Automatic Transmission Valves
At the heart of the automatic transmissions hydraulic control system is the valve body. It usually consists of three parts: the separator plate, the transfer plate and the valve body itself. These three parts are installed on the transmission as a single unit. It will be constructed of either iron or aluminum.
Inside the valve body you will find three different types of valves: the poppet, the check ball, and the spool valve.
The poppet valve can be a ball or a flat disc and usually has a stem that acts as a guide for the valves opening or closing. This valve like so many others acts as a port to either block or allow the flow of fluid.
A check ball valve sits in a seat in the valve body that allows or blocks fluid according to the direction of its flow. These check balls can be either normally open or closed depending on the application and manufacturer.
The spool valve is by far the most common valve found in automatic transmissions. They resemble a spool of thread with large areas used to block fluid flow called lands and stemmed areas called valleys. At each end of the valve is located a reaction area. This is the area where fluid pressure, linkage, or a spring acts as a force to activate the valve.
