The basic answer as to how to simulate a pump in simulink is to write the system of equations that defines the relationship between the input, voltage or torque or force, given to the pump and the output, pressure or flow. Then translate the equations into a hand written block diagram. From this diagram it should be easy to see what components one needs to connect to one another in simulink to create the simulation.
More information generally means a more concise answer...
Hope this helps.
BsK