Early Butterfly Valve Testing with Incompressible Flow

Kalsi Engineering (KEI) conducted a water flow test program for butterfly valves for the nuclear industry as part of the EPRI Performance Prediction Methodology (PPM) between 1993 and 1994. The EPRI PPM program included model development for gate, globe, and butterfly valves. The water flow loop test program included scaling validation by comparing the predictions based upon KEI flow loop testing of a precisely scaled 6-inch model to  a 42-inch single offset design. The 42-inch valve was tested at the Utah Water Research Laboratory (UWRL) at Utah State University. The early technology developed by KEI was used in the ERPI PPM software (read more about EPRI PPM here).

KEI started a self-funded water flow loop test program to expand the library of hydrodynamic torque coefficients for butterfly valves in 1999. The hydrodynamic torque coefficients and related technology developed from this test program were built upon KEI’s earlier efforts on the EPRI program. The KEI test program included systematic evaluation of a wide matrix of disc shapes, disc aspect ratios (disc thickness to disc diameter), elbow orientations and proximities, and flow rates. The disc designs were selected based upon an industry survey. The test matrix included 1,272 incompressible flow tests which by far is the largest test database in the nuclear power industry.

Industry Leaders in Compressible Flow Testing of Quarter-turn Valves

Based on KEI’s commitment to the nuclear power industry, KEI initiated a self-funded compressible flow test program in 2002 to develop aerodynamic torque coefficients for butterfly valves and other quarter-turn valves.

The KEI compressible flow test program was preceded by a Nuclear Regulatory Commission (NRC) funded program conducted by Idaho National Engineering Laboratory (INEL) in the 1980s. The NRC program included three test specimens. Two of the specimens had geometric designs with common features. Although the study was limited in the number of disc designs/geometries and in number of piping configurations used, the test program provided valuable insights into the different nature for aerodynamic torque and hydrodynamic torque.

Prior to the NRC program, it was believed that both shaft upstream and downstream orientations produced self-closing hydro/aerodynamic torque. The NRC test program revealed that aerodynamic torque was in fact self-opening for the shaft downstream orientation for the disc designs and under the operating conditions tested. This was a significant finding as valve and actuator assemblies used in containment purge applications up to that time were sized based on the belief aerodynamic torque was largely self-closing.

KEI’s compressible flow test program was no small effort whether measured in dollars or manpower. The KEI compressible flow test program included a wide selection of disc designs, piping configurations and operating pressures and included 1,116 compressible flow tests. The KEI test program revealed that the direction of the aerodynamic torque (i.e., whether it was self-opening or closing) was primarily dependent on two key factors: (1) the disc aspect ratio and (2) the pressure ratio across the valve (ratio of downstream pressure to upstream pressure using absolute pressure units). Highlights of the compressible flow test program are provided in the movie below.

The difference in torque direction due to aerodynamic and hydrodynamic forces results from the difference between the incompressible flow field and the flow field composed of transonic and supersonic regions  attached to and surrounding the downstream disc. The flow field in the movie below shows supersonic and transonic flow in the flow field region downstream of a disc. The movie starts with the valve under no-flow conditions. A few seconds into the video, a fast-acting ball valve, located upstream of the test specimen, opens and the roar of discharged gas is heard. Condensation around the disc forms due to the substantial decrease in local pressure and temperature associated with the supersonic flow and expansion waves which are present downstream of the disc. The flow field changes as the disc closes.

The flow just downstream of the disc when surrounded by pipe can achieve supersonic velocities greater than a Mach number of 3. The high velocity is possible due to the converging-diverging flow regions formed by the disc and pipe walls when the disc is approximately 45 degrees open.

Culmination of Decades of Work

KVAP is the industry leading valve and actuator analysis software.  KVAP was developed and refined using the data gained from this several-decades long flow test program. KVAP, and its underlying technology, is used by many US and international nuclear power plants to calculate operating margin under design basis conditions and ensure plant safety and reliability. You can read more about KVAP here: https://www.kalsi.com/sites/default/files/literature/kvap_brochure.pdf

Contact Kalsi Engineering to learn how KVAP can increase the reliability and safety of your plant or to find out how KEI laboratory services can help determine the performance and reliability of your equipment.