A siphon feed airbrush has the paint holder hanging below the airbrush and relies entirely on air pressure to pull the paint out of the holder, and a gravity feed has the paint holder on top of the airbrush and uses a combination of gravity and air pressure to draw the paint from the holder into the mixing area.
What these two names are essentially describing, siphon feed and gravity feed, is the method of getting the paint from the paint holder, or cup, to the area of the airbrush where the paint mixes with the air and atomises.
Both types of airbrush are common in modeling fields although there might be a slight preference towards gravity feeds for higher end detail work.
This probably sounds great to hear but let’s look at them both in detail to get a better understanding of what the terms siphon feed and gravity feed actually mean in practise.
How Does A Siphon Feed Airbrush Work
A siphon feed airbrush works by creating a low pressure environment with compressed air to draw paint out of a paint bottle attached to the bottom of the airbrush, where it is then atomised and sprayed in a specific spray pattern onto your work.
The bottle attached to the airbrush has a paint tube installed in it with one end at the bottom of the bottle to draw up the paint, and the other end positioned in the airflow passing through your airbrush when the trigger is pressed.
The airflow passing through the airbrush causes a low pressure environment at the top end of the paint tube which causes the paint to be sucked out of the paint bottle, and it is then mixed with the air to atomise.
The paint bottle may come in various different sizes and can be removed for cleaning, with the benefit of being able to have multiple paint bottles with different colour paints in them able to be swapped in and out very quickly, sometimes with minimal clean up other than for the paint tube.
Which importantly brings us to internal and external mix siphon feed airbrushes…
Internal Mix Vs External Mix On A Siphon Feed Airbrush
An internal mix airbrush is an airbrush that mixes the paint with the air flow inside the body of the airbrush in what is called an atomisation chamber, where the paint is atomised and sprayed onto your work.
An external mix airbrush in one where the paint and airflow are mixed outside of the airbrush body itself and can give a slightly different spray pattern, being more of a ‘D’ shape rather than a cone.
Siphon feed airbrushes come in both mix types, and you can easily tell which type a given airbrush is.
If it has the paint tube going directly from the bottle into the body of the airbrush it is internal mix, and if the paint tube goes to a nozzle that you can see ends externally at the forward end of the airbrush (where it will meet the airflow) it is external mix.
It’s widely reported that internal mix tends to give a better spray pattern but there are many extremely capable external mix airbrushes available that will give you very good results on your scale model paintwork and they shouldn’t be overlooked.
Advantages of a Siphon Feed Airbrush
- Easy to quickly change bottles with different colours in them;
- Bottle sizes can be changed to accommodate different volumes of paint;
- Often less expensive than gravity feed airbrushes;
How Does A Gravity Feed Airbrush Work
A gravity feed airbrush is one that has a paint cup attached to the top of the airbrush allowing gravity to pull the paint down into the airstream inside the airbrush body and tip, where it then flows into a mix chamber to be atomised and formed into a cone shaped spray pattern.
Gravity feed airbrushes typically require less pressure to get the paint to flow that siphon feed airbrushes due to gravity helping the process.
For this reason gravity feed airbrushes with their low pressure capabilities are often preferred for fine lines and detail work.
It’s true that gravity feed airbrushes can come with exceptionally small nozzle and needle sizes although any benefit of a nozzle and needle combination smaller than around 0.2 mm is lost on scale models.
The lower pressure capabilities of a gravity feed airbrush may, however, be beneficial in being able to spray smaller parts without blowing them away… an problem almost every modeler bangs their head on the wall with from time to time. 😬
Paint wastage also becomes less of a problem with gravity feed airbrushes.
Siphon feed airbrushes require a minimum air pressure to suck the paint out of the paint bottle, whereas the gravity feed system literally has gravity assist greatly in pulling the paint into the airflow allowing for a lower pressure.
This means that you will get less overspray with the lower pressure gravity feed airbrush as it doesn’t need to push the paint out as fast as the siphon feed airbrush all other things being equal.
Additionally, you will often find with a siphon feed airbrush that there’s a certain amount of paint in the bottom of the paint bottle that can’t be sucked out at any level of pressure, a problem the gravity feed airbrush simply doesn’t have.
For this reason there is less paint wastage given that all of the paint in the gravity feed paint cup can be used.
Internal Mix Vs External Mix On A Gravity Feed Airbrush
If there’s an external mix gravity feed airbrush on the planet I’ve never seen it.
There’s no comparison of any benefits of one over the other here as you’ll likely never see an external mix gravity feed airbrush.
Advantages of a Gravity Feed Airbrush
- Requires less pressure all other things being equal, therefore it’s possible to get better detail work and experience less overspray and wastage;
- Requires less paint overall so less wastage;
- I personally find them less of a hassle to clean, but this comes down to personal preference;
What About The Side Feed Airbrush…?
A side feed airbrush is an airbrush where the paint cup feeds the paint into an internal mix paint atomisation chamber from the side of the airbrush.
It relies on a low pressure environment similar to the siphon feed airbrush to draw the paint into the airbrush.
👍 If a side feed airbrush is of interest to you check out this article which goes into them in detail and provides advantages and disadvantages relative to other airbrush types.
These are not overly common types of airbrushes and when looking for an airbrush to buy you will usually be presented with siphon feed or gravity feed airbrush.
Ultimately, Which Is Better Siphon Feed Or Gravity Feed Airbrush
Having owned both types I personally prefer a gravity feed airbrush for the following reasons:
- Less wastage
- Better spray pattern control
- Easier cleaning (personal preference)
But having said this it really is down the preference of the individual (you) and your unique airbrushing requirements.
If you find an airbrush model that has absolutely everything you want but it only comes with a siphon feed, then ignore my preferences above and grab yourself a siphon feed.
However if you find an airbrush that has absolutely everything you want but has the option of siphon feed OR gravity feed, my (possibly biased) recommendation is to go with the gravity feed. 👍