Pressure-balanced well service valve

Claim 1

An underground wellbore treating valve assembly for the injection of predetermined quantities of fluids into low pressure downhole formations, said valve assembly comprising: an elongated tubular housing having a central bore passage therethrough and adapted for sealing engagement in a conduit string; an annular valve seat formed in the wall of said housing in said bore passage; an inner annular shoulder formed in said housing below said valve seat; seal means in said annular shoulder; a sliding valve member closely fitting in said annular shoulder and having a valve-seat-closing upper portion arranged for sealing engagement with said valve seat; upward biasing means located below said valve member and in abutment therewith; bottom abutment means below said biasing means, in abutment therewith, and arranged to retain said biasing means in said housing; a first pressure response area on top of said valve member and exposed to said valve seat; a second pressure response area on said valve member below said annular shoulder and of less cross-sectional area than said first pressure response area; port means through the wall of said housing between said valve seat and said annular shoulder; and, a pressure bypass passage communicating from above said valve seat to below said annular shoulder.