Testing seal drag

[wdyasq]

        part         grams      Oz    radius    radius cm    oz/in    g/cm

Timkin    471750    123.00    4.34    1.24    3.14    3.51    39.21

       w/o spring      94.00    3.32    1.24    3.14    2.68    29.97

Timkin    32x50x82 186.00    6.56    1.24    3.14    5.31    59.29

    w/o spring        155.00    5.47    1.24    3.14    4.43    49.41

Dexter    stock       124.00    4.37    1.24    3.14    3.54    39.53

Testing rig

Procedure - spindle shaft where seal was to ride was polished. Bearing was nylon on steel and oiled.  Seal was installed in holder, seal contact area was lubed with 5-30W oil between each test.  Water was added to bucket until it started to move, bucket and water was weighed. For each condition this was repeated at least three times.  The weights were recorded.  There was little deviation in the weights.

Conclusion - "It ain't worth it." If oil can be used as a lubricant, the seal drag is in ounce inches.  The spring adds some.  After 'running the numbers' it is apparent the standard seal which does not have a spring is about as good as it gets. Foot pounds are .021 to .042.  A horsepower is 550 foot pounds a second. At 600 RPM the seal drag is still less than .01% of a horsepower.

Research is a good thing. Until I actually ran the numbers "seal drag" was an unknown in my knowledge.

Ron

[BT Humble]

I read the title of your post, and the first thing that popped into my mind was "Wonder if he's had any angry calls from the RSPCA/ASPCA yet?" ;-)

BTH

[wdyasq]

No seals this far inland - have to use neighbor's cats.

Ron

[willib]

i did some testing of the seal drag on the hub that i'm gonna use





to break it free from a dead stop took 2.5 Newtons at a radius of 2.5 inches ..

not much really

[Chagrin]

You're testing static friction, though. You should have given the bucket a push to see if it would continue moving -- that force would be more indicative of the drag that the seal causes.

[kitno455]

was there a test with no seal?

allan

[wdyasq]

Yes, there was such a test. It would spinup with an empty bucket and would spin with just the bail. Would not move with line and "hook" only. By using the Nylon and Delrin as a bearing and seal holder I was able to get inertia very low.

I did give the holder a slight spin with a finger as I added the water.  One or two grams of water difference and just the rocking of the bucket would cause the seal holder to turn. I was amazed at the repeatability of the weight needed to rotate the seal holder.  I had to borrow the braided line off my plumb-bob as I could not find my spool of regular braided line.

I plan on using this for a cap:

http://www.etrailerpart.com/prolube.htm

I will use thin synthetic oil as a lube. I will also make sure the oil is lower than the seal but deep enough to keep the bearings lubed.  I have seen a "water thin" oil they use in racing engines and know where I can get enough at the proper cost for a few hubs.  

Ron

[terry5732]

I could never understand someone putting bearings out in the elements unsealed even if it dropped your power by 50%. And I always suspected it was a very low loss. For sure these number go even lower as the seals "burn in".

[RP]

Ron,

I didn't think of this earlier but while you've sucessfully measured static or 'breakaway' friction, it's a small step to get dynamic friction.  If you have the time, inclination and stuff:

You could connect your test assembly to a small motor (via belt or direct drive) and measure the motor current required to hold it at speed for different seals.  

As an idea to make it a senstive test, maybe a small PM motor from a toy driving the assembly via a wide rubberband belt.  This kind of motor would be well into the linear part of its current/torque curve just spinning the thing against bearing friction.  Any changes due to seal friction should be easily identifiable by motor current.

The torque/current ratio can be calibrated by tying two pill bottles together using a few feet of thread.  Hang the pair over your test assembly and add a weight to one bottle.  Comparing the unbalanced weight load to the change in current gives you your curve.

With this info and an estimate of rpm it's only a small step to know how many watts are lost to seal friction in mill.

It's all so clear in my mind since I don't have to do the work!  :-)

[wdyasq]

"You could connect your test assembly to a small motor (via belt or direct drive) and measure the motor current required to hold it at speed for different seals."

Then I could test something else? - This was not planned as a school science project.

No, I've satisfied myself the seal is not a large drag factor. I will proceed to work on a style blade mount where I can easily switch blades and carve proper airfoils. I do believe many are leaving form 15-35% of available power by not using a modern, fat, low drag factor airfoil with a big root section.

But, any testing will be just a guess as there will not be the type wind speed measuring devices to accurately gauge airspeed.  Fortunately, I do have tools that will be able to measure RPM and output of the mill.  Even with this it will only be a guess as to which blades will actually work better.  As I have stated before a 10% change on wind speed is a 37.2% change in power.  This is a bit more than I would think a good blade-set would give. Even if I one got a correct certified anemometer, would they properly correct for altitude density and temperature?  What about humidity?

No, I think my next test will be for coil voltage at  particular RPMs.  Then I can verify the coil configuration and SWAG a set of blades. SWAG is a scientific term meaning Sophisticated Wild _rse Guess, FYI.

Ron

[willib]

You cant quit now!

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