Airbrushing

Model Railroader General Discussion (Model Railroader)
21

Hello All,

Rich, check your e-mail.

Sorry for the delay in responding.

Here’s my reply:

Hello Rich,

Sorry it’s taken me so long to reply.

Thank you for reaching out to me via e-mail.

I just looked at the Harbor Freight website and it appears that the exact regulator I have is no longer in stock.

This seems to be the one they now carry is:

https://www.harborfreight.com/air-tools-compressors/air-compressor-accessories/filters-regulators/150-psi-air-compressor-regulator-kit-with-dial-gauge-68223.html

It has Female 1/4 inch NTP fittings on each side.

What I did to plumb this was to remove the 1/4 inch NPT to 1/8 inch 27 NPT adapter (airbrush hose) on the stock moisture trap/pressure gauge.

I then used a Male/Male 1/4 inch NPT fitting to connect the regulator to the moisture trap. I found this in-store at Harbor Freight, but they are available and hardware and big box stores.

On the moisture trap side of the M/M fitting I added an “O” ring to prevent leaking.

Then on the regulator side of the M/M fitting I used Teflon tape on the threads to seal that side.

The stock 1/4 inch NPT to 1/8 inch 27 NPT fitting that I removed from the moisture trap threaded in to the other side of the regulator, again using Teflon tape to seal this side.

Without the “O” ring I did experience a leak. Adding this stopped the leak.

Let me know if you need more info.

Hope this helps.

22

JJ, thank you so much for getting back to me and for the detailed reply.

I never gave a thought to moving the compressor output fitting to the other side of the regulator. That was pure genius on your part. That’s the good news.

The bad news is that the fitting on my compressor is a 1/8" x1/8" fitting, not a 1/4" x 1/8" fitting. I do have a 1/8" x 1/8" fitting on hand, but I cannot thread it on the opening created on the compressor. So, I am right back where I started. Ugh.

The problem seems to come down to the threading. What is so baffling is that the air hose will connect the airbrush to the compressor, but the Central Pneumatic fittings seem incompatible with standard fittings.

The thing that is so weird about all of this is that the air hose supplied with the compressor fits both the airbrush input port (1/8"-27-NPS) and the compressor output port (1/8"-27-NPT). These are the stated fitting sizes in the owner’s manual.

Rich

23

Hello Rich,

Thank you for your kind words.

Which specific compressor are you dealing with (make and model)?

So if I’m understanding you correctly the output of your compressor body is 1/8 inch female?

On the regulator you are installing what size is/are the females?

Welcome to the nomenclature/nightmare of plumbing!

NPT refers to “National Pipe Taper” or the pitch of the threads.

Although the fittings are 1/8 inch on the airbrush hose, that pesky number “27” refers to the TPI- -threads per inch- -even though it is still an NPT fitting.

A “regular” 1/8 inch won’t mate with the 1/8 inch 27, NPT, as you have discovered.

“NPS”- -National Pipe Straight- -will mate with an NPT with the same TPI. In this case, they are both “27.”

There are a multitude of adapters that you can use to plumb the regulator inline eventually ending with a M 1/8 inch 27, NPT.

If you can answer the three questions I posed this will help us solve your plumbing dilemma.

Hope this helps.

24

Hi JJ,

The answers to your three questions are:

  1. The compressor is from Harbor Freight, Central Pneumatic No. 60328. It is a 1/5 HP 58 PSI Oil-Free Airbrush Compressor.

  2. The air outlet is 1/8" male. (More on this later)

  3. The air pressure regulator is also from Harbor Freight, Central Pneumatic No. 68223. It is a 150 PSI Air Compressor Regulator. Both sides of the regulator are 1/4"-18-NPT Female. I can confirm that those fittings sizes are accurate - - 1/4"-18-NPT Female.

The owner’s manual states that the air outlet on the compressor is 1/8"-27-NPT Male. It further states that the air inlet on the airbrush is 1/8"-27-NPS Male. That said, when I just went back to look at the compressor box, it states that the air outlet on the compressor is 1/8"-27-NPS Male. So, there is an inconsistency between the owner’s manual and the label on the compressor box that I just noticed for the first time.

My best guess is that the label on the box is correct. This would make sense since the air hose connects perfectly from the airbrush to the compressor. Therefore, the air hose fittings must both be 1/8"-27-NPS Female.

Interestingly, I do have NPT fittings where the 1/8"-27 female end connects to the 1/8"-27-NPS males. However, I have tried without success to connect a 1/8"-27-NPT male to a 1/8"-27-NPS female.

Rich

25

Hello Rich,

Thanks!

OK, that’s the exact same unit I have.

As I advised, remove the M/M fitting on the moisture trap- -the glass unit.

Don’t worry about the other dial gauge on the moisture trap- -leave it in place- -more on that later.

The 1/4 inch to 1/8 inch 27 NPS is what you will use to “adapt” from the newly installed regulator to the airbrush hose.

That F fitting from the moisture trap is where you will use the 1/4 inch M/M fitting to attach the pressure regulator with the “O” ring to prevent leaking.

The dial gauge on the moisture trap stays in place.

In the end, you will have both the pressure gauge on the moisture trap AND the pressure regulator.

I’m a “suspenders and belt” type of person so I also used Teflon tape on the threads of the fitting along with the “O” ring.

Apply Teflon tap to the other side of the M/M fitting.

Then thread on the pressure regulator.

On the output side of the pressure regulator apply Teflon tape to the M/M 1/4 inch NTP to 1/8 inch 27 fitting.

You have to remove the 1/4 inch NTP to 1/8 inch 27 NPS to plum between moisture trap to the pressure regulator.

In the end, you will have the dial gauge on the moisture trap along with the pressure regulator.

The pressure gauge on the moisture trap monitors the total output from the compressor.

By installing the pressure regulator you can control the pressure to the airbrush.

As you use the airbrush you will see a fluctuation in the pressure regulator gauge- -this is what you want.

Hope this helps.

26

If I understand correctly what you are suggesting, the problem is that the M/M fitting on the moisture trap on my unit is 1/8 x 1/8, not 1/4 x 1/8. I can post some photos to be certain that we are talking about the same fitting, but it is the air outlet on the compressor.

Rich

27

I took two photos of the compressor.

In this first photo, the M/M fitting is the silver colored one coming out of the upper portion of the moisture trap. It is 1/8" x 1/8". Is this the fitting that you are referring to?

In the second photo, this is a view from above.

28

Hello Rich,

YES!!!

Remove that fitting on the output side of the moisture trap!

On mine, it’s brass- -but no matter.

That’s where the M/M 1/4 inch fitting will go on the output of the moisture trap to the new pressure regulator.

Don’t forget the “O” ring to prevent leaking on the “upstream” (input) side of the pressure regulator.

Then attach the pressure regulator “inline” (output) from where you removed that fitting.

That same fitting will be the “output” of the pressure regulator so the airbrush hose will attach to that.

Leave the moisture trap and the regulator in place.

That should give you what you are seeking.

Hope this helps.

Post Script: Thank you for reaching out and never giving up on the solution you seek. HTH- -JJDI.

29

JJ, therein lies the problem. Your compressor air outlet port holds a 1/4 x 1/8 M/M fitting. My compressor air outlet port holds a 1/8 x 1/8 M/M fitting. So, I cannot do what you did. Interestingly, your fitting is brass. Mine is nickel plated brass for whatever that is worth.

Rich

30

I may have an explanation for why the M/M fittings are different on my and your compressor.

My compressor has an SKU 60328. However, the website shows three variations: 95630, 69434, and 60328. The link that you provided in an earlier reply shows SKU 95630. Check the actual number on your compressor if you get a chance.

Rich

31

Hello Rich,

The SKU on my unit is indeed 95630.

However, if you look under the specifications for all three SKUs it lists, “Thread Size- -1/8 in-27 NPT with 1/4 in-NPT adapter.”

Hope this helps.

32

Yes, I see that reference in the Specs. There is a similar reference in the Overview as well as on the compressor box which reads,

  • Direct hook-up with all airbrushes using 1/8 in-27 NPT with 1/4 in-NPT adapter

But, I honestly don’t know what that means. With the included hose, you can directly attach the airbrush to the compressor. No 1/4" adapter is needed.

When I first read how you replaced the air outlet fitting on the compressor, I removed the air outlet fitting on my compressor. It is 1/8"x1/8" M/M.

Rich

33

Hello All,

OK, Great!

That is the 1/8 inch NPT/NPS to 1/8 inch-27 NPT M/M adapter fitting that allows the airbrush hose to attach to the output of the moisture trap.

As I keep saying, remove the fitting on the output side of the moisture trap.

Put it aside because you will need it later.

No matter the size of the output of the moisture trap; 1/8 or 1/4 inch, the threads should be NPT.

That’s why the NTP to 27 NTP adapter fitting is used.

If the new air regulator is F/F 1/4 inch NPT on both the input and output sides, there is a reduction adapter that will go from 1/8 inch M NPT to 1/4 inch M NPT.

On the output side of the new regulator; 1/4 inch NPT, you will need a 1/4 inch M to 1/8 inch F NPT.

Then you can use the 1/8 inch NPT to 1/8 inch-27 NPT- -that you saved- -on the output of the newly installed regulator with the step-down 1/4 inch to 1/8 inch NPT adapter.

Your best option is to remove the current output fitting from the moisture trap, take the compressor and the new regulator to your local hardware/big box store, and “trial and error” the fittings you need.

In my experience with Ace Hardware stores, there is a section in the tool aisle that has air compressor-specific fittings.

The plumbing aisle has a more generic selection of fittings that offer a bigger selection, including step-up and step-down adapters.

You just need to find the correct fittings and adapters for your needs.

Hope this helps.

34

Just to make sure that we are speaking about the same fitting, is it the one circled in red?

It is a 1/8"-NPS Male x 1/8"-NPS Male fitting. The included air hose fits on this fitting. The included air hose will not fit on a 1/8"-NPT Male fitting.

Rich

35

This is an excerpt from one of my earlier replies. There is an obvious conflict in the various references to the size of the fitting.

Rich

36

Hello All,

Yes!

Remove that fitting you have circled.

That’s the adapter fitting you will need later, on the output side of the newly installed regulator to the airbrush hose.

The M/M fitting threads into where that fitting you circled was removed from on the moisture trap.

From there, it’s a matter of matching the output of the regulator to the fitting you first removed.

As I posted earlier, using an “O” ring between the moisture trap and the new regulator was needed to completely seal my system.

Hope this helps.

37

OK, I will try this in the morning and report back. However, I am doubtful that an NPT fitting will work in that opening. We shall see.

Rich

38

Hello All,

Have faith!

Hope this helps.

39

I tried my grand experiment this morning without success. I removed the 1/8"-27-NPS x 1/8"-27-NPS MxM fitting from the air outlet on the compressor and tried to replace it with a 1/8"-27-NPT x 1/8"-27-NPT MxM fitting. No dice. That did not surprise me. Although both NPT and NPS have the same thread angle, shape, and pitch (threads per inch), NPT threads are tapered and NPS threads are straight (parallel).

I think the fact that the Central Pneumatic compressor has three different SKUs on the Harbor Freight website indicates that the manufacturer has taken liberties with the compressor design, at least as it relates to the fittings.

If I am going to find a way to install an air pressure regulator on this compressor, I need a different solution.

Rich

40

Hello All,

You keep using the wrong fitting between the Female output of the moisture trap to the Female input of the pressure regulator you are trying to install.

The fitting you circled in your photo is not a 1/8"-27- x 1/8"-27 (dash twenty-seven designation)-NPS fitting as you keep erroneously presuming!

It is a 1/8 in-27 (dash twenty-seven designation) NPT on one end with either 1/8 in-NPT or 1/4 in- “standard” NPT on the other side, no “-27” (dash twenty-seven designation) on that end.

That’s why it is an adapter from “-27” (dash twenty-seven designation) threads to “standard” NPT threads!

One side of the M/M fitting is 1/8-“27” (dash twenty-seven designation) NPT to fit the airbrush hose.

The other side of the same fitting is a “standard” 1/8 inch NPT! (Or “standard” 1/4 inch NPT as on my unit.)

Note there is no “-27” (dash twenty-seven) thread designation on the opposite end of the fitting.

Trying to use a M/M fitting with the “-27” (dash twenty-seven designation) on both ends won’t fit the Female port on the moisture trap or the regulator whether it’s an NPT or NPS.

You need a M/M fitting with the “standard” NPT designation on both ends. Not a “-27” (dash twenty-seven designation) on either end!

PLEASE READ THIS VERY CAREFULLY:

Any fitting you use with a