Tri State Hydraulics


Epoxy is used as an alternative to brazing when joining the feedback mechanism ball and wire.  This is widely used when joining sapphire to a stainless steel wire.  Sapphire cannot be brazed to stainless steel, so the only alternative bonding technique is epoxy.  In perfect conditions, the epoxy is an equally viable manufacturing technique, however in the servo valve applications there are other factors that can cause unexpected failure.  Most importantly, the chemicals in the hydraulic fluids can cause deterioration of the epoxy and there are indications that the epoxy breaks down even within the normal operating temperatures between 0 degrees F/-17.7 degrees C to 160 degrees F/71 degrees C.

The manufacturing process of the feedback mechanism is a major consideration when elaluating a servo valve. Specifically, the use of epoxy as joining technique may in fact be comparable to brazing in an ideal case.  That is to say, ideal being that cleanliness of the hydraulic fluid is maintained in a pristine or controlled condition.  Secondly, the concern with regard to temperature susceptibility of the epoxy shouldn't be a risk that you need to take.  In comparison, there are no known issues related to the bond created between stainless steel and the carbide ball using brazing.

PUMPS, VALVES & MOTORS MOOG Valves Design of Long Life... 8 Techniques Ensuring... Epoxy