Vaccination gun

In a vaccination gun of the type having a vaccine piston pump, drive motor means for driving the pump, said drive motor means being operated by a propellant gas, locking valve means for selectively admitting said propellant gas to said drive motor means, container means for holding said propellant gas, coupler means for coupling said container means with said locking valve means, and housing means housing said container means and coupler means and forming a gun grip;

• the improvement wherein said coupler means includes a chamber fluidically connected between said container means and said locking valve means, flap-valve means loosely a chamber and slidably mounted in said chamber and dividing said chamber into a first portion communicating with said container means and a second portion communicating with said locking valve means, said flap-valve means being responsive to pressure released by said locking valve means to move from a first position in said chamber adjacent said container means to a second position in said chamber adjacent said locking means, said coupler means including means for providing a gas leak from said first portion to said second portion of said chamber;
• and wherein said chamber includes means for sealing against said flap-valve means when in said second position thereby preventing gas flow from said first portion to said second portion except through said means for providing a gas leak whereby, pressure between the first and second portions of the chamber is equalized after said flap-valve means is sealed against said sealing means;
• and biasing means biasing said flap valve means away from said sealing means and toward said first position after said pressure is equalized.