Psi and hose size question

[JorWood]

I was recently at my friend's shop and noticed he's running 1/4" connectors on all his tools - including his impact guns. When I asked him why he doesn't use 3/8" for his impacts he told me he doesn't need them because the shop runs at 150 psi.

My question is what air pressure do you have to have to equate to 90 psi with 3/8" connectors to make it the same with 1/4" connectors?

I like the idea of running the same size for all of my tools.

 

[pi_guy]

CFM is a bigger part of the equation.

 

[MEngineer]

There is a calculation that can be done if you provide the actual orifice diameters for the fittings that you are interesting in comparing.

 

[JorWood]

I thought 1/4" and 3/8" we're the relevant orifice sizes

 

[CrashmanS]

I run my body shop and always have with 3/8 air hose with standard 1/4 pipe thread air couplers. However the 1/4 pipe thread on the end of the hose is not 1/4 inside diameter. The hole might be 1/4 on the ****** part of the connector. I've ever had an issue of psi loss. They have high flow connectors for hvlp paint guns but I've never used them or noticed a difference. Now what you don't want to do is use 1/4 inch air hose for these applications. If you run big tools like 3/4 or 1 inch impacts, most people step up hose diameter to 1/2 or 3/4.

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[theoldwizard1]

The correct question to ask is "what is the PSI AT THE TOOL when it is in full operation.

Watch this video : Air Pressure : Working PSI - VS - Static PSI

 

[bigredmf]

I know a MAC dealer he was trying to track down a 1" gun as the 3/4" would not put out the torque the customer had hopped for.

Sold him a 3/4" air hose with 3/4" couplings and the customer was complaining it put out to much torque.

Though a 1/4" coupling may work on a impact you will get better performance with a larger coupling.

Also most air tools are rated and designed for 90 psi max.

Red

 

[woody6904]

I thought 1/4" and 3/8" we're the relevant orifice sizes

IMO, 1/4 and 3/8 relates more to thread size. Notice below both are 1/4 thread, but the "orifice" size is different.

http://www.garagejournal.com/forum/picture.php?albumid=2984&pictureid=31489

 

[sberry]

The connector isn't so much an issue as the hose size. !/4 is really small for i1/2 impacts, a heavy gun will draw down 40# loss over 50 ft of 3/8 and at least that over 25 of 1/4, maybe more. If the whips are short its less of a factor.

 

[bmwpowere36m3]

The hose will be the bigger restriction and pressure loss will depend on CFM... 3/8" couplers for most shop tools is overkill.

 

[astroracer]

pi_guy nailed it and everyone just kind of ignored him.
PSI is irrelevant if the fittings can't pass the CFM the tool needs. 1/4" fittings will flow less then 3/8th's. If an HVLP gun needs 70 cfm and the fittings only pass 50, the gun is not going to work correctly.
I run 1/2" hose and fittings for all of my automotive painting. Never have an issue with CFM or bumping up the PSI to compensate.
Going to bigger fittings and hose, especially over long runs, will increase the performance of any air tool plugged into the hose
Mark.

 

[woody6904]

1/4" fittings will flow less then 3/8th's.

Broad generalization that isn't always true. Compare a Milton 3/8 basic flow P style vs a Milton 1/4 basic flow V style.

Milton P = 68 CFM

Milton V = 74 CFM

 

[bmwpowere36m3]

Honestly all we've used is 1/4" coupler fittings (I/M) in the shop... 120 gal compressor, mostly 1-3/4" black pipe runs and then 1/2" drops or reels. HVLP guns, 1/2" impacts, blast cabinet, etc... never felt a "lack of performance".

 

[Danglerb]

CFM airflow is what matters, higher air flow means more pressure drop as the velocity of air goes up the pressure drop goes up by the square, double the velocity, four times the pressure drop (assuming I remember this from ages ago).

Higher pressure and smaller hoses and couplers seems like a dumb idea. Too much pressure on all the low crm tools and too little on the high cfm tools. OTOH a high flow 1/4 might be fine for most 1/2 impacts.

 

[woody6904]

Don't want to sound like an advertisement for Milton V style, but they are the best of both worlds IMO. Higher CFM with flexibility for large and small hoses. Can run a Milton V 1/4 thread on a 1/4 or 3/8 hose for normal stuff, and Milton V 3/8 thread on a 1/2 hose for more flow when needed.

 

[rhandwor]

You also need to have a large enough storage tank so your compressor can keep up with the demand.

 

[CrashmanS]

Honestly all we've used is 1/4" coupler fittings (I/M) in the shop... 120 gal compressor, mostly 1-3/4" black pipe runs and then 1/2" drops or reels. HVLP guns, 1/2" impacts, blast cabinet, etc... never felt a "lack of performance".

This.
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[Infinia]

My question is what air pressure do you have to have to equate to 90 psi with 3/8" connectors to make it the same with 1/4" connectors?
.

DEPENDS

I like to use a electric analogy I.E. Ohm's law
The compressor PSI output is the source voltage, The hose line PLUS any fittings represent Resistance or losses in pressure to the tool. The Actual CFM used is the current. CFM changes drawn by the tool/s and trigger position (this is the biggest variable).
The hose line at each diameter size has a loss per unit length, increase the length and the total resistance rises! Also the higher the CFM = more drop in pressure at the tool. Use a long hose then its losses dominate the losses due to fittings. etc. The fittings are a fixed loss and don't matter as much as widening the hose diameter and /or the total hose length. Increasing the compressor PSI can overcome pressure drops due to all the losses.

 

[Fish_Stick]

Don't want to sound like an advertisement for Milton V style, but they are the best of both worlds IMO. Higher CFM with flexibility for large and small hoses. Can run a Milton V 1/4 thread on a 1/4 or 3/8 hose for normal stuff, and Milton V 3/8 thread on a 1/2 hose for more flow when needed.

Just upgraded to the Milton V and had a very noticeable difference on an impact. Well worth the money.

 

[sberry]

DEPENDS

I like to use a electric analogy I.E. Ohm's law
The compressor PSI output is the source voltage, The hose line PLUS any fittings represent Resistance or losses in pressure to the tool. The Actual CFM used is the current. CFM changes drawn by the tool/s and trigger position (this is the biggest variable).
The hose line at each diameter size has a loss per unit length, increase the length and the total resistance rises! Also the higher the CFM = more drop in pressure at the tool. Use a long hose then its losses dominate the losses due to fittings. etc. The fittings are a fixed loss and don't matter as much as widening the hose diameter and /or the total hose length. Increasing the compressor PSI can overcome pressure drops due to all the losses.

This is really good.

 

[timothylockhart]

All I got from the real tool reviews video is that,

He recommended 1/2 hose

He used 1/4 fitting.

I need something to measure air pressure at tool (for load.)

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[JorWood]

I made a mistake in the title as the question was never regarding the hose size, I only use 3/8" hose. It should have said coupler size. The basic question is, using a 3/8" hose, how many PSI would I have to run with 1/4" connectors to generate the same CFM at the gun as running 90psi on a 3/8" connectors on a 3/8" hose? And we can assume it's just one 50' hose straight from the tank for the sake of argument.

Also having read all these posts it seems as though somehow different fittings flow more or less than others so this might be a moot point.

 

[Infinia]

Also having read all these posts it seems as though somehow different fittings flow more or less than others so this might be a moot point

It maybe less than 0-15 psi difference depending on actual CFM.
Every restriction in the line will drop some pressure across it. the only time it will flow less is when the supply psi can no longer support all the drops all along the hose to the tool.

The basic question is, using a 3/8" hose, how many PSI would I have to run with 1/4" connectors to generate the same CFM at the gun as running 90psi on a 3/8" connectors on a 3/8" hose?

What compressor PSI do you normally "run"? answering this question will test your air tool knowledge.

 

[JorWood]

Well I'm happy to admit that I am very new to all this. I just realized that I've been running my regulator wide open at 125 psi and have been trying to get my head around where it should be. Since my typical setup is about 150ft of line with 3 connectors and 2 air filters I'm starting to think 125 psi might not be over powering my small tools. And as far as I can tell running my impacts at 125psi on the 50' line shouldn't be to crazy for it.

 

[Infinia]

And as far as I can tell running my impacts at 125psi on the 50' line shouldn't be to crazy for it.

The pressure that really matters is measured at the tool when the trigger is opened, you will be lucky to see 90 psi w 50 ft of 3/8 at any range from 125-100 psi.


You will be mostly under powering the impact gun. The regulator pressure drops as the tank gets depleted. Note the pressure when the motor 'cuts in" this is when the impact is at its weakest, at this point you only have around 10 psi available to support all the drops from the long hose plus fittings (an almost impossible situation). Reducing hose length and any unnecessary quick disconnects will help. Consider adjusting the compressor pressure switch cut-in higher, this will give easiest rewards at the expense of higher duty cycles.
Best thing is experiment with a gauge at the tool. I would buy a hose remnant and shorten it to 15 ft for max punch. Sometimes the tank regulator is a restriction and some folks upgrade /bypass it! Of course if you had a 150 psi compressor it would be smooth sailing.

 

[sberry]

125 on 50ft of 3/8 is already underpowered for a real 1/2 gun and the connector doesn't mean very much.