View the Newsletter

A widely studied problem in the fluid mechanics literature is water hammer. Rapid closure of valves causes pressure surges upstream of the valve, which can be very damaging to piping systems and piping supports. For PRV’s chattering in liquid service, a similar problem occurs when the PRV closes rapidly. Data reported by the American Petroleum Institute (API) on incidents involving PRVs in liquid service support this assertion. Water hammer is manifested as a series of shocks, sounding like hammer strikes, which may have sufficient magnitude to rupture pipes or damage connected equipment. The excess pressure due to water hammer is additive to the normal flow pressure in the pipe.

The coupled solution of fluid hydraulics and timed valve closure is very similar to the PRV stability analysis in liquid service. Instead of the valves closing over a specified time, the PRV will close and open based on a force balance around the valve disk. Since liquid flows are rarely choked, the PRV stability solution is simpler than choked gas and/or multiphase flow.

Read this newsletter by Georges Melhem, Ph.D., FAIChE, for a methodology to solve the timed valve closure and the pressure relief valve (PRV) stability problems. There are a lot of similarities and essentially the same boundary conditions for the inlet line. Topics include:

• Introduction
• Liquid Pressure at Closing Valve
• Singh and Shak Estimate of Δ P total 
• SuperChems^® Expert Solution

Bonus!
This newsletter also includes access to the 46-minute presentation by Georges Melhem, Ph.D., FAIChE, to learn practical methods for the identification and evaluation of high risk relief systems installations. He will demonstrate advanced developments in PRV stability and include working examples on evaluating and performing engineering analysis when PRV instability is suspected using Process Safety Office^® SuperChems^® software.

Have a great and safe day.

View the Newsletter