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Anyone do pull tests?
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By Scott O
From California
Apr 3, 2013
Batman Pinnacle

I'm retiring a pretty significant amount of soft goods - cord, draws (dynex), and slings because it's all 5-8 years old, and I'm fairly paranoid about soft goods. A few of them are unused or lightly used, but older than I'm willing to trust my life to. If anyone is willing to pull test them and share the results on MP, I'll gladly send them to you. I'll provide you with as much history on each item as I can to increase the value of the test.

I want to make sure they go to someone who really will share the results and do so in an informative, useful manner, so if you have a history of doing this, please link the post if you don't mind.

I'll pay shipping - you just have to wreck it and share the results.


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By Eric G.
Apr 4, 2013

Bump. I`d send some 5-year-old 8mm dyneema slings too.


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By Aric Datesman
Apr 4, 2013

Only person I know of anymore is Banquo over on ST, but it's once in a blue moon and I don't recall seeing him do soft goods.


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By mattm
From TX
Apr 4, 2013
Grande Grotto

I have a 10,000lb load cell setup I bought a while back. Problem is it needs to be calibrated with known loads over it's range. Not easy for me to do... That and I still need to trouble shoot my Porta Power. Won't pull back the "pull back" ram. First time "ebay deal" has burned me actually.

Any Advice Aric? Load cell is just gathering dust right now...


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By robrobrobrob
Apr 4, 2013

This is interesting to me. My wife has been considering writing up a grant for some pull/drop testing gear for her High School STEM/Engineering classes. Her idea would be to collect a bunch of information about the soft goods use through a web interface (age, use qualifications, storage), have the goods shipped, and then have the students work through testing it. Her thought is to create a LARGE database of test data of used gear.

However, she's not gotten the grant or the equipment yet. It sounds like it would be a useful thing to do. What does MP think? Any suggestions?


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By 20 kN
From Hawaii
Apr 4, 2013

I can pull-test just about anything except for cams. I have a ram with 27" of stroke. I could test them but I am going to be very busy for quite a long time. Anyway, having pull tested hundreds upon hundreds of feet of soft goods I can tell you that unless the item is damaged, extremely worn or chemically altered, it will probably fail around its rated strength.

Mattm, you have three options that I can think of:

1. Hang a calibrated or known weight off the cell.
2. Put an already calibrated cell inline with the test cell and lift a weight of an unknown value.
3. Use the mV/V value located on the load cell certificate.

The third option is by far the most accurate option and it is pretty much the standard for programing conditioners/ indicators.


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By Jon H
From Boulder
Apr 4, 2013
At the matching crux

Geir Hundal(sp?) who posts here under "Geir" has done a bunch of pull testing for mailed-in gear in the past. He might be interested.


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By Gunkiemike
Apr 4, 2013

Geir tested a few very old (like 25-30 y.o.) Dyneema slings for me, and as 20kN said, they all failed at loads within spittin' distance of their rated strength.


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By Tom Mulholland
From #1 Cheese Producing State!
Apr 4, 2013
Whiskey-a-Go-Go

20 kN wrote:
3. Use the mV/V value located on the load cell certificate. The third option is by far the most accurate option and it is pretty much the standard for programing conditioners/ indicators.

It's been a few years since I dealt with load cells, but I don't think this works for calibrating the cell. Yes, the mv/V slope should be consistent with the factory value, but there can be some residual voltage readings at zero load, which is the point of calibrating.

But, if you can find 1 known weight, or better, 2 known weights, you could construct the load/volt line along with the zero-load reading, and have a decent calibration. Better if you can use weights in the intended loading range (i.e. don't calibrate with 5 pounds if you're going to test forces of several tons).


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By Chris Vinson
Apr 4, 2013

Send em in, we'll break stuff.


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By Aric Datesman
Apr 4, 2013

Couple more thoughts while I finish lunch...

1. I forgot about Rich Delaney doing testing down in Australia. Great guy and is the one behind the Rope Test Lab group on FB, but dunno if they'd be interested in this as they're in the middle of a HUGE project that might change roped-access work standards world-wide (and are trying to make a go of being a for-profit test lab). Easiest way to get a hold of him would likely be the FB group. On a side note, I sent them most of my test gear a while back to help supplement what they had, since I have no interest in getting back I to public testing and no longer needed that gear.

2. Mattm- as Sayar suggested, there might be a way to program the mv/v spec directly into the conditioner. Barring that, you're stuck with either using another setup or known loads. I suppose since you're using a portapower you could back into a ballpark reading by way of a pressure gauge on the hydraulics and piston area, but that's far from ideal.

3. Also Matt- does the portapower pump work but just not the pullback ram? If so, you've got a bad ram and it might not be worth fixing unless it's one of the big name brands. Other thing to watch for is putting a portapower pump on a larger cylinder... Simply not enough reservoir volume for it to work.

4. Rob- I pitched something similar to the AAC years back, and they had no interest. Doesn't mean you shouldn't try them though.

5. Tom's spot on with calibration. If you're expected measurement is 10kN, calibrating it with known 9.9kN and 10.1kN loads will do a much better job than relying on the mv/v value. But it's more work, and some conditioners allow for defining correction factors to correct for any nonlinearities in the strain gage along its range.

Anyway....


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By Aric Datesman
Apr 4, 2013

Ah, one other thought.... Pulling soft goods is a PITA due to the amount of stretch. As in I've seen single length nylon runners add an additional foot or two in length before breaking. Even with starting out taught I've maxed out stroke on my 36" pullback ram on occasion...


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By Tom Mulholland
From #1 Cheese Producing State!
Apr 4, 2013
Whiskey-a-Go-Go

Aric Datesman wrote:
Ah, one other thought.... Pulling soft goods is a PITA due to the amount of stretch. As in I've seen single length nylon runners add an additional foot or two in length before breaking. Even with starting out taught I've maxed out stroke on my 36" pullback ram on occasion...


And a note to add about that - polymers exhibit different breaking strengths depending on the rate of testing. I'm not sure off the top of my head how nylon acts (or for that matter, woven nylon fibers), but in general the difference can be quite large between a slow testing speed and a rapid testing speed.

That's important, as data taken with a slow testing speed just isn't relevant to normal loading/failure conditions for nylon slings in climbing. Maybe if you're using your nylon slings to pull trucks out of the mud...


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By Bryan Ferguson
From Castle Rock
Apr 4, 2013
Marvin and Greg scoping Crow's Heads Spires - snowed out on fall 1982 attempt

We pull test here at FPS Editions. We just relocated to Castle Rock, Colorado a week ago and are getting set up. We do static/slow pulls with winch and scale of knots and systems. FPS is an organic start up concerned with teaching and learning in challenging environments including mountaineering and other outdoor and industrial pursuits. We like to use used gear for pull testing because we are interested in the end user experience. We’d welcome your “mid-life” soft goods for testing. Please email me for more info.


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By Jon Hillis
Apr 5, 2013

I have got a couple old cams that I bootied along with a slung hex and i think some nuts. Been looking to get rid of them, one of you guys want to pull them too?


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By 20 kN
From Hawaii
Apr 5, 2013

Tom Mulholland wrote:
It's been a few years since I dealt with load cells, but I don't think this works for calibrating the cell. Yes, the mv/V slope should be consistent with the factory value, but there can be some residual voltage readings at zero load, which is the point of calibrating. But, if you can find 1 known weight, or better, 2 known weights, you could construct the load/volt line along with the zero-load reading, and have a decent calibration. Better if you can use weights in the intended loading range (i.e. don't calibrate with 5 pounds if you're going to test forces of several tons).

Using the manufacturer-supplied mV/V value is the most accurate way to program a conditioner, and it is the method recommended by Mantracourt. You can read more about this process in the user manual for this conditioner: www.mantracourt.com/products/signal-converters/usb-load-cell>>>


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By Red
From Arizona
Apr 5, 2013
Cobra Kai

This guy does pull tests.


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By Aric Datesman
Apr 5, 2013

20 kN wrote:
Using the manufacturer-supplied mV/V value is the most accurate way to program a conditioner


Certainly the easiest, but not necessarily the most accurate due to the potential for nonlinear response of the strain gage. But in the end it's all the same... The single/double weight is merely a way to back into the mv/v value by dividing the mv response by the excitation voltage. With certified weights bracketing the target measurement, the 2 weight calibration will be more accurate but who wants to go to that trouble when simply get a load cell that includes the nonlinearity data and use a conditioner that can correct for it?


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By Aric Datesman
Apr 5, 2013

20 kN wrote:
Using the manufacturer-supplied mV/V value is the most accurate way to program a conditioner


Certainly the easiest, but not necessarily the most accurate due to the potential for nonlinear response of the strain gage. But in the end it's all the same... The single/double weight is merely a way to back into the mv/v value by dividing the mv response by the excitation voltage. With certified weights bracketing the target measurement, the 2 weight calibration will be more accurate but who wants to go to that trouble when simply get a load cell that includes the nonlinearity data and use a conditioner that can correct for it?


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By 20 kN
From Hawaii
Apr 6, 2013

Aric Datesman wrote:
Certainly the easiest, but not necessarily the most accurate due to the potential for nonlinear response of the strain gage. But in the end it's all the same... The single/double weight is merely a way to back into the mv/v value by dividing the mv response by the excitation voltage. With certified weights bracketing the target measurement, the 2 weight calibration will be more accurate but who wants to go to that trouble when simply get a load cell that includes the nonlinearity data and use a conditioner that can correct for it?

Sure, well I meant the most accurate of the three options. My understanding is that the mV/V value on cal certs is measured at full load, so you do have two points: zero lbf and full load. But you are correct that if one wanted to account for the non-linearity curve the use of bracketed weights along the entire range of the cell is a better option. But really, I suspect we are splitting hairs. The non-linearity curve of my class III cell is 0.85 lbf maximum for a 5,000 lbf cell, which is quite linear IMO. At the lower end of my cell's range, if I hang a weight on the cell and set the conditioner to 10 Hz or slower my indicator can achieve an accuracy of around 0.2 lbs.

But if one were to require greater accuracy, NTEP class I and II cells offer even better accuracy rates as I am sure you know. However, I am not sure there is a practical application for something that precision in this field. I dont know if NTEP I s-beam cells exist, but if they do I would envision they would be fairly pointless unless you plan to weigh a cup of flour with a 3,000 lbs cell. :P


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By Aric Datesman
Apr 6, 2013

Yup, splitting hairs. But ones that show the comment that the mv/v value method being the most accurate is incorrect.


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By Locker
From Yucca Valley, CA
Apr 6, 2013
...

"Anyone do pull tests?".


Not as often as when I was a young teen.


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By Helas123
From Ontario/California
Mar 25, 2014

I think you need to use load cells for pulling process. Load cells are effective products which are commonly used in these days and easily available in market or you can check latest prices of load cells from southoceansensor.com .


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