We are given that a 4 inches cylinder is required to produce 2000 lbf of force. To determine the pressure we will use the following relationship:

Where:

To determine the area we will use the formula for the area of a circle:

Where:

Replacing the diameter we get:

Solving the operations we get:

Now we replace it in the formula for the pressure:

Solving the operation:

Therefore, the pressure needed is 159.15 psi.