Advanced Engine Valve Quality Testing

A Resonic acoustic resonance engine valve scanner is a gateway to product quality information at production speeds that has been previously unfeasible until now. It offers manufacturers of engine valves and other automotive engine components a combination of full component test coverage, better defect resolution, a faster test, and a smaller equipment footprint.

Component Specifications

  • Valve Materials: martensitic steels, austenitic steels, super alloys, titanium alloys
  • Stem diameters: 2mm up to 0.75 inches
  • Stem lengths: up to 24 inches
  • Stem constructions: solid, bi-metallic, hollow-stem, sodium-filled


diagram of local resonance field in stem NDT scan High frequency resonances are generated in small, bounded areas of a valve stem or valve head and the EMAT probes are automatically and continuously moved along the length of the valve. The resonance properties extracted during the valve scan are analyzed for the component's material elasticity and response to acousto-mechanical stresses which are the pathway to detection of a variety of defect types. By evaluating small areas in isolation using resonance, it is possible to create a very low noise and high sensitivity test compared to UT, eddy current, and full body acoustic methods traditionally used for in-line valve inspection.

Test Process

A typical automotive engine valve stem can be evaluated for a range of manufacturing or material defects in under 2.5 seconds using 100 test points per inch of vertical stem length. In a separate 1-2 second scan with alternatively positioned EMAT sensors, the valve head can be tested with similar data density and one turn of rotational motion.

Laboratory valve scannerValves are loaded manually or automatically into a chuck and the scan of either the valve head or stem proceeds automatically under the control of ARIS system software.

Given a predetermined set of electrical and software test settings, resonance amplitude and frequency data is sampled at high speed along the length of the valve stem or over the rotation of a valve head to produce a unique valve profile. Individual profiles from valves of the same type are typically very similar since they are acoustically imprinted with traits of the manufacturing processes used to produce them. The system uses a modest number of profiles from known good valve samples to set rejection criteria for subsequently tested defective valves.

Full Stem Test Capabilities

  • Ultra small straightening cracks
  • Surface breaking and sub-surface friction weld defects
  • Hollow stem ID defects, wall thickness, and concentricity
  • Over and under-hardened valve stem tips
  • Nitride or hard chrome coating defects
  • Heat and age related grain growth

Valve Head Test Capabilities

  • Valve fillet and head forge laps
  • Combustion face cracks
  • Valve seat deposition porosity and bond quality


Video Demonstration of the ARIS Valve Scanner


  • 3700 Series ARIS Signal Processing Unit
  • Computer keyboard
  • Minimum one pair of Bulk-wave Pencil Probe EMAT sensors
  • Wear inserts and bushings for each nominal valve stem size to be tested
  • Motion controlled valve scanning lab fixture or integrated, in-line valve handling machine

Additional Resources

Valve stem inspection technology presentation slides (pdf) 01/2013
Application report: Detection of Valve Seat Porosity
Application report: Detection of Forge Defects on Valve Fillet
Application report: Detection of Forge Defects on Valve Head
Application report: Measurement of Valve Stem Grain Growth