Low pressure pneumatic and gate actuator

A pneumatic actuator for depressurizing a piston reciprocable within a cylinder, said actuator comprising:

• a first chamber having a flexible first diaphragm mounted therein and sealingly dividing said first chamber into first and second chamber portions, both said chamber portions being in fluid communication with said cylinder, said second chamber portion having an opening providing fluid communication with the ambient and surrounded by a seat facing said first diaphragm, said first diaphragm being deflectable into sealing engagement with said seat to seal said opening when said cylinder is charged with a fluid;
• a second chamber having a flexible second diaphragm mounted therein and sealingly dividing said second chamber into third and fourth chamber portions, said third chamber portion being in fluid communication with a source of compressed fluid, said fourth chamber portion being in fluid communication with the ambient and having an aperture providing fluid communication with said first chamber portion, said aperture being surrounded by a second seat facing said second diaphragm, said second diaphragm being deflectable into sealing engagement with said second seat to seal said aperture when said third chamber portion is charged with a compressed fluid;
• and
• a third chamber having a flexible third diaphragm mounted therein and sealingly dividing said third chamber into fifth and sixth chamber portions, said fifth chamber portion being in fluid communication with a second source of compressed fluid, an elongated plunger having one end positioned within said sixth chamber portion and engagable with said third diaphragm, the other end of said plunger being positioned within said third chamber portion and engagable with said second diaphragm, said third diaphragm being deflectable into engagement with said one end of said plunger when said fifth chamber portion is charged with a compressed fluid, said plunger being thereupon forced into engagement with said second diaphragm and thereby forcing said second diaphragm into sealing engagement with said second seat, said second diaphragm being deflected out of engagement with said second seat only when both said fifth and said third chamber portions are vented to lower the fluid pressure in each said third and fifth chamber portions to a predetermined value, fluid in said first chamber portion being permitted to enter said fourth chamber portion and exit to the ambient, thereby allowing said first diaphragm to deflect out of engagement with said first seat and allowing fluid to flow from said cylinder through said second chamber portion and exit to the ambient thereby depressurizing said piston and allowing it to move within said cylinder.