Safety relief valve

An improved safety relief valve including a hollow valve body having a fluid inlet, a fluid outlet, a valve seat encircling said inlet, a valve member movable toward and away from said seat defining a cracking area when in engagement with said seat, adjustable means biasing said valve member into sealing engagement with said seat until the fluid pressure in said inlet exceeds a predetermined value, and a valve member carrier having a downwardly projecting peripheral flange having a lower end and providing a cylindrical interior, the improvement comprising orifice forming means on said valve seat, said orifice forming means including:

• an annular member moveably located on said seat;
• a cylindrical outer peripheral surface on said annular member sized to fit closely and concentrically within the cylindrical interior of the flange of said valve member carrier and always disposed within the lower end of said flange when said valve member is in engagement with said seat forming a substantially constant area, variable length orifice therewith when said valve member is in engagement with or relatively close to said seat defining a lift area that is substantially larger than said cracking area;
• a radiused end surface on said outer peripheral surface forming a variable area orifice with the end of said flange when said valve member is located remote from said seat, whereby a large volume flow area change occurs upon slight movement of said valve member relative to said orifice forming means;
• an axially projecting annular portion smaller in diameter than said outer peripheral surface extending toward said valve member and forming a second orifice with said valve carrier member defining a closing area of a size between said cracking area and said lift area;
• and,
• a locking member extending into said valve body and engaging said annular member for permitting and preventing rotation of said annular member on said seat.