testing done between 1/4 and 3/8 quick connect fittings?

[Kracin]

anyone ever seen or done any testing to see if the fitting size at the gun makes any significant difference in power?

brought my 3/4 cp-8272 to work and im wondering whether or not i should make a specific hose for it or not to avoid having air problems since 99.9% of the fittings on the plant air are 1/4 quick connects. not sure how much of the 1300ft/lbs of power i am going to end up losing if i keep it hooked up to the 1/4 fittings, all the air lines are 3/8, that go into the main air system at least.

 

[bcradio]

The 3/4" earthquake is less powerful than the 1/2" earthquake gun when both used with 1/4" fittings.

If using 3/8" fittings you'll want them all the way throughout the line, otherwise your one 1/4" fitting will be the bottleneck.

 

[Kracin]

The 3/4" earthquake is less powerful than the 1/2" earthquake gun when both used with 1/4" fittings.

If using 3/8" fittings you'll want them all the way throughout the line, otherwise your one 1/4" fitting will be the bottleneck.

thats comparing two items with significant difference in a cfm consumption scale though. 1/2 is rated at 6cfm avg, and the 3/4 is rated at 9cfm avg. thats 50% more air needed. and depending on who was using it they probably didn't have the capacity to support it. full load consumption of the cp 3/4 is 38 CFM. i doubt the HF lists what their full load consumption is either, and there aren't too many people who can support that much CFM consumption to take advantage of a LARGE impacts power. i have no doubts that whoever hooked up a large impact to a home compressor, had all kinds of trouble getting good power out of it. just my 2 cents on that at least.


i was hoping there would be somebody who had done some flow testing to check the actual air flow rates with different restrictions on the line.

 

[Kracin]

ok well i was doing some more research, and milton's website has a chart for flow. which is pretty interesting actually.

they list their 1/4 fittings at a minimum of 32CFM flow, and their largest 1/4" fitting (the V that everybody likes) is listed at 74 CFM

now, considering that the air consumption at load of some tools. my 734h , a 1/2" impact only consumes 15 cfm at load. which is no problem. and the 3/4 i'm trying to determine sizing for consumes 36 cfm at load. just from a guess i'd think that there should be little to no issue running the impact on plant air with normal 1/4 fittings.

although i wonder where people are getting their info that they need those V style fittings with almost twice the flow to properly run some of their air tools when they should be maxed out already on the tool? is there something i'm missing here?

 

[Scimmia]

Yes, you're missing pressure drop. Those flow numbers are at some arbitrary "acceptable" pressure drop, which might not be so acceptable to you or me.

 

[Kracin]

Yes, you're missing pressure drop. Those flow numbers are at some arbitrary "acceptable" pressure drop, which might not be so acceptable to you or me.

pressure drop more relates to hose size and length of hose. not the single fitting on the end. (unless you start adding in tons of elbows and lengths of pipe to cause extra restrictions.

i think the last post in this thread points it out better than it has been said so far

http://www.garagejournal.com/forum/showthread.php?t=18354

basically, the air in the hose is at a specific cfm by the time it reaches that fitting, and at a specific pressure. provided the fitting isn't incredibly small to the point of creating a huge restriction, the air coming out of the fitting will have the same CFM as in the hose but at a higher pressure. same amount of air but higher pressure due to the force of it being pushed out, i'm sure with enough of an orifice size drop you could get a significant drop in cfm coming out. but i doubt every single Quick disconnect maker got their charts wrong with the maximum allowable CFM @ standard pressures.

 

[wild cowboy]

basically, the air in the hose is at a specific cfm by the time it reaches that fitting, and at a specific pressure. provided the fitting isn't incredibly small to the point of creating a huge restriction, the air coming out of the fitting will have the same CFM as in the hose but at a higher pressure. same amount of air but higher pressure due to the force of it being pushed out, i'm sure with enough of an orifice size drop you could get a significant drop in cfm coming out. but i doubt every single Quick disconnect maker got their charts wrong with the maximum allowable CFM @ standard pressures.

No.

In fluid dynamics, a fluid's velocity must increase as it passes through a constriction, while its static pressure must decrease in accord with the principle of conservation of mechanical energy.

This is called the venturi effect.

This pressure drop, due to Bernoulli's principle, is the basic principle on how your car's A/C system works, the restriction there being the orifice tube or else the expansion valve. This sudden drop in pressure (from the restriction) is what creates the cold.

Another example of the venturi effect in action is, ever notice the more you use an air tool the colder it gets? - and you would think that using it hard would make it run hot!

It's weird to think about, but when you cover the end of the water hose with your thumb "to get higher pressure" when hosing off your sidewalk, you are actually getting lower pressure! (but higher speed)

for our purposes here, compressed air can be considered a fluid

 

[bcradio]

thats comparing two items with significant difference in a cfm consumption scale though. 1/2 is rated at 6cfm avg, and the 3/4 is rated at 9cfm avg. thats 50% more air needed. and depending on who was using it they probably didn't have the capacity to support it. full load consumption of the cp 3/4 is 38 CFM. i doubt the HF lists what their full load consumption is either, and there aren't too many people who can support that much CFM consumption to take advantage of a LARGE impacts power. i have no doubts that whoever hooked up a large impact to a home compressor, had all kinds of trouble getting good power out of it. just my 2 cents on that at least.


i was hoping there would be somebody who had done some flow testing to check the actual air flow rates with different restrictions on the line.

I think some compressor 101 training is needed for you before we continue.

 

[Kracin]

I think some compressor 101 training is needed for you before we continue. [emoji106]

Why not explain then, been waiting for somebody to chime in for a while, but with something useful

 

[Scimmia]

pressure drop more relates to hose size and length of hose. not the single fitting on the end. (unless you start adding in tons of elbows and lengths of pipe to cause extra restrictions.

i think the last post in this thread points it out better than it has been said so far

http://www.garagejournal.com/forum/showthread.php?t=18354

basically, the air in the hose is at a specific cfm by the time it reaches that fitting, and at a specific pressure. provided the fitting isn't incredibly small to the point of creating a huge restriction, the air coming out of the fitting will have the same CFM as in the hose but at a higher pressure. same amount of air but higher pressure due to the force of it being pushed out, i'm sure with enough of an orifice size drop you could get a significant drop in cfm coming out. but i doubt every single Quick disconnect maker got their charts wrong with the maximum allowable CFM @ standard pressures.

********. Some people try to overthink this, but it doesn't work that way. Yes, long runs of hose will drop pressure, but a single restriction will as well. Just kink your air hose and see what happens. There's very little length there, but it still drops pressure like crazy.

 

[Kracin]

The question im posing that seems to elude most people is that if a standard 1/4 fitting is rated for a max cfm of 36, why is every worried about putting one that flows 74 on a hose that creates more restriction than the fitting. But still flows enough to run any 1/2 impact at max power no problem

 

[Scimmia]

The question im posing that seems to elude most people is that if a standard 1/4 fitting is rated for a max cfm of 36, why is every worried about putting one that flows 74 on a hose that creates more restriction than the fitting. But still flows enough to run any 1/2 impact at max power no problem

You're making a whole lot of assumptions there. What does "rated for" mean? Does the .375" ID hose create more restriction than the .18" ID fitting? Does it flow enough to run that 1/2" impact at max power?

 

[Kracin]

You're making a whole lot of assumptions there. What does "rated for" mean? Does the .375" ID hose create more restriction than the .18" ID fitting? Does it flow enough to run that 1/2" impact at max power?

i already stated early on that it's being used in a plant. i'm using less than 10' of hose from a main plant air source that is at a constant 110psi, or 90 working from 1/2" pipe ran from 1" pipe that meets the 6" main. i shouldn't at all need to bother with thinking hose diameter is going to play any role with such a short length using 3/8, when sub 10' 3/8 hose has very little pressure drop with less than 40 cfm.

unless somebody wants to correct me on this.

i'm purely talking about the one "restriction" caused by a 1/4 QD fitting going into a tool that requires right about 36 max air consumption cfm, which is what a standard 1/4 is supposed to flow at max

 

[Kracin]

No.

In fluid dynamics, a fluid's velocity must increase as it passes through a constriction, while its static pressure must decrease in accord with the principle of conservation of mechanical energy.

This is called the venturi effect.

This pressure drop, is the basic principle on how your car's A/C system works, the restriction there being the orifice tube or else the expansion valve. This sudden drop in pressure (from the restriction) is what creates the cold.

Another example of the venturi effect in action is, ever notice the more you use an air tool the colder it gets? - and you would think that using it hard would make it run hot!

It's weird to think about, but when you cover the end of the water hose with your thumb "to get higher pressure" when hosing off your sidewalk, you are actually getting lower pressure! (but higher speed)

for our purposes here, compressed air can be considered a fluid

you seem to understand principles of it. and yes i did misspeak because there has to be something getting lower in order to have something else get higher, ie, can't have a higher pressure and the same flow rate without an increase somewhere else.

but how do you apply this to an air system? analogies don't really help me in this case.

in the case of an air system, having a higher pressure before the tool would solve the issue of having the loss in flowrate at the other side with the increased pressure right? so how much extra pressure are you thinking a system needs at the hose before the fitting, to make up for the drop in flowrate/cfm to run a tool that requires the maximum amount of flow a fitting allows through? or does it need any extra at all considering you may already be sized correctly?

i've been looking and it looks like everybody has a lot of ideas on it but no one has really done any testing that i can see. anybody have any links?

 

[Scimmia]

i already stated early on that it's being used in a plant. i'm using less than 10' of hose from a main plant air source that is at a constant 110psi, or 90 working from 1/2" pipe ran from 1" pipe that meets the 6" main. i shouldn't at all need to bother with thinking hose diameter is going to play any role with such a short length using 3/8, when sub 10' 3/8 hose has very little pressure drop with less than 40 cfm.

I was responding directly to where you said:

why is every worried about putting one that flows 74 on a hose that creates more restriction than the fitting.

i'm purely talking about the one "restriction" caused by a 1/4 QD fitting going into a tool that requires right about 36 max air consumption cfm, which is what a standard 1/4 is supposed to flow at max

Again, you're talking about "supposed to flow at". What does that mean? 30PSI drop at that flow? 40? 50?

 

[Kracin]

I was responding directly to where you said:




Again, you're talking about "supposed to flow at". What does that mean? 30PSI drop at that flow? 40? 50?

the pressure drop using calculators using 100 psi at 36 cfm through a 1/4 fitting shows 4-5 psi. the pressure drop using charts with 3/8th hose at 50 ft shows about 13 psi.....

so aside from all the guesswork, elminiate the hose altogether from your thinking, the hose isn't a worry like i said earlier. i'm talking purely fittings.
using the given diameter of the standard fitting, and the length of that section of the fitting, i'm getting negligible amounts of pressure drop through the fitting at the given cfm. so where is everybody getting all their information if this still seems to be an issue for people?

all i'm trying to find out is how much you can expect to flow at a maximum through a standard 1/4 quick disconnect to run larger tools, and at what point you 'need' to run larger fittings, not when you 'might want to' run larger fittings.

 

[blacK20]

Not sure what field you work in, but I'm in automotive/light truck and this is what I do. Use a 3/8" coupler right off the wall piping. I have a 1/2" air hose with 3/8" couplers/fittings specifically to use with the 3/4" gun when the time calls for it. My regular hose is 3/8" with 1/4" coupler on the tool end, BUT 3/8" fitting with 1/4"NPT threads on the wall end. Now when I need 3/4" gun power, all I have to do is swap air hoses at the wall coupler and the gun will have sufficient air volume to produce the needed power.

 

[Kracin]

Not sure what field you work in, but I'm in automotive/light truck and this is what I do. Use a 3/8" coupler right off the wall piping. I have a 1/2" air hose with 3/8" couplers/fittings specifically to use with the 3/4" gun when the time calls for it. My regular hose is 3/8" with 1/4" coupler on the tool end, BUT 3/8" fitting with 1/4"NPT threads on the wall end. Now when I need 3/4" gun power, all I have to do is swap air hoses at the wall coupler and the gun will have sufficient air volume to produce the needed power.

so you are swapping the hoses via a quick disconnect at the wall? both hoses have the same fitting, so i'm assuming you use a 3/8ths QD at the wall and put one on both hoses?

i would do the same thing and call it a day, but most of the air drops you find where i work are plumbed from 1/2" pipe and already have 1/4 QD on the ends, 3/8ths is rare to find just sitting there, and its not convenient to just throw a 3/8ths on the pipe when you need it because sometimes the smart guys before you put the only isolation valve in the ceiling 30 foot up.

 

[blacK20]

so you are swapping the hoses via a quick disconnect at the wall? both hoses have the same fitting, so i'm assuming you use a 3/8ths QD at the wall and put one on both hoses?

i would do the same thing and call it a day, but most of the air drops you find where i work are plumbed from 1/2" pipe and already have 1/4 QD on the ends, 3/8ths is rare to find just sitting there, and its not convenient to just throw a 3/8ths on the pipe when you need it because sometimes the smart guys before you put the only isolation valve in the ceiling 30 foot up.

Ya that's pretty much it. The 1/2" pipe off the wall originally had a 3/8-1/4"npt reducer and 1/4" coupler but nobody stopped me from removing the reducer and swapping in a 3/8" coupler for my own work bay. I'm using Milton typeV to be exact which comes in both 1/4" and 3/8"NPT making it very easy. After that it was a matter of swapping air hoses and voila.

Ya I know what you mean by the shutoff valve being in a retarded spot. I'm always the first person in the shop. So one morning I went to flip off the compressor, drained the air out, did my little monkey business, and flipped the compressor back on Nobody ever knew what happen.

 

[Kracin]

Ya that's pretty much it. The 1/2" pipe off the wall originally had a 3/8-1/4"npt reducer and 1/4" coupler but nobody stopped me from removing the reducer and swapping in a 3/8" coupler for my own work bay. I'm using Milton typeV to be exact which comes in both 1/4" and 3/8"NPT making it very easy. After that it was a matter of swapping air hoses and voila.

Ya I know what you mean by the shutoff valve being in a retarded spot. I'm always the first person in the shop. So one morning I went to flip off the compressor, drained the air out, did my little monkey business, and flipped the compressor back on Nobody ever knew what happen.

hah, just wait til somebody goes to use the air line and has a "wtf" moment...

 

[blacK20]

hah, just wait til somebody goes to use the air line and has a "wtf" moment...

Naw that won't happen. The coupler on the tool end of the 3/8" air hose is still the milton L shaped that is used throughout the shop. The only case that can set a moment of confusion for somebody else is if I left my 1/2" hose plugged in which is a V coupler/fitting on both ends of the hose. Or maybe if the hose blows out and somebody goes to swap in another hose that is pre fitted. I work there 99% of the time so I'm gonna set things up my way. Life is too short to worry about the 1 day out of the year.

 

[dnschmidt]

With HVLP spray guns the difference between Milton M and Milton V is dramatic. My SATA Nr2000 sprays way better with the V fittings. These things are air hogs consuming 18cfm when wide open and I can tell you that even when using a regulator at the inlet of the spray gun, which I always do, specifically one made by Reading Technologies the MR-1, the V fittings spray much better. You can actually see it in the width of the fan. These things run at 29PSIG with the trigger pulled so perhaps the difference is much more noticeable at this relatively low pressure but believe me it is VERY noticeable.