The term "injection valve" is PULSAIR terminology, not valve terminology. The valves are generically called 3-way, 2-position, remote-air-piloted power valves.
A 3-way valve has three ports or connections: inlet, outlet, and exhaust. On our injection valves these ports are labeled IN for inlet, CYL for outlet (it actually is short for "cylinder"), and EXH for exhaust.
A 2-position valve is a valve that has two usable flow paths. In the case of our injection valves, when the valve is open the path is from the inlet port to the outlet or cylinder port; when the valve is closed, the path is from the outlet port "back" through the exhaust port.
PULSAIR injection valves are "normally closed" or N.C. valves. This means that the inlet port is blocked until the valve is actuated, at which time the spool shifts and opens the path from the inlet to the outlet port, producing the air flow into the tank. Valve actuation is accomplished by sending a "pilot signal" to the valve i.e. air is sent to the valve actuator from the controller, hence the term "remote-air-piloted". These pilot signals are sent through the 1/4" black nylon tubing that is supplied with the controller. When the pilot signal is vented the valve closes again. The length of time the valve stays open, of course, is determined by the dwell setting on the controller normally about a 1/2 second.
Its reasonable to ask why PULSAIR uses a 3-way valve, since we plug the exhaust port, which effectively makes it a 2-way valve. The answer is that these valves have the operating characteristics we need, are readily available, and are reasonably priced. So it makes sense to use them in this modified condition.
These valves have the highest flow rate of any similar valves on the market today. Furthermore, they are quick acting. These two features combine to produce the pulses of air that are key to generating the PULSAIR bubble and subsequent, fantastic mixing effectiveness.
We tried using these valves as three-way valves without the plug during nuclear waste mixing simulations conducted by Battelle Northwest. Battelle believed there could be an advantage to opening the exhaust port to atmosphere because liquid would fill the injection pipes between pulses and perhaps increase the mixing force when expelled by the air pulse. In fact, it proved to have no effect on the mixing. As a result, we'll keep plugging the exhaust port because it minimizes the liquid contact inside the piping.
There are situations where the PULSAIR is located in a harsh environment . It can be advantageous in these situations to house the injection valves in the same enclosure as the pneumatic controller. This requires a larger housing. Controllers with injection valves housed internally are denoted by an X at the end of the model number. See Internal Injection Valves.