Pneumatically controlled air grease gun

An air grease gun comprising:

• a grip having a generally inverted Y-shaped air passage formed therethrough a trigger-controlled valve installed in said air passage and normally closing said air passage, a trigger actuatable to activate said valve so as to open said air passage, and a valve spring biasing said valve to close said air passage, said air passage being bifurcated into a first branch and a second branch at a lower end portion of said grip so as to define an upper section of said air passage above said first and second branches in such a manner that said valve is installed in said upper section of said air passage, said first branch of said air passage having an inlet adapted to accept compressed air from a compressed air source;
• a hollow barrel coupled with said grip and including a diameter-reduced grease outlet portion located at a front end portion thereof, a partition having a central hole and secured in said barrel in such a manner that a grease-tight seal is established between a peripheral wall of said barrel and said partition, so as to define a grease passage space in front of said partition in said barrel, a barrel piston slidably mounted within a rear end portion of said barrel behind said partition so as to define a rear air chamber behind said barrel piston in said barrel, a piston rod positioned in said barrel and having a front end portion extending through said central hole of said partition and a rear end securely connected to said barrel piston, a barrel spring sleeved on said piston rod in in said barrel between said partition and said barrel piston so as to bias said barrel piston to move rearward, and a pressure relief device relieving air pressure in said rear air chamber of said barrel when the air pressure increases beyond a predetermined value so that said piston spring can bias said barrel piston to move rearward, said rear air chamber of said barrel being communicated with said upper section of said air passage of said grip, a grease-tight seal being established between said piston rod and said partition, said piston rod end portion being capable of moving into said diameter-reduced grease outlet portion of said barrel so as to impel grease out of said grease passage space;
• a spout pipe unit connected securely to the front end portion of said barrel and having spout outlet formed in a front end of said spout pipe unit, and an interior bore which is formed through said spout pipe unit and which is communicated with said grease passage space of said barrel, said interior bore having a large-diameter front section and a small-diameter rear section which is connected to and located just behind said large diameter front section and which has a diameter smaller than that of said large-diameter from section;
• a generally vertical grease storage tube coupled with the front end portion of said barrel at an upper end thereof and including a bottom end wall with an opening, a longitudinal guide rod removably mounted in a central portion of said grease storage tube, and a generally horizontal tube piston mounted slidably within said grease storage tube so as to define a grease storage chamber above said tube piston and a lower air chamber under said tube piston in said grease storage tube, said grease storage chamber being communicated with said grease passage space of said barrel, said tube piston having a central hole formed therethrough through which said guide rod extends in such a manner that grease-tight seal is established between said guide rod and said tube piston;
• an air tube coupled with the lower end portion of said barrel at an end thereof and with the lower end portion of said grease storage tube at the other end so as to intercommunicate said second branch of said air passage of said barrel and said lower air chamber of said grease storage tube, thereby permitting compressed air from the compressed air source to flow into said lower air chamber in said grease storage tube via said first and second branches of said air passage of said grip and via said air tube in order to move said tube piston upward;
• a ball accommodated in said large-diameter front section of said interior bore of said spout pipe unit;
• and
• a ball spring disposed in said large diameter front section of said interior bore of said spout pipe unit so as to bias said ball to close a front end of said small-diameter rear section of said interior bore of said spout pipe unit, thereby preventing grease in said small-diameter rear section from forward movement to said spout outlet of said spout pipe unit through said large-diameter front section unless an additional force is applied to the grease in said small-diameter rear section, a compression force of said ball spring being larger than a pushing force of said tube piston toward grease in said grease storage chamber of said grease storage tube so as to prevent grease coming from said grease storage tube from accessing said spout outlet of said spout pipe unit unless an additional force is applied to the grease in said small-diameter rear section, compressed air flowing from said air passage of said grip into said rear air chamber in said barrel urging said barrel piston and said piston rod forward to impel the grease in said grease passage space into said spout pipe unit so as to move said ball forward, thereby enabling grease to access and move from said spout outlet of said spout pipe.