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-   -   Hydraulic "scale" (https://www.shopfloortalk.com/forums/showthread.php?t=49216)

RED caddy 03-18-2018 11:53 AM

Hydraulic "scale"
 
Back when I was a pup, in an old popular mechanic's magazine, I found a set of plans for a hydraulic scale. I built/machined one and used it to measure tongue weight on my various trailers and even individual static wheel weights on race cars. No calibration required because, IIRC, according to the original plans, the only variable was oil temperature/viscosity, and that was not easily measurable.

Over the years, I've lost it and a second one I fabricated. The one from the original plans read up to 1500 Lbs. (gage limit) It was a very simple design, a piston with an area of 1 inch, 2 sealing "O" rings and a cylinder with a total capacity of ~2 OZ of mineral oil, (likely because it was kind to the "O" rings of the day) and a threaded port to accept an adapter and the 1500 Lbs. gage.

As with so many things I search for lately. I can't find something like this commercially available, or even a set of plans. (yes, I looked in the archives of PM)

I want to use this idea, but expand the weight limit to 24-2500 Lbs. use a bigger diameter gage face and, I assume better, or at least higher rated, seals with the higher reading gage.

What I need to know is what type / size/ composition "O" rings or hydraulic seals do I need to update this design, and any other point's I'm missing.

I know you guy's love to play "what if" so lets go "pencils up"

Thanks RED

digr 03-18-2018 12:11 PM

Here ya go

RED caddy 03-18-2018 12:41 PM

WOW, nice work Dig'r. Thanks.

When ya get time, PM me a small wizards portion of Google Foo, mine seems to have escaped. (ya didn't have to make it look so easy, ROFLMAO)

Now that we have a proven set of prints, lets get to work on the scale up plans. Wizards hat's in place, ready... GO

RED

digr 03-18-2018 12:53 PM

1 Attachment(s)
Found it in no time, went to google books and searched for "Popular mechanics" and opened the first one that came up, then to the left of the page there is another search box where I put "build a scale", then clicked on " search all issues" and it was the first one that came up.

RED caddy 03-18-2018 01:08 PM

OH HELL, "build a scale" would never have occurred to me, I found the page to search from, but no joy.

Thanks again

RED

greywynd 03-18-2018 01:20 PM

If you have a small enough cylinder already, you can use it, just need to figure the area and crunch the numbers to figure out a scale for the gauge.

I’m thinking a pancake cylinder from a hydraulic portapower type set and a pressure gauge could fit the bill.


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RED caddy 03-18-2018 01:33 PM

Well, we already know the correct bore size (1.128") and stroke does not seem to be a big deal in this case. I was just concerned that 2 "O" rings might not stand up to 24-2500 PSI and a better seal setup might need to be brought to bear.
What do you think?

I have a pancake cylinder lying around, might have to open it up and check the bore size.


Thanks, RED

LKeithR 03-18-2018 01:36 PM

Quote:

Originally Posted by RED caddy (Post 708093)
...Now that we have a proven set of prints, lets get to work on the scale up plans...

To reach a higher range you don't have to "upscale" anything. With a piston area of exactly one inch that scale will read one pound on the gauge for every pound of pressure applied. The trick is to find a gauge with a large face and fine enough graduations that you can make some sense of them. There are some nice digital gauges out there that would work perfectly for this application.

Digital Gauge

A quick comment on the O-ring groove. While it is "correct" to put a 5 degree taper on the sides of the groove I have made lots of grooves with straight sides--for low pressure stuff I don't think it makes that much difference. Nowadays there are lots of insert tools with the right profile so it's not much of an issue anymore. And, of course, you HSS holdouts can always grind your own...:D

LKeithR 03-18-2018 02:08 PM

Quote:

Originally Posted by RED caddy (Post 708099)
Well, we already know the correct bore size (1.128") and stroke does not seem to be a big deal in this case. I was just concerned that 2 "O" rings might not stand up to 24-2500 PSI and a better seal setup might need to be brought to bear...

Good point...hadn't thought of that. For 2500 psi you'll need to go to a proper cup type seal. If you do decide to mess around with a larger bore it's handy to remember that "doubling" the diameter of the bore gives you "exactly" 4 times the surface area...

USMCPOP 03-18-2018 02:24 PM

Here's a scale made from a hydraulic bottle jack:

http://www.shoptalkforums.com/viewtopic.php?t=125881

Here's a guy who added a gauge to a jack so he could measure force on his press. He had to add a port for the gauge. (I thought his mention of a mod to allow upside down pumping was interesting.)

https://www.youtube.com/watch?time_c...&v=ZBmxkWK_OFA


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