Drop-bar hydrostatic firing head
The drop-bar hydrostatic firing (BHF) head is bar activated and hydrostatically fired. The BHF head consists of a downhole fill sub with a no-go guide firing head that has an internal firing pin and a drop bar. When the drop bar hits the release sleeve, it shears the retaining shear ring that secures the release mechanism and shifts the sleeve down. This movement releases the balls holding the firing pin. When the firing pin is freed, hydrostatic pressure propels the pin into the percussion detonator. Hardware is available to prevent trapped pressure, and its use is recommended.
The drop bar is equipped with an upper fishing neck, lower extension nose, and brass impression block (telltale). Circular grooves on the top of the release sleeve leave a recognizable pattern on the brass nose telltale of the drop bar. Additional 1.524-m [5-ft] extension weights can be added for deviated well applications. A one-piece drop bar is also available for upset tubing or significant changes in tubing ID. In dry pipe, the drop bar is always run on slickline.