The 
Scuba Mask and 
Scuba Tank are two pieces of Mekanism gear that’ll let you breathe underwater when they’re worn together. The Mask goes on your head and the Tank on your chest, and the Tank has to be filled with Oxygen and switched on before any air will flow, as it starts turned off.
A full Tank holds 24,000 mB of Oxygen, which lasts for up to 20 minutes while it’s flowing. As well as keeping your air meter full, the set will block Poison and other magic damage and make potion effects wear off much faster, which makes it useful on dry land too.
How to Get It
You’ll need to craft both pieces, as neither does anything without the other. The Scuba Mask is made from 3 
Steel Ingots, 2 
Glass and a 
Basic Control Circuit, whereas the Scuba Tank takes 3 Steel Ingots, 2 
Infused Alloy, a Basic Control Circuit and a 
Basic Chemical Tank.
Neither piece has any armor value, so you’re giving up a helmet and a chestplate while they’re on. The Mask is able to take the Aqua Affinity enchantment, though, which is worth adding if you’ll be mining underwater with it.
How to Use It
Filling the Tank with Oxygen
Oxygen comes from an 
Electrolytic Separator, which makes it alongside Hydrogen when it splits Water. To fill the Scuba Tank, place it in the item slot under the Oxygen tank on the right of the Separator’s screen, or in the top slot of a Chemical Tank that’s holding Oxygen, which is the one marked with a plus.
It takes in 16 mB a tick, so an empty Tank will be full in 75 seconds if there’s enough Oxygen stored up. A Separator without upgrades only makes 1 mB of Oxygen a tick, though, so it’s quicker to fill from a Chemical Tank that’s been left to collect it.
Right-clicking a tank with the Scuba Tank in your hand won’t fill it, as it has to sit in one of those slots. A 
Chargepad or an Energy Cube does nothing for it either, as it holds a chemical and not energy.
Turning the Air On
With both pieces on, press the 
Chest Mode Switch key, which is G by default, to start the Oxygen flowing. The Tank’s tooltip shows whether it’s Flowing or not, and you’ll hear the air once it’s on. Nothing will happen if you forget this step, as a Tank that’s switched off is ignored even when it’s full.
While it’s flowing, the Tank uses 1 mB of Oxygen every tick, and that’s true whether you’re underwater or standing on land. It also spends a little more whenever your air meter has dropped, to bring it back to full, so you’ll want to turn the flow off again once you’re out of the water.
JetpackPoison and Potion Effects
While the Scuba Mask is on and the Scuba Tank is flowing with Oxygen in it, magic damage is cancelled completely. That covers the damage from Poison and from Instant Damage potions, so a Witch or a Cave Spider is a lot less of a threat, although Wither damage isn’t included and will still hurt.
Potion effects also run out about 10 times faster as long as your air meter is full. That’s any effect that Milk would normally cure, so it’ll clear things like Slowness and Mining Fatigue quickly, but it shortens the good effects you’ve given yourself as well. Once you’ve got the set working, the 
Flamethrower is another piece of gear that fills from a machine in the same way.
FAQ
The Scuba Tank is filled with Oxygen from an Electrolytic Separator, by placing it in the item slot under the Separator’s Oxygen tank, or in the top slot of a Chemical Tank that has Oxygen in it. It holds 24,000 mB and fills at 16 mB a tick, so it’ll take 75 seconds from empty.
It’s most likely that the Scuba Tank is switched off, as it starts that way, so press the Chest Mode Switch key (G) to turn the flow on. Otherwise the Tank might be empty, or it isn’t in the chest slot, as the Mask needs a Tank with Oxygen in it to do anything.
A full Tank holds 24,000 mB and uses 1 mB a tick while it’s flowing, which gives up to 20 minutes. It’s used at that rate on land as well, and a bit more goes on refilling your air meter, so turning the flow off when you surface will make it last longer.
They both go in the chest slot, so only one of them is able to be worn at once and you’ll have to swap between them. Later on the MekaSuit gets around this, as it can take a 
Jetpack Unit on the Bodyarmor and an 
Electrolytic Breathing Unit on the Helmet together.
