Water level difference by pumping Open tank is partially filled with water and is divided into two equal parts by the wall. The wall has pipe that connects both sections. Obviously, water levels are equal from both sides (Fig.1).
Then, water is pumped from right section of the tank to the left one with constant flow rate (Fig.2).
Q1: Is it possible to calculate the difference in water levels knowing all values (volume, flow rate, pump capacity, etc.)?
Q2: How the water levels difference will change if the tank will double its size (Fig.3)? Or it will be the same?

 A: Once the water levels stabilize, Flow rate through the pump equals flow rate through the link pipe. Effectively the problem is identical to pumping water from one infinite source to another infinite source x distance higher through a similar dimensioned pipe. Therefore the sizes of the tanks do not affect the water level height difference. 
The solution to Q1 comes down to finding the pressure difference at both sides of the link pipe. If flow rate is known then pressure drop can be obtained based on known pressure/flow rate curve (specific to that pump, and empirical in nature). This pressure drop is equal to the pressure exerted by the water column above the reference level. Divide this pressure by water density and gravitational field strength g to get water height. 
A: For Q1, what @gregsan said, plus it depends on the nature of the orifice flow. As a first approximation, for slow flow rate (viscous) the pressure is linear in the flow rate.
For fast flow, the pressure is quadratic.
So the flow rate vs. pressure response of the orifice is the most difficult thing to quantify theoretically, and should be established through experimentation or some simple calculator.
For Q2, the steady-state between Figure 2 and Figure 3 will be the same, but in Figure 3 it will take longer to reach the steady-state.
