The hydraulic pump converts the mechanical energy of the prime mover into hydraulic energy for system use. Hydraulic energy is the combination of pressure and flow required by the actuator to perform useful work. It is important to understand that hydraulic energy is both pressure and flow, because one cannot do the job without the other. The pressure consists of the stagnant fluid,hydraulic pump and the flow will have no energy to move the fluid alone. The hydraulic pump pushes the fluid,hydraulic pump and for that matter, the fluid can be considered as a solid because it is transported throughout the machine and then pushes the actuator to move the load. People with motion control will let me point out that oil is compressible, but this is another blog discussion.
The point is that the pump may push on sand, ball bearings, or other solid media that can shape its container,hydraulic pump and the result is still force transmission. The transmission of force is indeed synonymous with hydraulic pressure,hydraulic pump and it is also the basis of Cosford's law, which states that "pressure makes it disappear,hydraulic pump and flow is the rate at which pressure can be generated." For fluid movement, pressure reaches the position of the pump; always. Faced with the fallacy that pressure is fluid,hydraulic pump this is wrong. The pressure will rise to the pressure needed to overcome the downstream resistance, but if the pressure is not activated at the pump,hydraulic pump the fluid will move backwards.
The pressure in hydraulic pressure is the result of Newton's third law of motion,hydraulic pump which makes every action have an equal and opposite reaction force. The reverse force can be a loaded cylinder or a flow controller,hydraulic pump and the pump doesn't care. It will continue to push the fluid to overcome the resistance as the pressure increases,hydraulic pump even if this causes the prime mover to overload.