Two-fluid nonflammable hydraulic system

A method of at least reducing the likelihood of a hydraulic fire in a hydraulic actuator system, in which hydraulic pressure is applied through conduit means to an actuator which moves a load, and the actuator is in a high temperature zone and/or the load is the type which generates heat when so moved, while continuing to use in such system a relatively flammable first hydraulic fluid which is otherwise desirable, comprising:

• positioning a mechanical isolater in the conduit means of a type comprising a housing and a piston movable in said housing, and dividing said housing into a first chamber on one side of the piston and a second chamber on the opposite side of the piston;
• providing a relatively nonflammable second hydraulic fluid in the system between the piston and the actuator;
• using the relatively flammable hydraulic fluid in the the system to apply pressure to said piston;
• and
• using said piston to transmit the pressure to the second hydraulic fluid.

A method of at least reducing the likelihood of a hydraulic fire in an aircraft ground wheel braking system, in which hydraulic pressure is applied through conduit means to a hydraulic brake on a wheel, and said brake generates heat when applied, while continuing to use in such system a relatively flammable first hydraulic fluid which is otherwise desirable, comprising:

• positioning a mechanical isolater in the conduit means of a type comprising a housing and a piston movable in said housing, and dividing said housing into a first chamber on one side of the piston and a second chamber on the opposite side of the piston;
• providing a relatively nonflammable second hydraulic fluid in the system between the piston and the brake;
• using the relatively flammable hydraulic fluid in the the system to apply pressure to said piston;
• and
• using said piston to transmit the pressure to the second hydraulic fluid.

A hydraulic actuator system, comprising:

• a load;
• a hydraulic actuator connected to said load;
• a pressure transmitter comprising a housing and a piston movable in said housing, and dividing said housing into a first chamber on one side of the piston and a second chamber on the opposite side of the piston;
• a control system including first conduit means containing a first relatively flammable hydraulic fluid at supply pressure, second conduit means containing first hydraulic fluid at return pressure, third conduit means connected to the first chamber of said pressure transmitter, and control valve means for switching between a first position in which the third conduit means is connected to the first conduit means, and a second position in which the third conduit means is connected to said conduit means;
• fourth conduit means interconnected between the second chamber of the pressure transmitter and the actuator;
• and
• a relatively nonflammable second hydraulic fluid within said second chamber, said third conduit means and said actuator,
• whereby movement of the control valve means into its first position will communicate supply pressure provided by the first hydraulic fluid to the piston of said pressure transmitter and said piston will transmit such pressure to the second hydraulic fluid, and the pressurized second hydraulic fluid will move the actuator, and the first hydraulic fluid will be isolated from the high temperature environment at the load.