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Simulation Error

Hi,
I was working on a hydraulic circuit. This circuit contains a PRV with opening pressure at 250bars. In this circuit when i start increasing the torque loading at hydraulic motor, the pressure starts building up in the line between the pump and the motor. After a certain limit of torque, the Pressure relief valve, doesnt have any effect on the circuit and the pressure is crossing beyond 250bars, there is no sign of pressure relief, even in the graphs. Does anyone know why this is happeneing? How does PRV stop working?

Pressure drop.png

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English

Twin Activate

v2022.3

Accepted answers

RoKet

Hi Bhuvana Siva Teja,

Can you attach the model? It would be helpful to find the reason for that behaviour.

A reason could be parameterization of PRV. Beside the opening pressure you must choose the correct size of the valve, that means parameters NominalVolumeFlow and NominalPressureDifference. They determine the pressure increase depending on the flow.

All comments

RoKet

Hi Bhuvana Siva Teja,

Can you attach the model? It would be helpful to find the reason for that behaviour.

Bhuvana Siva Teja

Hi RoKet,
Thank you for the support, yes i have attached the model, I gave constant torque loading to the hydraulic motors and Speed input to the Pump. This might help in better understanding the problem.

I've added a few sensors and made some quick tests and manual calculations.

1. Pump with n = 0 (nearly closed end except of leakage)

Pressure according to torque input of motor: M * 2 * pi / (VG * etahm) = 400 bar (per motor)
Opening pressure of PRV = 250 bar
=> rot speed of motors: ~3700 1/min
=> flow: ~1300 l/min
=> pressure drop at PRV: Q / Qnom * dpnom = 1300 l/min / 30 l/min * 5 bar = 206 bar
=> pressure in system: popen + pressure drop = 456 bar

2. Pump with n = 296.3 rad/s

Qpump = 296.2 / (2 * pi) * 60 s * 50 cm³ = 141 l/min
=> pressure in system: 467 bar

Please note that a volume produces volume flow if p < a few mbar (here -1.01325 bar rel).

The torque at motors is way too high for the PRV pressure (or the displacement volume of motors too small).

Bhuvana Siva Teja

Thank you RoKet, for your time and detailed explanation. I understood the problem and ways to tune the model.

Actually i was trying to simulate using the maximum torque it can reach under 250Bars, that was a mistake. I should be using starting torque which is way less. That actually matches the conclusion you gave. Thank you