A pneumatic regulator is a device  designed for air rifles  to help improve the consistency between each shot.  This is something many people consider to improve accuracy of the gun.   Regulators do this by metering the amount air entering the valve from the  reservoir of the gun.  The desired pressure is set on the regulator and when it is reached, the regulator automatically stops any more air from the reservoir from entering the valve of the gun.  Once the trigger is pulled, the valve releases the air which propels the pellet.  At this point the valve no longer has any air in it and this triggers the regulator to allow air to pass freely until it reaches the set pressure.  Once again the gun is ready to fire-at the same pressure as the previous shot.  A unregulated gun, will show a power curve and the shot to shot consistency is far less manageable.  This is not the case with a regulated gun and is another reason airgun enthusiasts love regulators.  They offer greater consistency and often increase the shots per charge.  They let you focus on shooting more accurately rather than worrying about where on the power curve the next shot will sit.

What Are Regulators?