Question regarding keeping air pressure in scuba tank.

[Nathan Doty]

Raising the temperature increases the amount of water it could hold, but the air still has the water it had when it was heated so the RH drops. Raising the pressure reduced the amount of water it can hold, so the RH rises and the some water drops out. If you drain that water shop air is dryer than atmospheric air.

Yes, that's one of the reasons I drain. But it's still wetter than the air in a cylinder. Dryer than atmosphere is still wetter than we dive with.

Any moisture in the shop tank makes the incoming hot air wetter than regular, cool air and draining doesnt remove all water, just most of it. The only way to have similar humidity levels is to walk away every time the compressor kicks on and wait a day until everything cools and some of that moisture condensate out. I could install a cooler between compressor and tank but im content just draining periodically and saving the $$$$.

 

[BRT]

Yes, that's one of the reasons I drain. But it's still wetter than the air in a cylinder. Dryer than atmosphere is still wetter than we dive with.

Any moisture in the shop tank makes the incoming hot air wetter than regular, cool air and draining doesnt remove all water, just most of it. The only way to have similar humidity levels is to walk away every time the compressor kicks on and wait a day until everything cools and some of that moisture condensate out. I could install a cooler between compressor and tank but im content just draining periodically and saving the $$$$.

But air in the piped shop system eventually cools, starting in the tank. Because it is still under pressure and capable of carrying less water this is a great opportunity to auto drain the water. In my shop air system I have hundreds of feet of copper air piping and drain valves drops all over and at the ends of runs. Where water shows up I put auto drains. After years of not checking I can open one of my end of line drains and just get a puff of vapor. On my scuba compressor I run the air out of the compressor through a coil in a bath of 34 degree antifreeze and then to the condensate trap. That cold air at high pressure won't hold much water and I auto drain it from the trap.

 

[Nathan Doty]

But air in the piped shop system eventually cools, starting in the tank. Because it is still under pressure and capable of carrying less water this is a great opportunity to auto drain the water. In my shop air system I have hundreds of feet of copper air piping and drain valves drops all over and at the ends of runs. Where water shows up I put auto drains. After years of not checking I can open one of my end of line drains and just get a puff of vapor. On my scuba compressor I run the air out of the compressor through a coil in a bath of 34 degree antifreeze and then to the condensate trap. That cold air at high pressure won't hold much water and I auto drain it from the trap.

My 2 car garage and hundreds of feet of copper cooling plus drops and drains all over... doesn't really belong in the same paragraph I'd like a cooler but in a few months when my 56 is done my big compressor goes back to being used rarely. I'll probably diy a cooler before I get to painting though. I see some homebrew I'm stupid style oil coolers with an electric fan will likely work well enough for what I need.

Im in florida so I start pretty humid .I go through a lot of air using the blast cabinet, after the compressor fires up it comes out hot and wet.

 

[BRT]

My 2 car garage and hundreds of feet of copper cooling plus drops and drains all over... doesn't really belong in the same paragraph I'd like a cooler but in a few months when my 56 is done my big compressor goes back to being used rarely. I'll probably diy a cooler before I get to painting though. I see some homebrew I'm stupid style oil coolers with an electric fan will likely work well enough for what I need.

I go through a lot of air using the blast cabinet, after the compressor fires up it comes out hot and wet.

I considered plumbing in a radiator of some sort just past the compressors but the system I have works very well.