Air compressor pipe sizes

1. Air Compressor performance issue in regards to HVLP spraying. Air compressor outlets are 1" NPT. First filter is 4in diameter, 12in long, with 1" ports. Then other elements further down stream are all 1/2" NPT.

Question: Reducing the tank and first filter to 1/2" NPT and use a 1/2" ball valve between them?
Or using 1" pipe from tank to 1" ball valve. And 1" pipe to first filter, and adjust to 1/2" NPT further downstream. So, is a wider input port on the first filter going to change the coalescing performance. The 1" pipe will be stronger in regards to a given run length and will take more force to rupture it at the tank connection.

2. I'm also using Hoke Gyrolok tube fittings.

Question: Should a thin wall tube (like 5/8 OD which would be used with Hoke 1/2" tube fittings) be trusted to hold the full tank pressure? That would be the run from the tank to the ball valve. Or should thicker pipe and fittings be used from tank to ball valve?

3. Air leakage.

A slow reduction in PSI over a week. Eventually the compressor cycles a few times a year. I think the Hoke fittings will seal better than taped threads.

1" is better than 1/2", if you need it. How big is your compressor? How much air are you using and how long is the run?

I have 1/2" everything from the tank to my biggest air hog, about 25' run and 12 cfm. I lose about 15 psi so I have to set the shop regulator higher to compensate, mill has it's own regulator. Shop regulator is 12' from the mill.

Threaded fittings work just fine if you make sure they are sealed.

Mine is same as DavidScott: 1/2" pipe, I used soldered copper, and multiple regulators where needed.

My compressor is small and I don't really use it much, so my setup is adequate.

LM

Cut out the guesswork, that info had been around for eons.

Use this Compressed Air Pipe Line Capacity and the other calculators listed below.

IME, one of the most important things to check out is the flow rate through various valves and filters, PR sets and regulators etc etc etc etc.

DavidScott said:

I have 1/2" everything from the tank to my biggest air hog, about 25' run and 12 cfm. I lose about 15 psi so I have to set the shop regulator higher to compensate, mill has it's own regulator. Shop regulator is 12' from the mill..

Click to expand...

Question here... Is this a good place to put an accumulator tank? To try and avoid the
pressure drop?? Then you can run your compressor at a lower pressure and save some $$ in
electricity. I saved on average a bit over $100 a month by cycling 90ish to 120ish instead
of 115-145 or so.


As for pipes being able to hold the air pressure... Or the connections.. If you are
running normal pressures.. 100 to maybe 150 psi, you could probably get away with a
garden hose if you had to.. That's the last thing I would worry about.

Bobw said:

Question here... Is this a good place to put an accumulator tank? To try and avoid the
pressure drop?? Then you can run your compressor at a lower pressure and save some $$ in
electricity. I saved on average a bit over $100 a month by cycling 90ish to 120ish instead
of 115-145 or so.


As for pipes being able to hold the air pressure... Or the connections.. If you are
running normal pressures.. 100 to maybe 150 psi, you could probably get away with a
garden hose if you had to.. That's the last thing I would worry about.

Click to expand...

My mills want 60 psi so I am already cycling 80-120. Since the run is only 25 feet I think my problem is plumbing. I am pretty confident that 1/2" is just too small for my needs.

You don't mention pressure or the CFM you require, so it's tough to guess those missing variables.
Typical air flow (at 100PSI) thru 1/2" pipe is about 55CFM, and 1" pipe flows 150CFM.
How much air flow (CFM) do you need for your HVLP spraying operation??

If your compressor is cycling a COUPLE TIMES A YEAR due to leaks, you have far fewer air system problems than most other shops out there.
I've been in some medium size shops with 50 Horsepower installed.
30-40 goes to service, and 10-20 goes to servicing leaks.

rons said:

1. Air Compressor performance issue in regards to HVLP spraying. Air compressor outlets are 1" NPT. First filter is 4in diameter, 12in long, with 1" ports. Then other elements further down stream are all 1/2" NPT.

Question: Reducing the tank and first filter to 1/2" NPT and use a 1/2" ball valve between them?
Or using 1" pipe from tank to 1" ball valve. And 1" pipe to first filter, and adjust to 1/2" NPT further downstream. So, is a wider input port on the first filter going to change the coalescing performance. The 1" pipe will be stronger in regards to a given run length and will take more force to rupture it at the tank connection.

2. I'm also using Hoke Gyrolok tube fittings.

Question: Should a thin wall tube (like 5/8 OD which would be used with Hoke 1/2" tube fittings) be trusted to hold the full tank pressure? That would be the run from the tank to the ball valve. Or should thicker pipe and fittings be used from tank to ball valve?

3. Air leakage.

A slow reduction in PSI over a week. Eventually the compressor cycles a few times a year. I think the Hoke fittings will seal better than taped threads.

Click to expand...

DavidScott said:

1" is better than 1/2", if you need it. How big is your compressor? How much air are you using and how long is the run?

Click to expand...

5hp. 10.5 to 14 CFM depending on air cap. Gun pressure is 29 PSI, which is not a problem. CFM probably is not a problem, just want all I can get into the system.

Check your filters valves and regulators.

Watch the GUNMAN on youtube, no one sets spray gun pressure on the wall, you always set it on the gun flowing to allow for all those bends, restrictions and couplings, i like a air line reg set at about 35-40psi then dial down at the gun. Constant on the gun pressure is not just about the best pressure to spray at, its about maintaining a constant level of finish.

10CFM at 100psi is very diffrent to 15cfm at the sub 30PSI a typical HVLP takes. Roughly speaking ignoring temperature effects every time you half the pressure you double the volume, so drop a 100psi at 15CFm to 50 psi and you get 30CFM of air.

I have a lowly but very real and very constant 8cfm of compressor at 148PSI (HVO2 hydrovane) with a 75 litre tank it has no issues at all with keeping a tank full of air with even a 2mm HVLP setup spraying textured coatings at 30 PSI at the gun (U pol Raptor) hell i blast with a pressure pot and it will just about keep a 3mm nozzle a nats over 90PSI.

Charge the compressor and its hot, pressure will often drop a little if it sits there as the tank of air cools and shrinks. If after a couple of hours it still drops you got a leak. Either from pipe work or through the pump check valve or auto drain running. When i use air i tend to really use it, then often it will sit for weeks unused. Yeah i drain the water but why vent good compressed air? If there’s no leaks the pressure does not drop and no leaks is just as achievable with threads as it is with any of the fancy fittings. Any one tells you other wise there lying.

The advantage of large pipe is more storage, less restriction and slower flow, which helps moisture drop out. But a spray gun or a blow gun or even most of the smaller air tools will be happy on less than 50' of 1/2" or even 3/8". Now get into the bigger air impact wrenches and large air tools and yeah it matters, but its just like electrical cable sizing it comes a point were bigger gains you little and very much becomes a pain in the ass to manipulate. Drag a 1/2" hose on a gun for long and you soon see the benefit of a smaller higher pressure line with a on the gun regulator!

Tagging along on this thread I have always wondered if it is good practice to use a larger filter on a line. For example on a 1/2 line I might install a one inch npt filter because I have one sitting around. Will the bigger filter allow less restriction and more air flow or.. .will it be too big and not swirl the air around to effectively remove moisture and suchlike bad stuff in the air stream.
In case you can't tell I do not understand how a filter works beyond the hole size in the filter media. But there might be some cyclonic action involved I think.
Bill D.

Some of the chinese knock of air filter regulators are bloody good, i got turned onto them from a customers on site engineer, build quality not far off name brand and really solid products, theres no point paying a name brand fortune for em thats for sure any more!

Limy Sami said:

Cut out the guesswork, that info had been around for eons.

Use this Compressed Air Pipe Line Capacity and the other calculators listed below.

IME, one of the most important things to check out is the flow rate through various valves and filters, PR sets and regulators etc etc etc etc.

Click to expand...

I use this air CFM gauge. At the very top is the 1/4 NPS fitting on a paint gun. I use a custom fitting I made with only a gauge to measure the pressure at the inlet to the gun. I do not use the standard regulator/gauge contraptions any more. I have measured a 12% drop in CFM with those regulator/gauge combos on 3 different gun models.

Notice that I stepped down the ports on the gauge to 1/4". Would that alter the calibration of the air gauge? So I asked King technical support and they told me that it does not matter.



The custom stainless fitting with gauge attached to a Sagola 4500 Xtreme.

any drop in CFM is down to flow rate, .....which can only be down to pipe size, ....at a given pressure, any orifice or tube / pipe / hose can only pass so much air, and the lower the pressure, the more susceptible it is to hole size.

That said, despite their nominal sizes some fittings are shall we say ''very fleet'' on bore diameter, with nipples being a prime example, ......just for the hell of it, remove the nipples on that flow meter and see if there's any metal that can safely be drilled out ...a ''10 minute job'' .......hose unions are another problem area.

And you could try removing the hose -plumb the gun straight in to the flow meter etc etc, FYI (just in case ) hoses can collapse / or break up inside causing problems.

rons said:

I do not use the standard regulator/gauge contraptions any more. I have measured a 12% drop in CFM with those regulator/gauge combos on 3 different gun models.

Click to expand...

Just my 2CW, but Limi's advice and linked resources were worth saving.

Meanwhile.. that 12%? Before I would look to "custom" anything, filters most of all, I'd ask if simply paralleling two of 'em or going to a larger one might be better value for time and money?

Same again with Ells and such. Fewer bends, smoother bends if you have to fab sumthin', or even two 45 degree store-bought's adjacent will flow better than a mess of more turbulent 90-degree Ell's and Tees.

Similar Physics at work as a long-sweep Ell on a sanitary waste line vs a "close" Ell for a vent. Or the intake & exhaust on an IC engine. Torturing or restricting any "fluid" flow means parasitical losses go up.

I do not use the standard regulator/gauge contraptions any more.

Do you mean to say that you do regulate the air flow to the gun? Many guns have a top pressure of around 50psi so 120 psi shop air may cause them to explode in your hands and face. I do not understand how you regulate the flow and pressure to the gun with your setup.
harbor freight sells a "pressure regulator" which is just a needle valve and a pressure guage. It does work for a constant on load that is less then the compressor can supply. not good for my nailguns.
Bill D

rons said:

5hp. 10.5 to 14 CFM depending on air cap. Gun pressure is 29 PSI, which is not a problem. CFM probably is not a problem, just want all I can get into the system.

Click to expand...

This is one of the more confusing threads I've read. 10.5 to 14 CFM depending on WHAT? Normally that would be pressure... likely 14CFM calculated displacement, but 10.5 CFM at some reasonable pressure.

The HV in HVLP is high volume. I'm sorry, but most HVLP guns I've seen are rated to use way over 10CFM, one of the reasons I don't use them.

Flow through different sizes of pipe can be found from numerous charts found on the web.

Likewise, regulators are rated in CFM of flow also. If yours isn't, buy one that is.

Small openings in hose fittings, etc. are only a problem if the air supply is sized exactly to the gun. Try sizing everything 150%-200% of the gun's rated flow, and things will be fine.

Dennis

Limy Sami said:

any drop in CFM is down to flow rate, .....which can only be down to pipe size, ....at a given pressure, any orifice or tube / pipe / hose can only pass so much air, and the lower the pressure, the more susceptible it is to hole size.

That said, despite their nominal sizes some fittings are shall we say ''very fleet'' on bore diameter, with nipples being a prime example, ......just for the hell of it, remove the nipples on that flow meter and see if there's any metal that can safely be drilled out ...a ''10 minute job'' .......hose unions are another problem area.

And you could try removing the hose -plumb the gun straight in to the flow meter etc etc, FYI (just in case ) hoses can collapse / or break up inside causing problems.

Click to expand...

As the diameter of the air passage decreases the velocity increases at the same pressure.

I have seen and owned fittings of the same outside dimensions but the internal passages being wide and narrow. For example, a 1/4 NPT male-to-male with a narrow passage can be turned down to 1/8 NPT on one side.

Modelman said:

This is one of the more confusing threads I've read. 10.5 to 14 CFM depending on WHAT? Normally that would be pressure... likely 14CFM calculated displacement, but 10.5 CFM at some reasonable pressure.

The HV in HVLP is high volume. I'm sorry, but most HVLP guns I've seen are rated to use way over 10CFM, one of the reasons I don't use them.

Flow through different sizes of pipe can be found from numerous charts found on the web.

Likewise, regulators are rated in CFM of flow also. If yours isn't, buy one that is.

Small openings in hose fittings, etc. are only a problem if the air supply is sized exactly to the gun. Try sizing everything 150%-200% of the gun's rated flow, and things will be fine.

Dennis

Click to expand...

Look at the different air caps for a particular HVLP gun. The WHAT is the changing of a air cap. All with the gun handle pressure at the same pressure, usually 29 PSI.

Bill D said:

I do not use the standard regulator/gauge contraptions any more.

Do you mean to say that you do regulate the air flow to the gun? Many guns have a top pressure of around 50psi so 120 psi shop air may cause them to explode in your hands and face. I do not understand how you regulate the flow and pressure to the gun with your setup.
harbor freight sells a "pressure regulator" which is just a needle valve and a pressure guage. It does work for a constant on load that is less then the compressor can supply. not good for my nailguns.
Bill D

Click to expand...

If you look at the picture of my paint gun handle fitting, it has a gauge the is set for 29 PSI. Naturally a 25 or 50 foot air line from the regulator means that the pressure at the regulator is higher than 29 PSI.

Sata rates the combo regulator/gauge contraption (or cheater valve with gauge) as the 3rd choice.
A straight through fitting with only a gauge is the 2nd choice.
A digital display paint gun is the 1st choice.