A combustion-powered tool comprises a primary combustion chamber, a secondary combustion chamber, and a working piston that is in fluidic connection with the secondary combustion chamber so as to be exposed to the pressures developed within the secondary combustion chamber, when combustion takes place within the secondary combustion chamber, such that the working piston can be driven through its working or power stroke. A flexible silicone rubber plate-type control check valve is interposed between the primary combustion chamber and the secondary combustion chamber so as to control the flow of combustion products from the primary combustion chamber into the secondary combustion chamber and yet prevent the flow of combustion products from the secondary combustion chamber back into the primary combustion chamber, when combustion occurs within the secondary combustion chamber, such that the pressures developed within the secondary combustion chamber, as a result of the combustion of the air/fuel mixture within the secondary combustion chamber, can in fact act upon the working piston so as to drive the same through its working or power stroke.