US Patent 7926157 Hydraulic damper valve

A breakstem rivet placing tool conventionally includes a flow restrictions for hydraulic fluid used to drive the tool in a stem pulling direction. This serves to prevent recoil of the tool due to rapid acceleration of an internal piston when the stem of the breakstem rivet breaks. Prior art flow restrictions create a jet of high velocity hydraulic fluid into the tool which may damage components by erosion. A revised fluid damper valve deflects and/or diffuses the fluid flow to avoid damage by erosion.