For a Liquid-level control system similar to that in figure, Appelpolscher has argued that integral control action

Question:

For a Liquid-level control system similar to that in figure, Appelpolscher has argued that integral control action is not required because the process acts as an Integrator (cf, Eq. 11-77). To evaluate his assertion, determine whether proportional-only Control will eliminate offset for step changes in
(a) Set point and
(b) Disturbance variable.