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A bonnet assembly for assisting to move a valve stem to a retracted position includes a bonnet body. The bonnet body has a bonnet valve end selectively connected to a valve, a bonnet actuator end opposite the bonnet valve end selectively connected to a valve actuator. A valve stem extends through th

A bonnet assembly for assisting to move a valve stem to a retracted position includes a bonnet body. The bonnet body has a bonnet valve end selectively connected to a valve, a bonnet actuator end opposite the bonnet valve end selectively connected to a valve actuator. A valve stem extends through the central bore of the bonnet body. A booster piston seal circumscribes the valve stem and engages an inner diameter of the central bore. The booster piston seal selectively defines an extent of a pressure cavity containing pressure media. An effective stem pressure surface faces in a direction towards the valve and is in fluid communication with the valve when the bonnet body is connected to the valve. A booster pressure surface faces in a direction towards the valve when the bonnet body is connected to the valve and is selectively acted on by the pressure media.

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1. A bonnet assembly for assisting movement of a valve stem to a retracted position, the bonnet assembly comprising: a bonnet body, the bonnet body having a bonnet valve end selectively connected to a valve, a bonnet actuator end opposite the bonnet valve end selectively connected to a valve actuato

1. A bonnet assembly for assisting movement of a valve stem to a retracted position, the bonnet assembly comprising: a bonnet body, the bonnet body having a bonnet valve end selectively connected to a valve, a bonnet actuator end opposite the bonnet valve end selectively connected to a valve actuator, and a central bore extending along a central axis;the valve stem extending through the central bore, the valve stem having a valve stem valve end selectively connected to a valve member;a booster piston seal circumscribing the valve stem and engaging an inner diameter of the central bore, the booster piston seal selectively defining an extent of a pressure cavity containing pressure media, and a flow of the pressure media into the pressure cavity being blocked by a primary piston seal circumscribing the valve stem until the valve is at an intermediate position between the retracted position and an extended position;an effective stem pressure surface facing in a direction towards the valve and in fluid communication with the valve when the bonnet body is connected to the valve;a booster pressure surface facing in the direction towards the valve when the bonnet body is connected to the valve, the booster pressure surface selectively acted on by the pressure media to drive axial movement of the valve stem; anda pressure media flow path to the booster pressure surface from an outer diameter of the bonnet body. 2. The bonnet assembly according to claim 1, wherein the primary piston seal has a smaller outer diameter than an outer diameter of the booster piston seal. 3. The bonnet assembly according to claim 1, further comprising another pressure media flow path to the booster pressure surface from the bonnet valve end of the bonnet body. 4. The bonnet assembly according to claim 3, wherein the primary piston seal selectively blocks the pressure media flow path to the booster pressure surface from the bonnet valve end of the bonnet body. 5. The bonnet assembly according to claim 1, further comprising an annular recess in the central bore, the annular recess having an inner diameter that is greater than a primary sealing diameter of the primary piston seal circumscribing the valve stem. 6. The bonnet assembly according to claim 1, wherein the booster piston seal is a dynamic piston seal that slidingly sealingly engages the inner diameter of the central bore. 7. The bonnet assembly according to claim 1, wherein the valve stem is moveable between the extended position where the valve stem valve end is farther from the bonnet valve end and the retracted position where the valve stem valve end is closer to the bonnet valve end, and wherein the booster pressure surface is acted on by the pressure media over a selected portion of travel of the valve stem between the extended position and the retracted position. 8. The bonnet assembly according to claim 1, wherein the effective stem pressure surface and the booster pressure surface are both static relative to the valve stem and axially moveable relative to the central bore. 9. The bonnet assembly according to claim 1, wherein the booster pressure surface has a larger surface area selectively acted on by the pressure media than a surface area of the effective stem pressure surface. 10. A bonnet assembly for assisting to move a valve stem to a retracted position, the bonnet assembly comprising: a bonnet body, the bonnet body having a bonnet valve end selectively connected to a valve, a bonnet actuator end opposite the bonnet valve end selectively connected to a valve actuator, and a central bore extending along a central axis;the valve stem extending through the central bore having a valve stem valve end selectively connected to a valve member, the valve stem being moveable between the retracted position where the valve stem valve end is closer to the bonnet valve end and an extended position where the valve stem valve end is farther from the bonnet valve end;a primary piston seal circumscribing the valve stem and having a primary sealing diameter defining an outer diameter of an effective stem pressure surface that faces in a direction towards the valve when the bonnet body is connected to the valve;an annular recess having an inner diameter greater than an inner diameter of the central bore, the annular recess arranged about the valve stem such that the primary piston seal does not contact the inner diameter of the annular recess when the primary piston seal is radially aligned with the annular recess;a booster piston seal circumscribing the valve stem and engaging the inner diameter of the central bore, the booster piston seal having a booster sealing diameter that is larger than the primary sealing diameter of the primary piston seal; and a booster pressure surface facing in the direction towards the valve when the bonnet body is connected to the valve, the booster pressure surface having a larger surface area than a surface area of the effective stem pressure surface. 11. The bonnet assembly according to claim 10, further comprising a pressure media flow path extending to the booster pressure surface from one of the bonnet valve end and an outer diameter of the bonnet body. 12. The bonnet assembly according to claim 10, wherein the primary piston seal is a dynamic seal that slidingly sealingly engages the inner diameter of the central bore. 13. The bonnet assembly according to claim 10, wherein the effective stem pressure surface is in fluid communication with the valve when the bonnet assembly is connected to the valve. 14. The bonnet assembly according to claim 10, wherein the annular recess has the inner diameter that is greater than the primary sealing diameter of the primary piston seal. 15. The bonnet assembly according to claim 10, wherein the booster pressure surface is axially static relative to the valve stem and axially moveable relative to the central bore.