What type of valve body seals on the down stroke?

The correct answer is related to how certain valve types function when they are actuated. A direct acting valve is one that seals in the down stroke, meaning that when the actuator pushes down, it directly closes the valve, creating a seal that stops the flow of fluid or gas. This type of valve operates on the principle that the force of the actuator directly moves the valve into its closed position.

In the context of the other options, a reverse acting valve typically has a different operational mechanism; it may require an opposite action to close and therefore does not seal in the same way on the down stroke. Single sealed and double sealed valves are terms that refer to the configuration of the seals themselves rather than the direction of operation or how the valve seals during movement. Thus, the key characteristic of direct acting valves is that they effectively create a seal during the down stroke, enabling them to control flow efficiently.