Would lotion pumps work in a vacuum? I'm just trying to understand how a lotion pump works. I watched this video and it's explained that it's due to the difference in air pressure.
https://www.youtube.com/watch?v=EJVL5zXIPLA&ab_channel=JenWang
Does this mean that if we put a lotion pump in a vacuum, when we press on the head, the liquid won't be able to come up because there's no air? For some reason, instinctively I thought it had to do with the pump literally squeezing the liquid out due to the decrease in volume since there's nowhere for the liquid to move to.
 A: The pump has a reservoir (the bottle part) and a chamber (the short fat cylinder on the straw and spring assembly).
If the chamber is filled with liquid, depressing the actuator closes a valve at the bottom and opens a valve at the top and squeezes the liquid out through the top by reducing the amount of space available for the liquid inside the chamber.
When the actuator spring pushes the actuator back up into its resting position, the valve at the bottom opens and the valve at the top closes. Gas pressure inside the reservoir pushes liquid from the reservoir up into the chamber.
If you took away the gas pressure (and somehow kept the liquid from boiling fast enough to replenish it), the pump would dispense the one squirt of liquid that was stored inside the chamber, but the chamber would not refill, so that would be the last squirt.
A: If you take a brand new lotion pump bottle from Earth and bring it to a vacuum, your first issue would be that the bottle might explode, since there's no outside pressure pushing in. So let's assume the bottle is strong enough for this not to happen.
You must also ensure that your vacuum is at a normal temperature. Most any vacuum in a lab on Earth can have this property (since it may be at thermal equilibrium with its surroundings), but out in deep space it's 3 Kelvin. If it's too cold there's a high chance then that any liquid inside the bottle will freeze solid. The pump components (plastic, rubber, and metal) may also become extremely hard and brittle, and may not work/move anymore.
Assuming the vacuum is kept at a reasonable temperature... Usually with new lotion bottles you need to twist the top a bit to "unlock" the pump. As soon as you unlock it, all air inside the piston will rush out, and depending on the liquid/lotion that may start coming out as well, until the pump comes all the way up and seals the chamber. This is what you were mentioning, I believe. It would basically be like somebody is sucking infinitely hard (i.e. creating perfect vacuum in their mouth) through a straw.
