Failure to fire can be the result of several unrelated conditions:

1) No power. Lack of power connection is the most common reason for not firing.
Vernier Projectile Launcher
The launcher gets power from an interface (by way of the interface cable) or by direct power using a LabQuest® Power Supply (LQ3-PS).

Go Direct Projectile Launcher
The Go Direct Projectile launcher gets power from the USB connection to a USB outlet, USB power brick, or active USB port.

2) Not pressing both buttons simultaneously. You must simultaneously press the Arm and Launch buttons to fire. We recommend first pressing and holding the Arm button and then pressing the Launch button.

3) Pressure too high. Use a pressure in the system of less than the maximum working pressure of approximately 110 psi. If the pressure is higher than the recommended pressure, the launcher may not launch. This is normal. In such a case, use the pressure relief button on the supplied pump to drop the pressure below the maximum working pressure.

4) Pressure too low. Sometimes new launchers won’t fire reliably until the pressure knob is adjusted. If first attempts to fire fail, change the pressure by turning the pressure knob a turn counter-clockwise, release excess pressure as in step 3, and try again. If pressure is less than 50 psi, turn the knob clockwise and pump up again. Test for firing.

5) Power connection to LabPro, but no power from interface. (Vernier Projectile Launcher only)
The LabPro interface has aggressive power management behavior. Even if the LabPro has power and is connected to the Vernier Projectile Launcher, the digital sensor port on the LabPro will not provide power unless LabPro is communicating with Logger Pro on a computer.

6) Equipment failure. If it still continues to not launch, the launcher may need repair. Contact Vernier.