A plug valve adapted for controlling flow through high-pressure fluid flow lines, said plug valve comprising:
- (a) a housing adapted for assembly into a high-pressure flow line, said housing comprising:
- i) first and second conduits;
- ii) a generally cylindrical valve stem passage;
- iii) a generally cylindrical access bore having a diameter;
- and
- iv) a generally cylindrical chamber, said chamber:
- (1) communicating with said first and second conduits, said housing valve stem passage, and said access bore;
- said chamber:
- (2) being generally aligned axially with said housing valve stem passage and said access bore;
- and
- (3) having a diameter greater than said diameter of said access bore, thereby providing an annular undercut in said chamber;
- (b) a cap threaded into said access bore, said cap having:
- i) a valve stem passage;
- and
- ii) a main seal ring mounted between said cap and said access bore, said main seal ring having a diameter less that said diameter of said chamber;
- (c) first and second seat inserts, each said seat insert:
- i) having the general shape of a lateral segment of an open cylinder;
- ii) having a transverse passage;
- and
- iii) being mounted in said undercut of said chamber such that said transverse passage of said first seat insert aligns with said first conduit and said transverse passage of said second seat insert aligns with said second conduit;
- (d) a valve body, said valve body:
- i) being mounted in said housing valve stem passage, said chamber, and said cap valve stem passage for rotation about a primary axis;
- ii) having a generally cylindrical midsection, said midsection:
- (1) being adapted to seat on said seat inserts;
- (2) having an upper annular surface and a lower annular surface;
- and
- (3) having a passage extending axially through said midsection from said upper annular surface to said lower annular surface, said passage allowing equalization of fluid pressure above and below said midsection;
- (4) wherein said upper annular surface of said valve body and said lower annular surface of said valve body have substantially equal surface areas;
- iii) having an upper valve stem extending through said housing valve stem passage;
- iv) having a lower valve stem extending through said cap valve stem passage;
- v) a first plug seal ring mounted between said upper valve stem and said housing valve stein passage and having a diameter;
- and
- vi) a second plug seal ring mounted between said lower valve stem and said cap valve stem passage and, having a diameter substantially equal to said diameter of said first plug seal ring;
- and
- vii) having a flow port through said midsection;
- wherein said flow port:
- (1) aligns with said seat insert passages and said conduits to allow flow through said valve when said valve body is rotated to an open position;
- and
- (2) is out of alignment with said seat insert passages and said conduits to shut off flow through said valve when said valve body is rotated to a closed position.