Manometer advice

[slufkin]

My son and I are building a simple orifice style bench to test kohler command heads for his pulling tractor.
I have read lots of posts about manometer fluids but I'm still not quite getting it. My shop freezes in the winter so I would like to use something like brake fluid or oil or something, that way I can eliminate the evaporation and the freezing problems at the same time.
What I can't understand is how do I come up with accurate scales for both vertical and inclined manometers?
I am hoping to test at 28", but I am just using my shop vac for starters, not sure if we will get there.

[Brucepts]

Marvel Mystery Oil specific gravity of 0.876 so all your scales would be based on 1"=1.143" using that fluid

[Tony]

Or you can just test the fluid of your choice and compare the rise, to the rise of a reference water manometer fed off the same pressure differential.

[jfholm]

Once your manometer system is made it should be pretty well sealed. On mine the evaporation factor was nil on the inclined manometer. Just design the the reservoir so it is easy to open and top off. In really cold areas you can just run antifreeze and water. We did that on my friends bench because his shop was not always heated. Worked fine.

But I do love the smell of MMO and red is a cool color.

John

[Old Grey]

You should be able to work out the specific gravity of any fluid by weighing it - 100cc on a sensitive scale -.

There are spreadsheet to work out scales somewhere around here - look in Useful Programs & Spreadsheets for Flowbenchin'

[slufkin]

Thanks Bruce.
MMO will work perfectly. I have a few more questions if you don't mind...

Do you all recommend a U tube for test pressure or a reservoir? I was just going to do a U tube because it looks a little simpler.
If I do go U tube, then I will mark it as you stated divided by two correct?

When I do my inclined scale, does it care what the fluid is? If so then do I just use the standard scale generator and multiply by the figure you gave me for that one too??

Sorry for the dumbies, but this is all new to me. This site is great, but there is so much info that it is a bit overwhelming.

Thanks All.

[Tony]

If I do go U tube, then I will mark it as you stated divided by two correct?

Twenty eight inches test pressure will make one manometer leg rise 14 inches, and the other manometer leg fall by 14 inches.

When I do my inclined scale, does it care what the fluid is?

Same scale for any fluid, any scale length you wish to make it will work fine.

What matters with the incline, is how much higher the high end is above the low end.
With oil, the fluid tends to rise further for any given pressure, so you set the incline steeper to compensate.

Bruce's orifice plates are calibrated to work at 16 inches water rise, so with a water manometer, the 100% flow mark would be set to be exactly 16 inches higher than the 0% flow mark.
That would apply to any length of sloping manometer tube length you plan to use.

With oil, you will need to set the high end higher by a few inches, making the slope steeper, but otherwise the same tube, with the same 0% to 100% flow scale will work.

[Brucepts]

On your incline scale make the slope so you can adjust it up and down so you can calibrate your flowbench. As Tony said my plates are rated at 16" DP but you might end up with your rise below or above 16" to dial the calibration in.

Rocco's spreadsheet will let you calculate out what you need but in the end you want to have some way to tweak your incline scale if need be.

[slufkin]

Thanks guys.
So it would be reasonable to start with the inclined scale around 32-34" long with adjustable angle and I will go from there right?
I think I will stick with the U tube for DP. I think I understand how to adapt the scale to work with Marvel MO...

Thanks for all the help..
I hope someday to upgrade to some of your automation, but for now, we just want to get something up and running to play with. My son is 17 and interested in learning.

[jfholm]

I love my digital stuff, but I am also a very visual person. The water manometers are a great tool for teaching because you can see them and how they work. It really does help learn the concept.

John