I have had the same problem with the air pump type of spray bottles (
that a stream comes out instead of a mist - after a while). My friend
has a Pampered Chef pump and has had no problems.
Also, an air pump isn't necessary for something as light as liquid
aminos - you could use any spray bottle, like the ones sold in drug
stores for $1-$2(they work just like a windex bottle or a bottle of
non-aresol hair spray).