Yes all pressure caps are pressure release and will allow coolant to escape. Caps used with recovery systems have the added seal mentioned above that actually works in reverse to the pressure cap release to allow the coolant to return to the radiator from the recovery tank. This smaller valve perse' seals under the pressure to escape allowing the major seal of the cap to allow the fluid to escape to the tank and upon cool down a vacume is formed in the radiator opening this seal and allowing the coolant back in.
