Siphon fed airbrushes not siphon fed?

LOL!

Siphon is still the correct terminology to differentiate between a gravity and siphon feed airbrushes. Gravity feed requires nothing other than gravity to feed the paint to the needle, where siphon feed requires air pressure to start the siphon process.

Besides, Hydrostatic Pressure feed is too much of a mouthful!

Some people have far too much time on their hands. Probably a nerd physicist with nothing better to do.

Actually that makes since and siphon fed airbrushes actually aren't even based on the flawed dictionary definition. A siphon moves from high to low, so it is obviously based on gravity. If you have ever tried to siphon fluid you know you have to put the hose exit below the fluid level or you will empty the container you are trying to fill.

Vacuum or venturi airbrush would probably be a more accurate term, since vacuum will raise a fluid. High pressure (atmosphere) will push a fluid towards an area of low pressure even if it is higher than the source. Of course a gravity fed air brush also benefits from the effect.

Hey I run fire pumps for a living so I have to be familiar with these concepts, however I never took the time to think about the physics of a siphon, I'll look smarter the next time I each a pump ops class.

Not that I'm suggesting we change the well established use of siphon for a "siphon" fed airbrush.

MikeV

Some people have far too much time on their hands. Probably a nerd physicist with nothing better to do.

As a retired nerd, I resemble that remark. 

By the way, I think simpler and more accurate terminology would be: bottom fed, side fed, and top fed.

Now, who wants to write all the airbrush manufacturers and tell them to quit trying to fool us? 

Don

Well, Badger uses both siphon and bottom, so they're already on board!

I personally don't like bottom feed. Bottom feeder sounds like a lawyer (no offense to any lawyers out there! Well, maybe a little!).

HEY!  I'm a lawyer...but i use a gravity fed a/b - does that make me a *better* type of lawyer?

Chris.

LOL!

Don Wheeler

Just for those who delight in useless trivia:   According to this article, siphons work by gravity, not air pressure differences.  Therefore, siphon fed airbrushes are not really siphon fed.  I wonder, what would the correct term be, and why are the airbrush companies lying to us? 

Don

The English word "siphon" came from Greek that meant pipe or tube. I believe most of the siphon feed aribrush have a tube in it. So, the airbrush company might not have lied to us.

Siphon is used also in zoology for tubular organ, especially of aquatic invertebrates such as squids or clams, by which water is taken in or expelled. In verb, it means suck off by any means. For example, "to siphon off profits into a secret bank account".

Siphon does not work in vacuum. The liquid was "pumped" by the atmosphere pressure difference created by gravity, but not gravity directly.

Ok, ok, I am splitting hair.

Well, whatever we end up calling it, since most of us prefer gravity fed, we should be able to agree that siphon fed airbrushes suck.

Sorry, couldn't resist that!

A "siphon feed" airbrush works wonder in Don Wheeler's hand. I can't say it sucks.

Then how does it pick up the paint?

On second thought, the aribrush company does lie to us. All airbrushes "siphon" paint into the nozzle to "spray" out.

There is no such thing as a "gravity feed" airbrush. If so, we could have save the dollars for the compressor and buy more models instead. You can test it. If you have a "gravity feed" airbrush, turn off your compressor and see how much paint will come out. Not nearly enough under gravity-feed only.

All airbrushes "siphon" paint into the nozzle by the low pressure created by the air stream instead of a lower gravity point like the traditional siphon. Gravity either works against it in airbrush with bottle below the body or assist it with cup above the airbrush body. 

(The noun "Siphon" is a tube or conduit bent into legs of unequal length, for use in drawing a liquid from one container into another on a lower level. The verb "siphon" can apply to drawing fluid using lower pressure created by a siphon or other means.)

Don Wheeler

According to this article, siphons work by gravity, not air pressure differences. 

If so, siphon should work in a vacuum. But it is NOT the case.

Alright, enough hair splitting. This post is for nerds only.

Bgrigg

Then how does it pick up the paint?

Online, with it's credit card!

I am in tendency to agree that siphon is incorrect, in  the same manner that gravity fed is also incorrect. like suggested it should be top or bottom fed.

Neither the "Siphon" or "Gravity" brushes & guns operate in accordance with their names, both work using an aspirator / eductor jet pump & utilise the Venturi effect - ?

If correct, this means that we have the Italians to thank for all the wonderful Japanese, American, European & Chinese spray toys we use! It also means that the Gravity & Siphon products are really not that different, although I still will not be rushing out any time soon to get a bottom feeder.

Isn't this merely a restatement of the old article about whether a vacuum (or reduced pressure) sucks or pushes?

They both work in the same way. They all suck! One just has a cap (jar bottom) on the reservoir to keep the paint in.

I think siphons suck (personal opinion).

I have noticed that there seems to be whole lot of argument all over the interweb in regards to weather a siphon can work in a vacuum or not. I understood that a siphon relied on hydrostatic pressure alone, but looks like it may rely on atmospheric pressure to start the process?

It's pretty amazing that in this day & age that argument still goes on about something that on the surface looks so simple?

I suppose surface tension is another discussion altogether.

keilau

 

If so, siphon should work in a vacuum. But it is NOT the case.

Alright, enough hair splitting. This post is for nerds only.

Ah, but doesn't atmospheric pressure decrease as altitude increases?  That would mean the air pressure on the tank would be less than the air pressure at the end of the hose.  The difference would tend to push the water back up the hose.   The area exposed to air is much greater in the tank, but pressure is measured in pounds per square inch (or other units) so that shouldn't matter.

I've seen arguments both ways on whether a siphon works in a vacuum.  I would vote yes, but I wonder if anyone has ever actually tried it.  I love the picture.  It looks like something by my hero, Rube Goldberg.

Boy, this is getting nerdy. 

Don

That pic is a drawing by Slug Signorino, who illustrates for Cecil Adam's syndicated column "The Straight Dope".

Siphons do work in vacuums, but only under special circumstances:

Surprisingly, experiments have indeed shown that siphons can operate in a vacuum, provided that the liquids are pure and degassed and surfaces are very clean. However, typical practical siphons make little or no use of liquid tensile strength to achieve their effect, instead relying on gravity.

Personally, I don't think the "new" answer is 100% correct, either. I suspect that it's a combination of air pressure, gravity, and the tensile strength of the material being siphoned. After all a siphon is limited to the same height restrictions a barometer is, and those rely completely on air pressure.

Gravity fed works as a term to describe that form of airbrush, as the paint medium is fed via gravity. The airbrush needs air pressure to create the venturi effect to atomize the paint, but paint will drip from the end of an opened airbrush through gravity alone.

Siphon is used to mean a liquid passing along a tube, and siphon fed airbrushes do that, so I'm sticking with the name. If one wants to get nit-picky "Venturi Siphon" would suffice as a term.

Don Wheeler

 

keilau:

 

Alright, enough hair splitting. This post is for nerds only.

 

 

Ah, but doesn't atmospheric pressure decrease as altitude increases?  That would mean the air pressure on the tank would be less than the air pressure at the end of the hose.  The difference would tend to push the water back up the hose.   The area exposed to air is much greater in the tank, but pressure is measured in pounds per square inch (or other units) so that shouldn't matter.

I've seen arguments both ways on whether a siphon works in a vacuum.  I would vote yes, but I wonder if anyone has ever actually tried it.  I love the picture.  It looks like something by my hero, Rube Goldberg.

Boy, this is getting nerdy. 

Don

Boy, you are one smart nerd. I was just trying to split hair and out nerd you. The siphon action is driven by the pressure difference of a liquid height between the inlet and outlet of the siphon. In a sense, you are right the first place saying that siphon is gravity driven.

The picture is just for fun. It is NOT a real representation of siphon. Siphon does not work in vacuum because the liquid boiling point will be so much lower than room temperature, the liquid will evaporate before the siphon starts. It is a theory vs. reality question. I am an engineer and naturally drawn to the reality. If someone discovers a siphon working in vacuum video, it will be amazing to see.

It is better nerdy than nasty.

I got nothing to add to this conversation...

keilau

It is better nerdy than nasty.

I'm guessing this is being directed at me. Tell me, what are you trying to achieve?

Bgrigg

Personally, I don't think the "new" answer is 100% correct, either. I suspect that it's a combination of air pressure, gravity, and the tensile strength of the material being siphoned. After all a siphon is limited to the same height restrictions a barometer is, and those rely completely on air pressure.

When you say a siphon is limited to barometric pressure I assume you mean the lift (the part going up and over), I can assure you it works fine if the down part exceeds the roughly 30 foot theoretical limit. We use something called a gravity sock which is nothing more than a glorified siphon and it wil provide water hundreds of feet below the source.

We rarely use it due to the very specific requirements, but it allows a creek or pond above a fire to supply water through small fire hose to a fire located on a hillside below the water source. A collapsing cloth funnel (the gravity sock) is a lot easier to hike in than a 50lb portable pump along with the fuel and such needed to keep it running.

It appears to me the claims that a siphon doesn't work in a vaccuum have more to do with the physics of liquids and the inability to start the process (can't create an area of lower pressure to begin the process if you are already in a vaccum), than any proof that a siphon uses atmospheric pressure to move from pool A to pool B.

Aaron,

Yes, I meant the initial lift. According to the article on Wikipedia:

This is the maximum height that a siphon will work. It is simply when the weight of the column of liquid to the intermediate high point equates to atmospheric pressure. Substituting values will give approximately 10 metres for water and 0.76 metres for mercury.

Are you saying that the gravity sock will allow water to siphoned uphill higher than 32' before making the turn to the delivery side of the hose, without mechanical means? 

Bgrigg

Aaron,

Yes, I meant the initial lift. According to the article on Wikipedia:

This is the maximum height that a siphon will work. It is simply when the weight of the column of liquid to the intermediate high point equates to atmospheric pressure. Substituting values will give approximately 10 metres for water and 0.76 metres for mercury.

Are you saying that the gravity sock will allow water to siphoned uphill higher than 32' before making the turn to the delivery side of the hose, without mechanical means? 

No, the gravity sock will allow very little lift because it is using a soft hose, it is also limited because you are using the funnel to fill the hose to create the siphon which limits height to the persons head height.

I have drafted with a pump until water is flowing down the hose then used the siphon effect to continue the flow. With nearly 1 psi for every 2 foot drop you get good pressure without the pump fairly quickly on a steep hill, a 700 foot drop which is not unusual on longer hoselays (I've pumped on 5000-6000 foot lays a few times) will quickly start to burst hose using nothing more than gravity since hose is only tested to 250 psi.

I was just making sure you were only refering to the lift, which is dependant on air pressure to get the process started (you have to have areas of low and high pressure). A siphon is just a simple pump driven by gravity instead of your arm or a motor so of course has to follow the same rules of drafting. To beat the height we use an ejector (venturi pump) which will allow up to 200 feet of "lift" but that is not really the same since water is being pumped through the venturi then assisted back up, the real lift is only a few inches.

Sorry I geek out on pump stuff, I love to supply water where lesser operators say it can't be done.   

Ah, I understand. Are you a firefighter?

Back in the 70s I helped build a gravity well for my sister. She and her husband were 'living off the land' far beyond the reach of electricity. Ah, the heady days of The Whole Earth Catalog and Country Comforts!.

We had found a spring 150' behind and 100' above their house and installed a cistern as a holding tank, then ran dug a water line into her home. Using your measurement of 1 lb of psi per 2' drop, her pressure was 50 psi. We didn't test it, but I don't remember it ever running out of water.

Yes, I'm a fire captain with the National Park Service. I took the promotion for the money and fame , but my real love is running the pumps. As fire hydrants are rare in the forest you need to be creative finding suitable water sources. 

In my salad days I did a couple of summers fighting forest fires in the wilds of BC. There certainly was a dearth of hydrants, as I recall. Most of the time I had a squirt tank on my back and a shovel in my hand and I was putting out sparks.

One of my nieces got run over twice by a water truck while sleeping on the ground during a fire in Plumas County. Why her crew wasn't in a safe sleeping area is beyond me. She's ok now but her hiking, not to mention CDF days, are over.

Be careful Aaron.

I heard about that, and was rather confused about how it occured as well. The people running the fire camps are usually pretty obnoxious about where people sleep in the name of safety (I swear some of them find the most out of the way uncomfortable piece of ground for us to sleep on) .

I know with injuries like that full recovery is unlikely, but glad to hear it sounds like she is doing a lot better.  

I have made it 18 years without a major injury to myself or anyone working for me and am doing what I can to make sure I make it the remaining 8 in one piece and in a condition to enjoy retirement. Hey I have a lot of models to finish so I can't let myself get too beat up.