Aqueous ammonium hydroxide machines are more commonly used for low volume jobs, especially for engineering or architectural applications. The bottle is connected to the machine with two or three plastic hoses. One hose bubbles air into the liquid to drive the ammonia gas out of solution, another hose pumps the vapor from the bottle to the developer tank. A third hose may be used to return the ammonia vapor to the bottle. On most aqueous ammonia machines, there is no separate power control for the pump.
Ammonia vapor is pumped into the developer as long as the machine is running.
On some machines, the pump speed can be adjusted to a high or low level. In the high position, air is bubbled into the ammonia to drive off the maximum amount of vapor. The high position is used when the ammonia is old and weak or when running large prints at rapid speed. A filter device is usually attached to aqueous ammonia machines to collect the ammonia exhaust. The filter may be in the form of a cartridge that fits into the machine, or an external carbon adsorption canister that is attached to the exhaust.