Fluid pressure activated firing head for providing clean fluid

Claim 1

In a fluid pressure actuated perforating gun suspendable on a well conduit by a packer having a central bore, said packer central bore being of greater diameter than said well conduit bore, said gun being supported by a tubing assembly depending from the packer and having an axially extending fluid passage connected to a fluid pressure actuated firing mechanism adjacent the perforating gun, the improvement comprising: a sleeve mounted in said packer central bore and having a bore substantially equal in diameter to said conduit bore and in communication with said well conduit bore, said sleeve defining an annular fluid passage extending upwardly through the packer and terminating at its upper end in an annular downwardly directed passage communicating with the well annulus above the packer; pressure transmitting sealing means fixedly secured in the lower end of said downwardly directed passage; conduit means communicating between said annular fluid passage and the axially extending passage of said tubing assembly, whereby the axially extending fluid passage of said tubing assembly and said conduit means may be filled with a first fluid at the top of the well and such that fluid remains uncontaminated by well fluids during insertion and residence in the well.