A fast valve action or pump disturbance can launch a pressure wave in the cooling-water circuit. Its peak at the cooler depends on pipe length, wave speed, valve motion and reflections. The normal pump discharge pressure does not define this transient duty. [1]
Start with the event time scale
For a simple line, compare valve action time with round-trip wave time 2ℓ/a, where ℓ is pipe length in metres and wave speed a is m/s. A rapid velocity change can be screened with Δp ≈ ρaΔu, using water density in kg/m³ and velocity change in m/s to obtain pascals.
This Joukowsky-type screening assumes the relevant rapid change and a simple liquid-filled line. It does not include cavitation, air pockets, complex branches or arbitrary valve closure profiles. It is a scale estimate, not a permitted closure time.
Write the boundaries that return the wave
| Boundary | Data retained | Potential effect |
|---|---|---|
| Isolation valve | Position-versus-time and actual flow characteristic | Launched pressure change |
| Tank or reservoir | Connection and head | Reflection and pressure reference |
| Pump/check valve | Trip and closure behavior | Additional transient source |
| Cooler/branch junction | Hydraulic geometry and compliance | Local peaks and flow redistribution |
Maintenance guidance identifies faulty valve position, pump rotation and obstructed cooling paths as conditions worth recording [2]. Establish the actual initial valve and pump states before assigning the event that launches the pressure wave.
Screen the rapid-closure pressure scale
Assume a liquid-filled straight line with density 1,000 kg/m³, wave speed 1,000 m/s and rapid velocity reduction of 1 m/s. The ideal pressure increment ρaΔv is 1 MPa. For assumed 50 m line length, round-trip wave time is 0.10 s. Evaluate actual valve motion and reflections against component limits; these scales are not operating permissions.
For an additional assumed 0.02 s rapid stop and 0.30 MPa gauge initial local pressure, the ideal first-wave scale is 1.30 MPa gauge. It exceeds an assumed 1.00 MPa gauge component review limit. Escalate the transient model and closure design; this comparison does not establish reflected-wave maxima or a permitted valve setting.
Check maximum and minimum pressure
Evaluate pressure throughout the event at the cooler, including low-pressure periods and rebound. A high peak can challenge mechanical design; a sufficiently low pressure can change the hydraulic regime and invalidate a single-phase model.
References
- U.S. Department of Energy, DOE-HDBK-1012/3-92, Thermodynamics, Heat Transfer, and Fluid Flow, Volume 3, 1992.
- U.S. Bureau of Reclamation, FIST Volume 3-30, Transformer Maintenance, 2000.