Tractorsport Flowbench Forum Archive

Posted: **Tue Dec 09, 2008 6:44 pm**

Would be an interesting comparison checking all the fluids against each other. The more I hear Rick talk about the DOT5 the more I like it. Never gave it a thought.

Posted: **Tue Dec 09, 2008 7:21 pm**

Posted: **Tue Dec 09, 2008 7:24 pm**

Posted: **Tue Dec 09, 2008 7:29 pm**

Also on the DOT and I don't know if it plays a part anymore, but we once put DOT in a spitfire we raced and it had real rubber in the brake system and the DOT caused it to swell up. We had to find some Girling special brake fluid for go with our positive ground electrical system. :;):

btw Do you know why all Brits drink their beer warm?

They all own Lucas refridgerators.

John

Posted: **Tue Dec 09, 2008 7:44 pm**

There are more than one way to attack the problem and you are doing it a different way that's all. I personally would not want to recalculate my plates and would sooner match my incline to my plates. I like to work with round numbers ie a 10", 12", 16" DP and set my incline to match that.

Just different ways to go about the same end result

Posted: **Tue Dec 09, 2008 7:55 pm**

John,

I am talking about DOT5 this is pure synthetic silicone fluid smells good and safe on paint, some people in parts of our country use it for Tire dressing to get that SHINE ???.

Comes in Nice Lavender Purple color :;):

Rick

Posted: **Tue Dec 09, 2008 8:51 pm**

Posted: **Tue Dec 09, 2008 9:16 pm**

I just found the MSDS for DOT 5 Silicone brake fluid. Looks like a great thing to use for the flow bench. SG on this one I found is .958 and theirs is blue.

I have attached the MSDS in pdf form. I want to caution everybody, ***DO NOT USE ANY OTHER BRAKE FLUID as in DOT 3 or 4 **** It is highly toxic and can shut down you central nervous system. DOT 5 seems to be fine looking at the MSDS.

THANKS to Rick.

John

Posted: **Wed Dec 10, 2008 2:52 am**

awright, so, if I "get" this right, if I used DOT 5 fluid the scale correction to water would be .015 per inch. Small enough to be ignored, or, a new scale could be made. Corrected, 28" water would be 28.425" DOT 5, 36" water would be 36.548" DOT 5.

Also, tube rise vs. well drop doesn't affect scale, it affects delta p and orifice size

Am I getting this yet?

Posted: **Wed Dec 10, 2008 12:57 pm**

Mopar, I'm not sure where you got .015, but I saw that Rick says "tap water" is actually about .985 SG. DOT 5 is .958 so the correction is .044 in/in. but you have it right in principle. The tube rise/well drop question is true only for ratiometric scales (% flow), not vertical scales or inclines reading in inches.

John (et al), I have been thinking about the "subtraction" vs division question and I MAY have an answer. I just couldn't put it down so had to figure something out! In advanced design engineering (my field) we have a lot of quick and easy number crunching approximations (also called sanity checks). One of them is, FOR SMALL NUMBERS (those close to 1.00), the difference (subtraction) is nearly the same as the reciprocal (division). If I was looking at a .99 specific gravity, the difference would be .01 while the recip would be .0101. At .95, the numbers would be .05 vs .0526 while at .9 they become .1 vs .1111. The further you get from 1, the less accurate the approximation becomes. At 1%, the error is about 1%, at 5% the error is a little over 5% and at 10%, the error is 11+%, but at a .5 SG, the error is 100% (.5 vs 1.0). How far you go depends on how much error you can live with. Could be what the other thread was doing? -- Doug

Posted: **Wed Dec 10, 2008 2:26 pm**

Posted: **Wed Dec 10, 2008 3:08 pm**

Slracer--I messed up. I transposed numbers, to get .015. you're right, .958 = 1.0439, which makes 28" water = 29.229" DOT 5, or 36" water = 37.58" DOT 5

thank you for the clarification on well drop for the vertical gauge.

so the question becomes- How much correction math do you want to do? or, How much error in your bench can you live with? Seems there's some error to be accounted for even in "straight" water.

Posted: **Wed Dec 10, 2008 4:38 pm**

John, Technically, the SG of water is 1.00 only at 4*C (about 41*F) and is for "Pure" water. At 60*F, it is lower (.983 by my source) and at 80*F it is down to .975. That same source shows "Tap water - average" is lower (.9999) at 4*C but up to .975 at 80*F. It just says the temp of the test water is more important than the source, but still not worth messing with. If you really want to go crazy with this train of thought, what about the coefficient of thermal expansion on your scales? :p

Mopar, I made my Excel spreadsheet with corrections for well drop (due to a smaller than a Tony suggested diameter ratio) and included an input for SG in case I ever want to change. Right now, I don't want to clean up an overpressure of anything but water so will get some experience before changing to something else. Besides, my shop is heated! :laugh: An old version of the spreadsheet is here:

This hasn't been updated with my new variable geometry changes which removes some of the other corrections. That will come soon after I finish calibration.

Doug

Posted: **Wed Dec 10, 2008 6:27 pm**

Doug,

That is the site i looked at and my point exacly, I think we could be spitting hairs.

Rick

Posted: **Wed Dec 10, 2008 7:26 pm**

Rick, I think so too! Well drop if it is a bigger number, and whatever fluid you want! Trying to get the pitot bench sorted out again after a long layoff. Hope to have it all setup for first quarter of 2009. -- Doug

Tractorsport Flowbench Forum Archive

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