Pressure relief valves are the last line of defense in the overpressure protection of idustrial processes. If they fail to vent properly (either due to incorrect sizing or due to valve chatter), the protected vessel is likely to explode.

These valves -- expecially the direct spring operated ones -- are extremely simple mechanical systems. Still, they exhibit surprisingly complex behaviour!

Computation fluid dynamics (CFD)

The dynamics of the valve can be computed by means of CFD (Computational Fluid Dynamics). This typically requires computationally extensive simulations, not only for the valve itself but also of the upstream and downstream piping. Having said that, this is the most accurate way of valve modelling!

Reduced order modelling (ROM)

Unsteady 1D pipeline dynamics coupled with 1 DoF (degree-of-freedom) valve models can perform surprisingly good. The figure on the left shows the valve lift and pressure time histories computed by ROM (black) and CFD (red). Can you guess the factor of computational efforts?

The four shades of valve chatter

"Valve chatter" and "valve flutter" refer to unstable vibration of valves. However, there are several physical mechanisms behind valve oscillations...

Oversized valve

Pressure relief valves venting only a small portion of their capacity flow rate will go unstable. Solution: use a smaller and a larger valve connected in tandem and adjust the set pressure of the larger one slightly higher.

Helmholtz instability

If upstream piping (between the vessel and the valve) is present, they form a Helmholtz resonator. The valve mechanical eigenfrequency must be higher than that of the Helmholtz resonator (pipe+reservoir).

Quarter-wave instability

In this case, the first acoustic mode of the upstream piping excites the valve. There is no easy way of suppressing this instability, but have a look at our papers to find out more!

Small flow + blowdown = cycling

Imagine that the valve closes at a lower pressure than the opening pressure (that is, the blowdown of the valve). If such a valve vents small flow rates, it will start "cycling", that is open, vent some fluid and the close and stay shut until the vessel pressure reaches the set pressure again.

Selected papers

Interested? Have a look at our recent papers!

  • Journal papers

    • Erdődi, I ; Hős, C: Prediction of quarter-wave instability in direct spring operated pressure relief valves with upstream piping by means of CFD and reduced order modelling JOURNAL OF FLUIDS AND STRUCTURES 73 pp. 37-52. , 16 p. (2017)

    • Hos, CJ ; Champneys, AR ; Paul, K ; McNeely, M: Dynamic behaviour of direct spring loaded pressure relief valves connected to inlet piping: IV review and recommendations JOURNAL OF LOSS PREVENTION IN THE PROCESS INDUSTRIES 48 pp. 270-288. , 19 p. (2017)

    • Erdődi, István Tamás ; Hős, Csaba : Numerical modelling of a direct spring operated pressure relief valve JOURNAL OF COMPUTATIONAL AND APPLIED MECHANICS 11 : 2 pp. 123-136. , 14 p. (2016)

    • Hos, CJ ; Champneys, AR ; Paul, K ; McNeely, M: Dynamic behaviour of direct spring loaded pressure relief valves: III valves in liquid service JOURNAL OF LOSS PREVENTION IN THE PROCESS INDUSTRIES 43 pp. 1-9. , 9 p. (2016)

  • Conference papers

    • Erdődi, István Tamás ; Hős, Csaba ; Felhős, Dávid: Stability analysis of spring operated check valves with upstream and downstream pipings In: Vad, J (szerk.) Proceedings of Conference on Modelling Fluid Flow (CMFF'18) : 17th event of the International Conference Series on Fluid Flow Technologies Budapest, Magyarország : CFD.HU Kft., (2018) Paper: Paper 56 , 8 p.

    • Erdődi, István ; Hős, Csaba: Effect of Disc Geometry on the Dynamic Stability of Direct Spring Operated Pressure Relief Valves In: M., Papadrakakis; V., Papadopoulos; G., Stefanou; V., Plevris (szerk.) ECCOMAS Congress 2016 : Proceedings of the VII European Congress on Computational Methods in Applied Sciences and Engineering Hersonissos, Greece: European Community on Computational Methods in Applied Sciences (ECCOMAS), (2016) pp. 7695-7702. Paper: 10824 , 8 p.


Feel free to contact us!

  • Address

    Dept. of Hydrodynamic Systems, Budapest University of Technology and Economics, 1111 Budapest, Muegyetem rkp. 3
  • Email

    Csaba Hős
  • Phone

    (+36) 1 463-2216