Retrievable Bridge Plugs are lowered down hole to the desired setting depth at which point the drill string can be filled with water and pressurised to inflate the packer.
An overpull is then applied to the work string to confirm packer inflation, once satisfied with seating anchor a larger overpull is applied to shear designated pins at a pre-determined load.
The retrievable aspect is typically common for temporary isolation or to assist in well integrity testing.
For retrieval a latching sub is run in and located within the plug, an over pull is then applied to shear pins to deflate the packer. Once deflated the plug is retrieved via the latching sub.