I can't provide both pressure and flow input at the same time in the hydraulic system

I created an isothermal model with Simscape, but I couldn't operate my hydraulic pump at 200 bar system pressure and 30 L/min flow rate. I defined the pressure as 200 bar using the pressure source block and limited the flow rate with an orifice, but this time the orifice diameter comes out to be very small. How can I operate the system at the desired pressure and flow rate?

[Sam Chak]

Hi @ali kaya

This appears to be a physics problem involving pressure regulation, described as an engineering application of a hydraulic pump. Most physics problems that describe how a quantity changes over time can generally be expressed using a differential equation, , where q represents the physical quantity, such as length, mass, electric current, pressure, temperature, amount of substance, and luminous intensity.

First, did you construct the Simscape model strictly according to the pressure differential equation that you derived for the hydraulic system? Avoid constructing the Simscape blocks based solely on intuition or assumptions. It is essential to ensure that each Simscape block behaves exactly as the mathematical model you derived in your paper. However, it is worth noting that the behaviors of certain Simscape blocks can sometimes be too "realistic," which may be overlooked in the textbook-style mathematical modeling process.

Secondly, have you mathematically verified from the differential equation that the pressure at steady state remains at 200 bar? If the mathematical analysis indicates that the steady-state pressure is not at 200 bar, this may imply that the pressure control scheme in the hydraulic system is incorrectly designed. Conversely, if it is at 200 bar but the desired pressure cannot be achieved in the Simscape simulation, then it is likely that the Simscape model is incorrect.

[Dyuman Joshi]

@Sam - I highly doubt that hydraulic system would follow a differential equation, given that it could have multiplte elements with different pressure requirements, which are not necessarily time-based/defined.

Which means, that is might not be steady state pressure, but most likely the pressure required to overcome the resistance or in other words - the working output of the pump.

@ali kaya - It would be better if you could provide more details as to what you are trying to do/achieve/solve. Why do you need orifice? Is it working as a pilot to operate a PRV or other control object? Is there any actuator in the system? What does the pump provide energy for?

[Sam Chak]

Hi @Dyuman Joshi

I agree. A practical hydraulic system does not strictly follow a differential equation due to nonlinearities, unmodeled dynamics, noise, and parameter uncertainty. However, it is often a good starting point in early design for the OP to construct the system using engineering calculations, mathematical models, and documented assumptions that satisfy operating conditions, safety margins, and industrial codes and standards. Of course, it is also possible for the OP to build a simple system in Simscape entirely based on his experienced engineering judgment.

Nevertheless, having a robust mathematical model is usually beneficial for troubleshooting in Simulink, as it allows the OP to compare simulated component behavior against the equations to identify the source of deviations. More importantly, mathematical models reveal internal balances and state variables that can be conveniently investigated to find mismatches. Fortunately, most Simscape blocks provide the mathematical models in their documentation.

[ali kaya]

Pressure (Pa) Flow Rate (m³/s) Fixed Displacement Pump Hydraulic model

I placed pressure and flow sensors immediately after the pump to check the values I input to the pump, but the sensors did not confirm the values I entered.

[Sam Chak]

Hi @ali kaya

Without the pressure dynamical model and your verification, I cannot tell what went wrong from the graphical Simscape-styled piping and instrumentation diagram from an engineering perspective, particularly since the names of the important blocks are hidden. Perhaps @Dyuman Joshi can offer some advice.

Answer 1

[ali kaya]

I forgot to add a pressure relief valve to the system, which is why the pressure was getting too high. After adding the pressure relief valve, the issue was resolved.

[Dyuman Joshi]

I thought the issue was with Pressure not being delivered.

Nevertheless, good to know that the issue is resolved.