Air Couplers: HIGH FLOW low flow vs LOW FLOW low flow.

[Stedlin]

(For informational purposes only)
I wager most air tool users are not aware of this.
It's a fact that some standard couplers have much better flow than others
using the same M style plugs.

For example:

Conventional M style coupler:
41 PSI pressure drop with 1/2" impact free running at 90 PSI.;
(some couplers or this style are better and some are actually worse.)

Stedlin Quick Coupler with same M style plug.
13 PSI pressure drop.

I am sure that many users that switched to the so called HiFlo style did so because unknown to them they were using "Low FLow low flow couplers".
A 40 PSI pressure drop from one coupler and plug is rather startling but it is a fact as the image shows.
To be fair, the Stedlin Quick Coupler shown is not the only coupler that has this much flow with an M style plug.

 

[DeeKay]

I might be interested if they weren't aluminum.

 

[Stedlin]

I might be interested if they weren't aluminum.

We use aluminum because of the weight even though it costs us more.

 

[matt_i]

What if you keep the line pressure the same instead of regulating the line pressure down so the secondaries are equal?

Maybe you did. It seems improbable that the secondary pressures are less than 1psi difference unless you regulated it that way.

 

[Stedlin]

What if you keep the line pressure the same instead of regulating the line pressure down so the secondaries are equal?

Maybe you did. It seems improbable that the secondary pressures are less than 1psi difference unless you regulated it that way.

For this particular test I regulated the pressure to 90 at the tool to achieve a similiar flow rate.

 

[matt_i]

If we use an Ohm's law analogy V=IR, it seems like you chose to drop V (the forcing pressure) in order to show a drop in R.

Reducing the forcing pressure by ~25% is going to have a difference, methinks?

 

[DeeKay]

We use aluminum because of the weight even though it costs us more.

Not trying to tear apart your product, but a 1/4" steel industrial coupler and plug weigh what a few ounces? I just don't really see the benefit of saving an ounce vs the sacrifice in durability. That's just my Opinion.
I've had aluminum ones before just because that's what the store happened to have in stock and the tip of the plugs always got beat up which in turn ends up tearing up the seal in the coupler.

Where did you get the improvement in flow? The coupler design or the plug? I would guess the coupler since there isn't a whole lot that could be changed in the design of the plug outside of boring the hole out more.
If you are regulating the pressure at the tool to achieve a similar flow rate, how did you meter that flow rate? Genuinely curious

 

[Stedlin]

Not trying to tear apart your product, but a 1/4" steel industrial coupler and plug weigh what a few ounces? I just don't really see the benefit of saving an ounce vs the sacrifice in durability. That's just my Opinion.
I've had aluminum ones before just because that's what the store happened to have in stock and the tip of the plugs always got beat up which in turn ends up tearing up the seal in the coupler.

Where did you get the improvement in flow? The coupler design or the plug? I would guess the coupler since there isn't a whole lot that could be changed in the design of the plug outside of boring the hole out more.
If you are regulating the pressure at the tool to achieve a similar flow rate, how did you meter that flow rate? Genuinely curious

The main reason for plugs being manufactured from steel has to do with the wear caused by the locking balls. The Stedlin couplers use 8 polymer balls that do not damage aluminum plugs in addition to allowing low friction free rotation.
The couplers and plugs are made to very tight tolerances on CNC swiss machines to minimize play for extended lifetime.

The increased flow comes from the Coupler body itself. The tests shown are both using the same M style industrial steel plug with 3/16" bore size.

The flow rate is simply a function of the pressure drop across the impact tool which is specified at 90 PSI.

 

[Stedlin]

What if you keep the line pressure the same instead of regulating the line pressure down so the secondaries are equal?

I made this video with the upstream regulator set to 135 PSI.

Flow test

 

[sberry]

I a so used to using a better plug I dont know the difference. A lot of guys work a long time with regular **** too.

 

[bsaint]

So basically youre telling me to run the airline at +17 psi before the gun?


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[mhejl]

How about posting a comparison to V-style couplers/plugs which are probably more common than the M-style? I have too many to replace with Stedlins - it'd cost me a small fortune even with the promo codes.

That said, I definitely recommend Stedlin QuietHose adapters and orbitals. I have QuietHoses on every one of my hoses. The orbitals have better range than any of the others I've tried (but than can "bite" your hand because of this).

 

[Stedlin]

How about posting a comparison to V-style couplers/plugs which are probably more common than the M-style? I have too many to replace with Stedlins - it'd cost me a small fortune even with the promo codes.

That said, I definitely recommend Stedlin QuietHose adapters and orbitals. I have QuietHoses on every one of my hoses. The orbitals have better range than any of the others I've tried (but than can "bite" your hand because of this).

I did post a comparison to the V-style and here it is again.
coupler flow comparison

One and a half PSI difference between the Stedlin and the V style. The Stedlin with full flow plug is virtually the same as the V in this high flow test.

 

[Stedlin]

So basically youre telling me to run the airline at +17 psi before the gun?
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NO.

Air impact tools produce their rated torque at 90 PSI pressure. That means 90 PSI at the gun input while it's running.
Here is an example:
Low flow 1/4" style coupler at the compressor connected to a 50 foot long 3/8" hose terminated at another M style coupler to the impact.
In order to obtain the guns rated torque at 90 PSI you need to overcome the system pressure drop which is likely to be 35-40 PSI per coupler plus 25-30 PSI for the hose plus the regulator droop. GOOD LUCK WITH THAT!

 

[bsaint]

But doesnt the flow through the gun drop the pressure across the orifice of the coupler? Its the same way we setup paint guns. 50 psi at the inlet for 20 psi at the nozzle. So if im loosing 17 pounds through my coupling at 4.8 cfm of my air tool, ill just crank that ***** up 17 pounds on the supply side.

Plus who runs at 90 psi anyways? Its just for a nominal rating. I run my guns at 30% higher pressure for theoretically 30% more force. Who knew snapon mg725 gun had 2000 ft pounds of nut busting torque lol

Cant do that with battery operated

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[sberry]

you are not using 4.8, you are using 20.

 

[bsaint]

you are not using 4.8, you are using 20.

When I increase pressure? It doesn't matter my compressor is 20hp.

 

[David C]

Your measurements are for static pressure and do not include velocity pressure. You need to measure total pressure after each coupler fitting. It is likely that the air flow is turbulent after each coupler so your test rig would need to be modified to get accurate values.

 

[DeeKay]

Your measurements are for static pressure and do not include velocity pressure. You need to measure total pressure after each coupler fitting. It is likely that the air flow is turbulent after each coupler so your test rig would need to be modified to get accurate values.

I agree, for repeatability sake. In industry we typically us at least ten pipe diameters of straight pipe without any fittings or obstruction upstream from the impulse tubing/transmitter or flowmeter and five pipe diameters of straight pipe downstream. Usually for pressure only measurements we don't worry about turbulence, but they are always a constant installation and a relative measurement. Since the couplers are changing the flow characteristics I guess it could change the pressure measurement a bit, I wonder how much though

 

[David C]

DeeKay,

Your pipe lengths after fittings is to insure fully developed flow provided that the Reynolds number indicates the flow in your piping is not turbulent.

Likely the reason you don’t measure velocity pressure is the velocity in your system is low and the velocity pressure insignificant.

Given the effort that stedlin put into his test makes it hard to say here that the test measurements do not have much meaning.

 

[Stedlin]

Your measurements are for static pressure and do not include velocity pressure. You need to measure total pressure after each coupler fitting. It is likely that the air flow is turbulent after each coupler so your test rig would need to be modified to get accurate values.

I realize that variations in turbulence will affect the result to a degree.
This was a spur of the moment endeavor. I've noticed that posts of this type generally don't get much notice so I tend to not put too much effort into them as a result.
If I can come up with some more piping and adapters I will repeat the tests.
However based on previous testing I don't expect a significant change in the results.
I appreciate your comments.

 

[DeeKay]

DeeKay,

Your pipe lengths after fittings is to insure fully developed flow provided that the Reynolds number indicates the flow in your piping is not turbulent.

Likely the reason you don’t measure velocity pressure is the velocity in your system is low and the velocity pressure insignificant.

Given the effort that stedlin put into his test makes it hard to say here that the test measurements do not have much meaning.

My guess is that it's not critical for our process followed by cost savings and packaging. Just curious, what would you consider low or high velocity? We flow 60,000 SCFH through a 4" pipe at my little N2 plant. How much of a difference is there between velocity pressure and static pressure? I love learning this kind of stuff.

 

[DeeKay]

I realize that variations in turbulence will affect the result to a degree.
This was a spur of the moment endeavor. I've noticed that posts of this type generally don't get much notice so I tend to not put too much effort into them as a result.
If I can come up with some more piping and adapters I will repeat the tests.
However based on previous testing I don't expect a significant change in the results.
I appreciate your comments.

Thanks for entertaining our questions/skepticism and not just saying "those are the numbers" like some companies. I might just have to try some of these out.

 

[David C]

DeeKay

Velocity pressure Pv =(rho)v*2/(2Gc)

Rho= fluid density
V=flow velocity
Gc=gravity constant in ft-lb-sec system Gc=32.2

What you might take from this is Pv is proportional to velocity squared. So for low velocities Vp is quite small and for higher velocities Vp can be quite significant.

It might be instructive to note that velocity pressure is what allows airplane wings to generate lift and why a higher airframe velocity generates more lift. Or in the case of racing cars with rear wings (that generate negative lift or downforce) not much benefit is achieved by speeds below 60mph. To head off any arguments about vehicle airfoils, lift is a function of airfoil design as well as velocity so downforce could be achieved at lower velocities with another wing profile, though at the penalty of high drag force at higher velocities.

When I mentioned high flow rates I was referring to high Reynolds numbers. High Reynolds numbers indicate turbulent flow and accurate measurements are not possible in a turbulent flow regime. I could give you the formula for Reynolds number calculation but it would take too much explaining.

In your case you do not mention the stagnation pressure in your 4” pipe system so calculation of the Reynolds number is not possible.

Understanding compressible fluid flow is complicated and application of a Reynolds number to any specific situation is not simple either. So a high Reynolds number in a pipe might be a low number in another configuration.

 

[Stedlin]

I repeated the original tests comparing pressure drop between two couplers with the same M style industrial plug. This time I separated the coupler under test from the pressure gauge to increase accuracy.

The difference in pressure drop @ 90 PSI is now 23 PSI.
If you use two of these with a hose which is common than double it to 46 PSI.
Add a 50 foot long 3/8" hose adds another 25 PSI drop and you'll need 161 PSI at the source just to get the rated torque from the impact gun.

 

[bsaint]

Damn crazy. Can you test Lincoln style?

 

[Stedlin]

Damn crazy. Can you test Lincoln style?

I could if I had some. My understanding is that they are the most flow restrictive on the market.

 

[Stedlin]

What I wrote earlier about the 161 PSI pressure requirement was incorrect.
Since the coupler/plug pressure drop is 38 PSI @ 90 PSI then I should have used 38 instead of 23.
38 * 2 (two couplers) = 76 + 25 PSI for the hose + 90 = 191 PSI.
Yikes!

It's not just a coupler, it's a flow restrictor!
Two for the price of one.

 

[Stedlin]

I attempted to achieve 90 PSI to the 1/2" impact using two M style couplers with a 50 foot long 3/8" hose. Almost made it with a whopping 90 PSI pressure drop.

 

[bsaint]

I could if I had some. My understanding is that they are the most flow restrictive on the market.

Hmm crazy. Thats what i use. Its my favorite. Quiet and easy to change. My gun never lacks power.

I think the restriction is in the coupling not the plug. But I dont know. Lincoln rates the coupler at 45 cfm @ 100 psi and rates the plug at 55 cfm @ 100 psi.

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[PT Doc]

Please test a Prevost Hi Flo

 

[Stedlin]

Hmm crazy. Thats what i use. Its my favorite. Quiet and easy to change. My gun never lacks power.

I think the restriction is in the coupling not the plug. But I dont know. Lincoln rates the coupler at 45 cfm @ 100 psi and rates the plug at 55 cfm @ 100 psi.

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CFM ratings without a pressure or pressure drop are meaningless AFAIC.

I did order one to test.

 

[Stedlin]

Please test a Prevost Hi Flo

No need to test it. The pressure drop is around 6 PSI or less per coupler at this pressure and flowrate.

My main point is that many who switched to HiFlo couplers probably didn't need to and could have gotten perfectly adequate performance by using better performing coupler bodies with the plugs they were already using.
In addition, HiFlo couplers all have issues working with other styles.

 

[Qualitytools]

No need to test it. The pressure drop is around 6 PSI or less per coupler at this pressure and flowrate.

My main point is that many who switched to HiFlo couplers probably didn't need to and could have gotten perfectly adequate performance by using better performing coupler bodies with the plugs they were already using.
In addition, HiFlo couplers all have issues working with other styles.

Thank You, very educational! I have the PREVOST and have been happy with their performance, so it's good to get confirmation

 

[Stedlin]

Thank You, very educational! I have the PREVOST and have been happy with their performance, so it's good to get confirmation

Prevost makes good couplers. No doubt about that. So do I.
Prevost safety couplers are a good choice for connecting a hose to the source.
I don't like them for connecting tools, especially air tools that don't retain pressure such as impacts, etc.

 

[sberry]

When I increase pressure? It doesn't matter my compressor is 20hp.

None of this would matter at 5 c.f. with these hose and fittings.

 

[AmericanMechanic]

Very interesting. It's always been annoying how weak air impact guns are. I thought it was (mostly) the crummy Chinese guns.

What you posted makes sense... i can fill a portable air tank to 90 and 120 PSI, but the flow rate (fill rate) gets increasingly slow as pressure climbs. (Which makes sijcegiven the pressure differential is less). Now I'm curious how much more torque I'd get with better air flow.

 

[Stedlin]

These highly flow restrictive 1/4" couplers are the same design that's been with us for over 70 years and they are still being mass produced.
We don't need HiFlo 1/4" couplers for use with 3/8" air hoses IMO.
Many people have switched to HiFLo European type couplers and had to switch out their plugs when they really didn't need to. Not only that, many attempt to use their standard plugs with the HiFLo couplers which don't work well.
They either leak or don't open the coupler all the way (don't open the valve completely) or both.

 

[bsaint]

CFM ratings without a pressure or pressure drop are meaningless AFAIC.

I did order one to test.

The pressures are right there. 100 psi


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[bsaint]

None of this would matter at 5 c.f. with these hose and fittings.

Then i have no idea how to understand what youre talking about. I understand pressure and flow. Ive engineered a lot of welding fixtures. I have orifice calculators that are pretty damn accurate and labview programs that accurately measure receiver pressures over time.

I get the manufacturer is trying to sell his couplings and what not but really he needs to have a 3rd party lab do testing. Its like having the dealer talk up his own car vs consumer reports reviewing the car.

Also he needs to put an impact gun on a force tester and I want to see his couplings drive the hammer harder inside the impact gun.


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