Vacuum Testing Results - Tanks & RDAs

[Mikla]

Every once in a while a question comes up about what tank or RDA is good for Mouth-To-Lung (MTL) or Direct-To-Lung (DTL). I thought it might be interesting to put some science around the question so I made up a little crude test rig.

It consists of a Vacuum Pump connected to a tee fitting. A vacuum gauge is on one of the other legs of the tee and the final leg is connected to a drip tip (except where noted the same drip tip with a 15/64" bore is used for each test).

A base line vacuum is measured before connecting to the tank/RDA. Then the drip tip is assembled on to the tank/RDA. The vacuum is measured at various air flow levels based on how far the air flow control is open (usually at the base of the device). For those devices that also had top air flow controls, they were left closed.

Doing this I was able to generate some plots for the various devices I had on hand (and not currently filled with juice). These devices were all empty and had no cotton in the coils (though some testing showed it made no difference if there was cotton or juice in the device).

Based on the plot below, the Hurricane and the Taifun provided similar vacuum while providing fairly decent air flow control across the range of 0 to 100% air flow. The 100% air flow vacuum of -9 or less indicates some significant vacuum is required to pull air through the device (no surprise for anyone that has used these devices). The little offset in the Hurricane curve is do to the hole configuration (either single or dual depending on position of the air flow control ring).

The Kayfun has no air flow control but has the lowest vacuum of -16 inHg (or hardest to draw air through).

The Velocity RDA was difficult to measure do to the slots and holes in the device. There really was not much difference anyway from 0 to 100%. There was a lot of air flow leaking around the air holes and slots even when completely closed on the device I was testing.

The rest of the devices all had a significant knee in the curve around 25%. Above that number and changes in air flow had minimal effect on the vacuum. But below that number the air flow vs vacuum was pretty linear. This could mean they are more difficult to adjust for MTL vapers to get a decent vape.

Given all this (need more devices to test) it seems that a good MTL device will have a 100% air flow of less than -8 inHg and/or have a flatter curve across the air flow opening range.

Well that was fun... Feel free to reinterpret or use for your own purposes... Chart...

 

[Mr.Mann]

Very cool indeed!

 

[Andromendous]

I dont understand this. So, lower number is better for wicking?

 

[Mikla]

It is not really related to wicking. It is just an attempt to associated some numbers with what could be considered at MTL versus DTL device (tank or RDA). I think common sense tells us if our cheeks suck in when we try to draw on a tank/RDA then it is more likely to be a better MTL device.

That sucking in is creating a vacuum. The chart just indicates what that vacuum is at various air flow settings of a tank/RDA.

I arbitrarily picked -8 inches of Mercury (inHg) or lower at 100% air flow as the level defining a good MTL tank/RDA. Will do more testing with a few more tanks/RDAs that I have and that number may change.

 

[Mr.Mann]

It is not really related to wicking. It is just an attempt to associated some numbers with what could be considered at MTL versus DTL device (tank or RDA). I think common sense tells us if our cheeks suck in when we try to draw on a tank/RDA then it is more likely to be a better MTL device.

That sucking in is creating a vacuum. The chart just indicates what that vacuum is at various air flow settings of a tank/RDA.

I arbitrarily picked -8 inches of Mercury (inHg) or lower at 100% air flow as the level defining a good MTL tank/RDA. Will do more testing with a few more tanks/RDAs that I have and that number may change.

I've always wondered how to quantify how 'much' airflow one device has over the next. I don't know if this does that exactly, or if I would know it even if I saw it, but it's the first I've seen that even really approaches the notion.

 

[Mikla]

Yes, there is a direct correlation between pressure drop (vacuum), air flow hole size (orifice area) and air flow (flow rate).

Air flow increases if either or both of the hole size or pressure drop increases. Or another way to look at it is in order to draw the same amount of air through a tank/RDA you have to suck harder (larger vacuum) on a tank/RDA with smaller air holes.

Just for information:
Pressure Drop (dP) - Difference in pressure at two different points in a flow (air or fluid). Think of a balloon. The air is at a higher pressure inside the balloon. When you are letting the air flow out of the balloon the difference between the pressure in the balloon and outside the balloon is the pressure drop. Side note: high pressure always attempts to go to low pressure (that is why the balloon deflates and also a primary reason why airplanes fly). For a tank or RDA this would be the difference in pressure between the air around the tank/RDA and the air around the coil. In the case of the above chart this is the value of the vacuum.

Orifice Area (A) - This is simply related to the diameter or size of the opening between two points in an air flow. In the balloon example, the neck (part you blow into) of the balloon acts as the orifice so the inner diameter of that neck is the diameter of the orifice. For tanks or RDAs, it would be the combined area of any air flow holes that allow air to blow across the coils.

Flow Rate (FR) - The volume of fluid (or gas/air) that moves past a particular point in the flow in a given time. Typically for air this is Cubic Feet per Minute (CFM). So 1 CFM means that 1 cubic foot (a box 1ft x 1ft x 1ft) of air moves past a point in 1 minute. For a tank/RDA this would be how much air you are sucking through the drip tip. Side Note: When vaping you are probably taking in somewhere around 0.25 - 0.5 CFM.

Not sure this helps, but it did feel good to exercise my brain...

 

[tejas]

Interesting study.
I notice you have listed the "Kayfun Lite v4". I have a Kayfun Lite, and hate it, because of the restricted air flow. I describe as 'trying to suck a marble through a juice box straw. I love my Kayfun v4, after opening up the air flow a bit.
But I was unaware of the Kayfun Lite v4.

 

[Mikla]

Yep, it's a clone and definitely is restrictive but I don't find it that bad. It is what I am using right now (my other tanks/mods are scattered somewhere else at the moment)... 1.3ohms at 20W and is OK flavor and decent vapor. Not something I use everyday, but it is a change and easy to fill so I can change juices pretty quick with it.