how much flow thru a sae8 fitting

[oldnslo]

The good news is, you get the chance to be wrong AGAIN Just kidding, from a guy who gets LOTSA chances at that distinction

Check this out

http://www.discounthydraulichose.com/v/vspfiles/downloadables/thread_guide.pdf

Look at the chart on page 8, straight thread O-ring fittings (SAE or ORB)

SAE 08, THREAD size is 3/4-16, nominal PORT size is 1/2" - so at least for SAE, it appears that the dash # may be actual port usable diameter (in 1/16" increments - 08 = 8/16, = 1/2")

Now I gotta get off my tush and go work on my brush fork project - I'm sure it'll take at least 3 minutes to "be wrong at least one more time (in the next half-hour, that is ) ...Steve

The - 8 is for reference purposes. in tubing it would the OD or 1/2" and ID would change depending on wall thickness. With hose it would normally be 1/2" ID. Through hole in fitting has nothing to do with this reference number.

 

[BukitCase]

Sorry, I'd thought I had clearly limited my statement to that particular case, as in a "happy accident" - just re-read, and it didn't come out that way.

I know about the dash #'s ACTUALLY being the # of 1/16" of NOMINAL fitting size, and that this depends on the TYPE of fitting/hose/tube/pipe whether this measurement is inside, outside, "used to be" (pipe), or whatever -

I'll try to be more complete in answers, therefore less confusing (maybe) :laughing: ...Steve

 

[muddstopper]

OK, now you have me totally confused. Is or isnot the inside dia of a sae8 fitting 1/2in?

 

[J_J]

I was hoping Ken would chime in here and set us straight about the true inside diameter or a fitting or tubing, etc.

 

[BukitCase]

Well, Ken's not here yet so I went out to the shop and measured a few fittings I ordered from DHH - 3 different fittings with SAE 8 on one end, all were ACTUAL bore size of 3/8" - so I checked a couple of -06 SAE's, and they measure 5/16".

Sorry, I made the mistake of assuming - apparently, "nominal" in fittings means about the same as it does in dimensional lumber - nobody here is likely to believe that a 2x4 measures 2 inches by 4 inches - although they DID once upon a time.

I WILL say that these (DHH) fittings seem to have a REALLY thick wall - so maybe another brand might have a larger bore, I don't know.

Sorry for the confusion - looks like if you want a true 1/2" path you'd need to go at least to a -10 size... Steve

 

[J_J]

Did you happen to check the orifice in a 1/2 in QD?

 

[oldnslo]

I believe Parker fitting catalog shows the the thru hole size on their fittings. Other manufacturers may as well. Look at a typical hose end. If the ID of the hose is 1/2" and the fitting barbed end goes inside the hose it has to be smaller. Fittings are almost always the smallest diameter of any plumbing component. The main concern is to try and limit how many fittings, elbows, etc. are in any given system where there is going to be constant oil flow. Example on a log splitter would be. Pump Inlet, pressure line to directional valve, return line from directional valve. Cylinder lines should be sized to try and maintain a reasonable velocity but since they are infrequent flow cycles a slightly higher pressure loss usually does not create enough heat or back pressure to adversely affect the operation of splitter.

Typically QD's are the worst device in a system for causing pressure drop. This usually is not a concern for running a cylinder in and out like for normal FEL use. potential problems arises when they are used for continuos flow functions on CUT's since most CUT's do not have the oil capacity or cooling capacity to handle full flow through the QD's for extended periods of time.

Back to the OP question. I would NOT worry about the 3/4-16 ORB ports on your cylinder. Use a directional valve large enough to handle the flow and run large enough pressure and return lines to handle the pump flow. Use step size fittings to go at least - 10 hose on the rod end and -12 on the cap end on the cylinder. Your splitter should operate just fine.

 

[J_J]

Here is some data from Safeway on their QD .

I refer you to page 20.

According tho the nomogram, 1/2 in can flow about 12 GPM at 25 fps.

Unless the tractor owners uses 10 fittings per hose , he probably has nothing to worry about.


A couple of L's couple of T's, one or two QD's should be fine.

 

[BukitCase]

oldnslo makes several valid points - like most things, the KISS method is almost always better - but sometimes you need an "evil device" or three to make things usable (like QD's, durnit...

JJ, as mentioned earlier I have several sets of DHH's version of 1/2" "AG" style QD's, here are my observations -

If all the crap that's inside were gone, you'd get a 15/32" dia. flow path - WITH said crap, (and this is a "SWAG", as I call it - Scientific Wild Assed Guess ) - MAYBE somewhere around 1/4".

I have a couple of things with older, non-import QD's of a couple different types - they don't fare much better.

The ones I have been talking about have a "three-legged spider" inside for the ball spring to push against, and a type of retaining ring I haven't seen before, and therefore haven't either bought or invented a tool for - so we will NOT be getting a "dis-assembly report"

Near as I can tell from cautious observation - with the two halves locked into each other, their respective check balls appear to move away from their seats about 3/16" - so in the center, there's still about 1/4" dia. still blocked -

A 15/32" dia. hole has an area of 0.1726 sq. in.
Subtract 1/4" dia. center, area of 0.049 sq. in.
Leaves an area of 0.1236 sq. in.
Which equates to a circle of dia. 0.1983" - which is just a bit larger than an equivalent 3/16" diameter path.

Since circle areas are related to a square root function, half diameter = 1/4 the area - so you would be getting less than 1/4 the flow thru these QD's than you would thru a plain 1/2" hose, assuming the same pressure -

One of the problems with that assumption is that the restriction of the QD will cause a LARGE pressure drop across the QD, and the larger the pressure differential the greater the flow - so to me, it's likely that PART of the "problem" may offset PART of the flow drop - been a while since I needed to "cogitate" on this, so I may be more than slightly rusty

To FURTHER muddy the waters, let's assume that ONE of the halves of a QD pair has a WEAKER spring than the other - That condition will cause the two check balls to NOT be evenly pushed back from it's seat - this would make things even WORSE. (Like we needed THAT...)

Now I'm starting to wish I'd never opened this can of worms - halfway considering a redesign of some of my stuff to just do away with QD's - Instead, just shut 'er off, normalize pressures and hook-unhook with JIC's and a (quickly used) pair of wrenches... Steve

 

[J_J]

The manufacturers say it works, and I don't have a test bench, and I don't ever measure the fps of fluid flow. It will probably vary at each fitting anyway, so the flow in GPM will vary, and the pressure will change.

Yea, why did you open this can of worms?