# Limit charge of electronic–hydraulic analogy of a compartment

I am doing a mathematical model of an hydraulic system and I am using an electronic-hydraulic analogy. Normally a compartment is simulated with a capacitor.

But in my system I can apply a big pressure (Input voltage) at the entrance of the model, and because we are using an ideal capacitor, the charge of the capacitor (the volume of this compartment) can always increase if the input voltage increase. But in reality, this compartment has a maximum volume, and normally, if this maximum volume is reached, the compartment is going to put some opposition to this pressure.

So I have some ideas of how to represent this, but I wanna know if there is any formal representation or an existent model.

• The capacitor is going to have to be non-linear. – Chet Miller Jul 3 '18 at 19:26

## 1 Answer

As the level of fluid in the compartment is increasing, so will the pressure at the bottom. So, if you fill the compartment from the bottom, at some point, the pressure at the bottom will equalize the maximum output pressure of the pump and oppose the flow.

The area (horizontal cross-section) of the compartment is an analog of the capacitance, i.e., for any given fluid level (height of the column or bottom pressure), the compartment with a greater area will hold a proportionally greater volume of fluid (analog of charge).

$Q=CV(voltage)$ would be analogous to $V(volume)=Ah$