Tri State Hydraulics

6 Ball-in-Hole...

...Technology Increases Life Expectancy

In terms of servo valve reliability, the sapphire and carbide ball are comparable.  Both are excellent choices strictly from an endurance perspective (based on test results shown in the previous section).  The other factor to take into consideration is the method used to couple the feedback mechanism ball to the spool.  Moog conducted extensive research and development on the servo valve to extend the lifetime of the feedback mechanism and spool. By 1998, further innovations were introduced with development of the carbide ball-in-hole technology.  The materials remained the same, however a spherical seat is machined into the spool to the precise dimensions of the ball.  

Figure 6 - "Ball-in-Hole" Technology:  Carbide ball extending through the hole in the spool

The manufacturing operation used to make the hole in the spool is referred to as "ballizing."  "Ballizing" creates a hardened surface in the spool that exceeds the capability of heat treatment.  The surface area of the carbide ball in contact with the spool is increased to reduce concentrated contact at any one point on the surfaces.  Thus, it is a combination of mechanical design and a novel manufacturing process that radically improved the life expectancy of the servo valve.  The "ball-in-hole" technology has now replaced the slot cut into the spool.  It did not take long before design engineers recognized the superiority of the carbide "ball-in-hole" technology and they began to demand this for all new applications. Since, 1998, the use of a carbide ball has remained state of the art, however new manufacturing techniques have been identified that extend the life of the feedback mechanism even further.  Today over 95% of all Moog's MFB Servo Valves have been converted to "ball-in-hole" technology and the remaining are specialized valves waiting for international certifications.


Today 95% of all Moog MFB Servo Valves have been converted to ball-in-hole technology.

PUMPS, VALVES & MOTORS MOOG Valves Design of Long Life... 6 Ball-in-Hole...