I dont buy that many products in aerosol cans, so maybe Im strangely ignorant of a change in the technology that has been around for a while, but when I bought some shaving gel last week, I noticed something that was new to me.
On each can, in the center of the concave steel bottom, is a tiny black plastic nub
or plug. When pressed to one side, even gently, I hear a hiss of escaping propellant. At first I thought that this was just an artifact of how the cans were filled, and I had a defective seal. But all 4 cans in the package (Costco is my friend) do this.
Is this some new safety feature (a pressure release valve) or maybe something to
facilitate recycling?
I think the key is that it’s used in non-aerosol cans. I have a pressurized can of silicon sealant that has such a plug.
A liquid will settle to the bottom of the can. A pick-up tube can reach down there, the propellant will be at the top, and it will come out as an aerosol. Both propellant and liquid can be loaded from the top during manufacture.
Thicker goo, like shaving cream and silicon sealant, doesn’t settle easily and doesn’t travel through long pick-up tubes easily. The goo can be loaded from the top, but the propellant needs to be at the bottom. The plug seals it in and isn’t meant to be pressed to the side.
So it is an artifact of manufacture, but it’s not defective. Leave it be and it won’t leak.
Your done the equivalent of depressing a tire air check valve. Don’t do that, you’ll at best throw away four full cans of gel with no pressure, and at worst end up with the gell shooting out the bottom where the plug popped out. Now go search for why shoe polish cans have a sealed hole in the lid, it’s worth it.
I’ve seen cans of aerosol shaving cream with the plug, and a little bit of foam squirts out when it’s pressed to one side.
The gel cans work differently. There’s a plastic bag filled with gel inside the can. The propellant is in the space between the can and the bag, and exerts pressure on the bag.