surprised at how bad the motor efficiency was, but then I realised you are not measuring the phase agle of the current vs voltage.
So the actual power will be alot less due to current and voltage not being in phase.
analog devices make some brilliant metering chips ADE7751 that are simple to setup and although designed for kW/Hr meters some have an analog output (CF) of instantaneous power as well as the watthour pulse output

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Rich Feldman
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Re: Vacuum pump rebuild

Post by Rich Feldman » Thu Apr 12, 2018 11:37 pm

Good catch, John. The exercise is simpler with DC motors.

Compliments to the Meaghers on the Prony brake. Never seen one like that for real. Once I ad-libbed a motor efficiency demo, using an analog "true wattmeter" and a brake made of wood, shaped like:
brake2.JPG
The brake collar tightness on motor shaft was adjusted with a screw and wingnut. Soon the shaft got hot, the wood began to smoke, and I bet the friction changed. I guess we could figure the mechanical power from torque x rotation rate, or from matching the amount of smoke when the brake is clamped onto a soldering iron. :-)

It being break time, I whipped up an AC phase angle demo in Excel instead of finding one on the Internet. Simple arithmetic instead of trigonometry and calculus, for Tyler's benefit.

It shows instantaneous voltage, current, and power every 10 degrees for 2 whole cycles. Voltage and current are signed values, but when they are both negative their product P = V * I is still positive. It peaks at 240 watts in each half cycle, and averages out to 120 watts.
pf0.JPG

In this demo the sinusoid data points are computed from the control knob values entered in blue cells.
The values in Average and RMS boxes to the left are computed from the same numbers that are charted.

When current has same intensity, but lags voltage by 40 degrees, the average power is down to 92 watts. At some instants the power is negative.
pf40.JPG
Ooh, the forum let me post an Excel file. See what happens when the lagging current phase is set to 80 degrees (unloaded motor, perhaps), or negative angles (a capacitive load), or near 180 degrees (an alternator with resistive load, or a wattmeter with I or V connection made backwards).
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rms_demo.xlsx
(23.4 KiB) Downloaded 51 times
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Bruce Meagher
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Re: Vacuum pump rebuild

Post by Bruce Meagher » Fri Apr 13, 2018 2:01 am

Oops, my mistake! John, thanks for pointing out the error. I was trying to keep the exercise really simple, but that doesn’t work when you're doing it wrong! Rich, thanks for the spreadsheet and explanation. We'll spend some time talking about it, and re-run the experiment correctly when we have the proper measurement setup. In hindsight this is probably a little advance for a first look at electricity, but is a great example of why it's important to have other people review what you're doing.

Bruce

John Futter
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Re: Vacuum pump rebuild

Post by John Futter » Fri Apr 13, 2018 8:15 am

Bruce, Rich, & Tyler

Sorry to rain on the parade, but Tyler now has to learn something that most EE's only get very late in the course.
It reminds me of my youth when with little or should I say no knowledge I thought I could light a flouro tube using a magneto a battey for the tube filaments and direct connect to the 230 volt mains.
Never the less the resulting explosion and glass going everywhere except on me (read very lucky) put me off playing with mains until I learnt how they use inductive ballasts to limit tube current--- much later in life.

So now we have introduced power factor. Tyler I hope your maths is strong.

But first make the vac pump look as good as the motor!!

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Richard Hull
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Re: Vacuum pump rebuild

Post by Richard Hull » Fri Apr 13, 2018 1:57 pm

Ugh.....That photo of the guts of the pump is typical of a pump that pumped a lot of moist air for a long time (months/years) with no oil change and then stored for years. It represents what is usually a pump's death and an indication that a new pump is a good idea.

Fighting back from situations like this can be fun, instructive, expensive and often not worth the effort. All the very best in this resurrection effort.
Sometimes it looks far worse than it is....Other times, it is far worse than it looks.

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
Retired now...Doing only what I want and not what I should...every day is a saturday.

Jerry Biehler
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Re: Vacuum pump rebuild

Post by Jerry Biehler » Wed Apr 18, 2018 3:26 am

Yep, unbolt the pump and check the rotor and stator. If there is ANY pitting the pump is scrap. That probably should have been the first thing that was done.

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Richard Hull
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Re: Vacuum pump rebuild

Post by Richard Hull » Wed Apr 18, 2018 7:34 pm

I didn't want to say it, but Jerry is right on. #1 check out what really makes the vacuum. A nice, pretty, clean, smooth running motor married to it's special pump shell never makes a vacuum.

This is why I love belt drive pumps. Quiet running and separate unit pump and motor. The pump system doesn't have to have its special motor working at the same time as its pump. Any motor will work a belt drive pump..........and the motor will power any pump housing.

Any pump housing containing a pitted rotor, damaged blades or especially a pitted internal round housing is typically junk yard bound. How do you know this without opening the case?? If it is direct drive and the motor won't run, you will never know until you inspect it.

With a belt drive, if the motor runs and the pump turns you can vacuum test the system.

I would not hold out much hope for that rusty mass in your image.

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
Retired now...Doing only what I want and not what I should...every day is a saturday.

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