Low pressure actuator for dry sprinkler system

A low pressure actuator for use in a dry, low-pressure, pressurized-gas, fire control and suppression sprinkler system for providing a pressurized fire extinguishing liquid, wherein there is a system gas pressure of not more than about 20 psi and an extinguishing liquid supply pressure of up to about 300 psi, regardless of system gas pressure, whereby the low pressure actuator is actuated by allowing liquid to flow through the low pressure actuator to a sprinkler check valve, when the system air pressure falls to a predetermined pressure, to thereby, in turn, actuate the sprinkler check valve to provide a fire extinguishing liquid flow for distribution through a piping system to a plurality of interconnected sprinklers, the low pressure actuator comprising:

• a.) a housing having a gas compartment and a liquid compartment therein, each of the gas and liquid compartments having an inlet and an outlet for the respective inflow and outflow of a pressurized gas and a pressurized fire extinguishing liquid;
• b.) means for initially pressurizing the gas compartment;
• c.) a first diaphragm, acting as a gas-liquid barrier, the first diaphragm being flexible and moveable, and having a surface area, such that a first, gas-side of the diaphragm is in fluid communication with gas in the gas compartment and a second, liquid-side of the diaphragm is in fluid communication with the liquid;
• d.) a second diaphragm, acting as a water flow barrier, the second diaphragm being flexible and moveable, and having a surface area, such that when the low pressure actuator is in a closed, ready-condition, a first side of the second diaphragm is in a wet state, in fluid communication with the liquid, and a second side of the second diaphragm is in a dry state, in communication with the liquid outlet;
• and when the low pressure actuator is in an actuated condition, both sides of the second diaphragm are in a wet state, in fluid communication with the liquid;
• and
• e.) a connecting passage between the liquid side of the first diaphragm and the liquid compartment such that when gas pressure in the sprinkler system in which the low pressure actuator is placed drops below a pre-determined set point, after an initial pressurization of the sprinkler system and the low pressure actuator, to a pressure above the set point, a pressure equilibrium on the first diaphragm is upset causing the first diaphragm to move and allow a priming flow of liquid to the liquid outlet through a liquid by-pass, which is otherwise sealed when the first diaphragm is in a gas-liquid pressure equilibrium condition, thereby also simultaneously causing the second diaphragm to move and allow a greater flow of liquid to provide the main extinguishing liquid through to the liquid outlet.

A low pressure actuator (1), for use in a dry, pressurized-gas, water sprinkler system, the low pressure actuator (1) comprising:

• a.) a main housing (2), having a vertical axis, and including an upper chamber (3), a middle chamber (4), and a lower chamber (5), the chambers being spaced along the vertical axis, such that the upper chamber (3) and the middle chamber (4) are in communication with one another, and the middle chamber (4) and the lower chamber (5) are in communication with one another;
• b.) the upper chamber (3) further including an interior gas compartment (6), for accumulation of a volume of pressurized gas, and a gas inlet orifice (7), for inlet of a pressurized gas therethrough and into the interior gas compartment (6), from a pressurized gas supply source located exterior to the low pressure actuator, the gas inlet orifice (7) being in sealable fluid communication, at a first end thereof, with the pressurized gas supply source, and in fluid communication, at a second end thereof, with the interior gas compartment (6);
• c.) a tripping device (8), in communication with the upper chamber (3), the tripping device (8) having a tripping device housing (9) containing a tripping device gas compartment (10), such that the tripping device gas compartment (10) is in fluid communication with the gas compartment (6) of the upper chamber (3), the tripping device housing (9) further having a gas passageway (11) therethrough, leading from the tripping device gas compartment (10) to the tripping device gas outlet orifice (12);
• a tripping device gas piston (13), positioned in the tripping device gas passageway (11), the gas piston (13) being alternatively slidable between a closed position, wherein a gas-pressurized condition is established in the tripping device gas compartment (10) and the interior gas compartment (6) of the upper chamber (3), with the gas piston (13) forming a fluid-tight seal between the tripping device gas compartment (10) and the tripping device gas outlet orifice (12);
• and an open position, wherein gas pressure in the gas compartment (6) of the upper chamber (3) and the tripping device gas compartment (10) is relieved and gas is allowed to flow out from the gas compartment (6) and the tripping device gas compartment (10), through the passageway (11), and out through the gas outlet orifice (12);
• a mechanical compression spring (15), surrounding the gas piston (13), such that when the gas piston (13) is in the closed position, the spring (15) is compressed and exerts a counter-force to a force caused by air pressure in the tripping device gas compartment (10);
• and tripping device actuation means (14) for alternatively sliding the gas piston (13) between its closed and its open positions;
• d.) the middle chamber (4) further including a pressure release liquid flow orifice (16), leading to an interior liquid compartment (17), for the accumulation of a volume of a pressurized liquid;
• e.) an upper diaphragm (18), positioned between the upper chamber (3) and the middle chamber (4), so as to form a flexible, fluid-tight seal between the interior gas compartment (6) of the upper chamber (3) and the pressure release liquid flow orifice (16) of the middle chamber (4), such that when the interior gas compartment (6) is pressurized, the pressure release liquid flow orifice (16) is sealed, with upper diaphragm (18) further having a gas-side surface (18a), facing the gas compartment (6) and a liquid-side surface (18b), facing the pressure release liquid flow orifice (16), the gas-side surface (18a) and the liquid-side surface (18b) having a surface area that is the same, the surface area being in a ratio to a cross sectional surface area of the pressure release liquid flow orifice (16), of greater than about 20:1;
• f.) the lower chamber (5) further including first and second liquid inlet orifices (19,20) and first and second liquid outlet orifices (21,22), such that the first liquid inlet orifice (19) is in fluid communication, at a first end thereof, with a pressurized liquid supply source, located exterior to the low pressure actuator, and is in fluid communication, at a second end thereof, with a first end of the second liquid inlet orifice (20);
• the second liquid inlet orifice (20) is in fluid communication, at a first end thereof, with the second end of the first liquid inlet orifice (19), and is in fluid communication, at a second end thereof, with the interior liquid compartment (17) of the middle chamber (4);
• the first liquid outlet orifice (21) is in sealable fluid communication, at a first end thereof, with the interior liquid compartment (17) of the middle chamber (4), and is in fluid communication, at a second end thereof, with a first end of the second liquid outlet orifice (22);
• and the second liquid outlet orifice (22) is in fluid communication, at a first end thereof, with the second end of the first liquid outlet orifice (21);
• and is in fluid communication, at a second end thereof, with a liquid receiving sink, located exterior to the low pressure actuator;
• such that there is a fluid channel of communication extending in series from the liquid supply source to the first liquid inlet orifice (19), to the second liquid inlet orifice (20), to the interior liquid compartment (17) of the middle chamber (4), to the first liquid outlet orifice (21), to the second liquid outlet orifice (22), and finally, to the liquid receiving sink;
• g.) a lower diaphragm (23), positioned between the lower chamber (5) and the middle chamber (4), so as to form a flexible fluid-tight seal between the interior liquid compartment (17) of the middle chamber (4) and the first end of the first liquid outlet orifice (21) of the lower chamber (5), such that when the interior liquid compartment (17) is filled with pressurized liquid, liquid pressure is exerted against the lower diaphragm (23), causing the lower diaphragm (23) to seal against a liquid sealing lip (24) adjacent to the first end of the first liquid outlet orifice, further such that liquid is retained in the interior liquid compartment (17) due to gas pressure from pressurized gas in the interior gas compartment (6) of the upper chamber (3), and due to a surface pressure differential caused by the lower diaphragm (23) having a greater surface area than a cross sectional surface area of the first liquid outlet orifice (21) of the lower compartment (5);
• and
• h.) a liquid by-pass outlet orifice (25), extending from the liquid side surface (18b) of the upper diaphragm (18) to the second liquid outlet orifice (22).