This a practical problem for the design of a system which uses a water driven hydraulic motor. Assume a 100 gallon tank is filled with water, constantly filled further pressurized by a pump to 500psi Assume a hydraulic powered motor which operates with intake required at 200psi, flow of 10 gallons per minute. How can both pressure stepped down, and flow controlled to the required input rate at the same time? Assume there will be a vave which controls the diameter of the opening at the bottom of the water tank through which the water flows. The pipe connected the two can be of arbitrary volume/diameter, but the pipe connector at the motor end is say 5cm in diameter. Is this possible, or are pressure and flow equal to some constant which makes fixing both at arbitrary values impossible? If there are relevant equations can you please point me in the right direction? Thanks.