How Tanks Work... or rather When Tanks Don't Work

Jul 10, 2017 | 0

Written by Simon Wilson — July 10, 2017

Why does my juice taste burnt?

This is a very common issue for many people new to vaping, and the diagnosis is almost always the same- The coil has gone dry and is overheating.

This situation is called a "Dry-Hit" - it ranges from a slight burnt taste to a horrid acrid taste that can almost knock you back!

E-Cigarettes fall into various categories:

Drippers

These are very popular among the more experienced vapers, because they allow many different style coil builds, and endless tweaking to produce the style of vape the user enjoys. You don't get dry-hits with drippers, unless you vape them dry by accident. The vaper is in direct control of the juice flow.

Genesis Style Tanks

A true Genesis tank, popular in the early days (2012+) used a vertical Stainless Steel Mesh wick. There are a few modern style gennies which use cotton wicks with a horizontal coil. This style of tank uses the natural tilting of the device to keep juice flowing to the wick, so they tend to not suffer from dry-hits.

Pressure Difference Tanks

Probably 95% of all E-Cigarette tanks fall into this category, and are the subject of this article.

These tanks rely on there being a slightly higher pressure inside the tank to ensure juice gets transported to the coil via the cotton wick. The cotton wick serves 2 purposes equally. It is there to wick the juice to the coil, and also to act as a slow leak seal.

Equilibrium

This is the situation when you first fill your tank.

You will have already primed the coil with a little juice, so the cotton is now just holding back the juice that is in the tank, and pressure inside and outside is equal.

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Vaping Phase

When you vape, you draw air in through the airflow holes under the coil and up through the chimney into the mouth piece. As this air is moving relatively quickly it creates temporary low pressure under the coil.

So now we have a difference between the higher pressure inside the tank and the lower pressure at the coil.

This encourages the juice to flow to keep the cotton and coil saturated, giving a full flavour vape.

This vaping phase will continue until the internal tank pressure drops, as juice is used up, creating a partial vacuum inside the sealed tank. At some point this vacuum has to be recovered, because the tank pressure will continue to drop.

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Recovery Phase

Once there is sufficient low pressure vacuum inside the tank, the recovery phase will begin.

Once you stop vaping, atmospheric pressure returns under the coil, and the cotton seal will be broken so air can replace the vacuum created inside the tank.

This can be seen as bubbles floating up through the juice from the juice holes in the coil head.

If all works well, you should be back at Equilibrium ready to start all over again.

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What happens when they go wrong?

As you now see it is the cotton that controls both the wicking and the recovery pressure inside the tank. Most manufacturers pack slightly too much cotton into their stock coils. They do this because they cannot afford their tanks to leak, bear in mind their tanks have to be usable across a wide range of different juices with different PG/VG ratios. They err on the side of caution and test with the thinnest high PG juices.

This overpacked cotton tends to restrict the recovery phase, so the higher atmospheric pressure cannot leak back into the tank to equalise the partial vacuum inside. As you continue to vape the pressure difference gradually reduces, and eventually the low pressure inside the tank is equal to the low pressure your vaping is creating under the coil.

Stalled Phase

When the vacuum inside the tank is equal to the low pressure under the coil (created by vaping), there is no pressure difference, so the juice stops flowing to the coil.

The first sign of this is a reduction in flavour.

Most vapers instinctively turn up the power to get a better vape, of course this is exactly the wrong action.

Turning up the power simply vaporises the stagnant juice until none is left on the coil – THIS IS NOW A DRY HIT.

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Overpacked cotton seems to be the major cause of the tank stalling, and is the reason why some coils work better than others, in terms of flavour, even within a single box of coils, the manufacture varies.

Of course it is not the only reason, another major influence is the age of the coil. The cotton touching the coil will start to deteriorate and leave a carbon layer which contributes to the failure of recovery. This is why coils have variable limited lifespans.

Resolution

What you have to do, is to get that pressure difference back. Here are a couple of suggestions:

Open the tank

Simply open the tank to allow atmospheric pressure back in and release the partial vacuum.

With top fill style tanks, simply the act of starting to remove the filler cap will break the seal, and you will see air bubble up through the tank, releasing the low pressure.

With bottom fill tanks, you just invert the tank, start to unscrew the base a couple of turns to allow air in.

Primer Pulls

Another very effective method is to do a couple of dry “primer pulls”. This is where you draw sharply through the mouthpiece while fluttering your finger over the airflow hole, without firing the mod.

This primer pull, creates a strong low pressure under the coil, which is literally sucking juice to the coil. This creates a bigger vacuum inside the tank, so that when you stop drawing on the mouthpiece there will be sufficient pressure difference to break the cotton seal, allowing air to get back into the tank to release the low pressure inside.

Again you will see an air bubble or two rising through the liquid, proving the vacuum has been released.

The newer top-airflow tanks like the Nautilus X coils or Cubis Coils, are much harder to get back into equilibrium, and the only solution I have found that works is the "Open the Tank" method, which unfortunately can cause quite a bit of flooding. After a few vapes it will clear.

A better method is to open the tank, remove the coil, blow or shake out out excess juice form the coil, then reassemble.

Both of these methods above are only temporary fixes, and they will invariably stall again. It is unfortunately an inherent problem with the design. Even when building your own coils on an RBA type device, the old adage of "Less is More" holds true when using cotton.

<<< Simon Wilson - Tmax Juices - February 2017 >>>

How Tanks Work... or rather When Tanks Don't Work