The early Brayton gas engine had the engine speed governed by varying the point of cut-off for the admission of the combusted gases into the power cylinder, and the admissions of gas and air to the pump was similarly regulated to maintain the reservoir pressure. The liquid fueled engine reported by Clerk only regulated the cut-off to the power cylinder, and used a pressure relief valve to limit the reservoir air pressure. The reservoir on the Brayton engine allowed it to be readily started if it remained pressurized, though Clerk states that "leakage and loss were so frequent that the apparatus was of little use."
