In a vertical mount piston pump, where does the lubricant enter the cylinder during the piston's downstroke?

In a vertical mount piston pump, the lubricant is typically introduced into the cylinder during the piston's downstroke through the sight well. During this downstroke, a vacuum is created within the cylinder, allowing the lubricant to be drawn in and properly lubricate the internal components of the pump. The sight well serves as an observation point that can also facilitate the flow of lubricant into the cylinder, ensuring that the piston and its mechanism remain well-lubricated for efficient operation.

The other options do not correctly describe the source of lubrication for the cylinder during this phase of the pump's operation. The drive shaft, while crucial for the pump's mechanics, does not directly provide lubricant to the cylinder. The suction line is responsible for bringing in the fluid being pumped, not the lubricant. The discharge outlet is where the pumped fluid exits the pump; it is not a pathway for the lubricant entering during the downstroke.