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...
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...