On a vertical plunger pump, where is the plunger attached?

In a vertical plunger pump, the plunger is connected to the cross head. The cross head acts as a component that converts the linear motion of the plunger into a pumping action, facilitating the movement of the working fluid through the pump. This connection is integral to the operation of the pump, as it ensures that the plunger can move efficiently and create the required pressure to drive the fluid.

The other components listed do not serve this purpose. The flywheel, for example, is typically part of systems that help maintain momentum or smooth out the operation, particularly in engines or rotary systems, but it is not involved in the direct functioning of a plunger pump. The frame provides structural support for the pump assembly but does not interact with the plunger in terms of fluid movement. Lastly, the piston is a different component that is found in other types of pumps and is not part of the plunger mechanism in this specific type of pump. This makes the connection of the plunger to the cross head the correct answer.