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Old 11-16-2013, 02:08 PM   #51
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While i agree that keeping the Teflon tape away from the end of the threads is important, one wrap may not be enough to get a good seal. Most of the recommendations I've read recommend 3 wraps. You could use a few more to change the gauge face orientation.

I don't think the lock nut would work since it might allow the gauge to face the right way, but the threads not tightened enough to prevent leakage.
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Old 11-16-2013, 04:25 PM   #52
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"Clocking" fittings is certainly one of the annoyances of tapered pipe threads.

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Originally Posted by gbaglo View Post
You mean Teflon tape?
"Plumber's tape", "PTFE tape", or "thread seal tape"... there is no Teflon tape. But we know what you mean!

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I was warned by Sherline not to apply it too close to the end of the threads or fragments can end up in the oil and plug the valve.
Valve? In a Sherline scale? Do you mean the gauge? Bits could also mess with the O-ring seal. I didn't think there was a valve in these things.

Whatever might get messed up, I wouldn't worry about it too much: this is a static system, without significant flow of oil to carry bits.

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I'm going to try to apply the minimum, maybe one wrap.
Or go the other way and pile on an extra wrap (on top, not further along the thread) - whatever results in the thread getting tight at about the right position.


And I agree with everything Jon said.
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Old 11-16-2013, 04:25 PM   #53
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Sherline testing

Sherline Gauge Testing
Testing of the Sherline Hydraulic Tongue gauge was done in a calibration lab atmosphere under controlled conditions. Equipment used was a TiniusOlson system that was certified from 300 lbs to 20,000 lbs with a tolerance of +/-1% of reading. The system uses load cells for measurements and had a pre-load of 90 lbs. The load cells were exercised throughout the testing range prior to use per standard operating instructions. The Sherline was placed within the load frame, (capable of 20,000 lb testing) on a solid steel surface. The compression cylinder was part of the load frame, again, capable of testing 20,000 lbs. The whole setup is mounted to a thick concrete floor (we’re talking feet here) which is rated for some level of earthquakes. Using this system prevented any and all vibrations with no side loads being applied. The compression cylinder can be controlled using a motor or hand wheel. I used the hand wheel for its fine movement capability. I made 5 runs, both applying and relieving pressure. Each run took less than 3 minutes to perform, and the gauge was always returned to zero between runs. From those 5 runs I calculated the average and the deviation at 100 lb increments starting at 300 lbs (the certified lower limit of the test equipment.

Unless otherwise stated, when a manufacturer provides a tolerance, (2%) this tolerance is of full scale. In this case it’s 2% of 1,000 lbs, or +/-20 lbs. Sherlines’ statement that the gauge will provide a tighter tolerance in the middle of the scale is correct, but they don’t state what that tolerance is. In this case we have to go with industry standards. On an analog gauge, only the 10% to 90% range of the scale is expected to meet the stated tolerance. So this scale could be certified from 100-900 +/- 20 lbs.

Testing: Applying Pressure Relieving Pressure
Sherline TiniusOlson Difference Deviation TiniusOlson Difference Deviation
300 305 5 30 282 18 20
400 409 9 11 383 17 15
500 511 11 10 484 16 15
600 619 19 12 588 12 10
700 721 21 14 692 8 5
800 820 20 16 797 3 10
900 921 21 18 903 3 5
1000 1027 27 20

Summation: In my opinion, this scale is uncertifiable to the stated specifications. The uncertainty ratios would normally be calculated, and guard banding applied, but with deviations so great, this scale would be rejected.
I was hoping for more consistent results so that I could apply known errors to my own tongue weight measurements, but with the large deviations observed, an accurate measurement would be difficult. The production/quality lead for Sherline told me that this gauge was tested just before sending it to me, so it will be interesting what they say when I give them this information.

Sorry for the legibility issues, I tried Word, then Excel embedded in Word, and still can't get columns to line up. The first column is the Sherline reading, second the TiniusOlson reading, third the difference, fourth the deviation in the 5 tests, fifth the TiniusOlson readings relieving pressure, sixth the difference while relieving pressure, seventh is the deviation in the 5 tests while relieving pressure.
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Old 11-16-2013, 05:02 PM   #54
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Or go the other way and pile on an extra wrap (on top, not further along the thread) - whatever results in the thread getting tight at about the right position.


And I agree with everything Jon said. [/QUOTE]

Thanks guys. The extra wraps of plumber's tape ( not Teflon ) appears to have done the trick. Learn something every day.

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Old 11-16-2013, 05:24 PM   #55
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Quote:
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Sorry for the legibility issues, I tried Word, then Excel embedded in Word, and still can't get columns to line up.
Tom
A mono-font would normally work, but the software strips out extra spaces.
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Old 11-16-2013, 05:25 PM   #56
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Testing of the Sherline Hydraulic Tongue gauge was done in a calibration lab atmosphere under controlled conditions...
Excellent!

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Originally Posted by TAfraser View Post
Testing of the Sherline Hydraulic Tongue gauge was done in a calibration lab atmosphere under controlled conditions.Sorry for the legibility issues, I tried Word, then Excel embedded in Word, and still can't get columns to line up.
No apologies required, Tom! This is always a challenge in recent versions these forums. You can try padding a table out with spaces and forcing a monospaced font, but even that doesn't work well, especially if you include headings.

I pasted the information into a spreadsheet (in this case, a Google Doc in Google Drive: Sherline Tongue Weight Scale), then saved it as a PDF file and attached to this post. I hope I got the column arrangement as intended!

I see that it typically displays the offset which we might expect as a result of seal resistance, reading low while applying force and low while reducing force... by significant but manageable average amounts. It makes sense to take readings only while increasing load (lift some load off with tongue jack, change trailer configuration, set back down on scale), although there's no need to take the load off entirely.

The average difference (essentially, error) seems acceptable to me, but the deviation is disappointingly large.

It would be interesting to know how much of this is due to the hydraulic cylinder itself (such as the o-ring sticking), and how much is the pressure gauge. It would be completely unreasonable to expect anyone to do this, but it would be informative to see the two tested separately, testing force-to-pressure and pressure-to-reading independently.
Attached Files
File Type: pdf Sherline Tongue Weight Scale - Test Results.pdf (42.3 KB, 10 views)
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Old 11-16-2013, 05:44 PM   #57
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Hi Brian, I would have tested the gauge separately, but the lab only had equipment that could take the gauge up to 100 psi. I would have had to interrupt a production line in order to access appropriate equipment. Didn't think they would appreciate that. I agree with you on the very disappointing deviation numbers. If the deviation was better I would just apply the offsets to my measurements and be done with it. Now, I think a talk with Sherline is appropriate. It was also a surprise that the center of the gauge wasn't more accurate then the rest. It indicated a linear progression. Could it be that their cylinder isn't held to tight enough tolerances for a one-to-one conversion from hydraulic pressure to psi?

Nice job on the spreadsheet attachment.
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Old 11-16-2013, 05:53 PM   #58
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Just curious. What gauge do you have 0 - 1,000 or 0 - 2,000.
I replaced the 2,000 gauge so it would be easier to read and be closer to the middle of the gauge for accuracy.
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Old 11-16-2013, 06:43 PM   #59
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I have the 1,000 gauge
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Old 11-16-2013, 07:26 PM   #60
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To state what apparently is not the obvious, incorrect use of the scale previously leaving weight on it instead of following the directions to remove all weight after each weighing, may have affected it. Plus anything else done wrong, not having followed the basic directions. Any testing afterward is, therefore, of no consequence.

We have the 1,000 and it works just fine.
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