A pressure testing system for pressurizing and testing a test vessel using a pump driven by pneumatic pressure and having a pressurized hydraulic fluid outlet to the test vessel, the pressure testing system comprising: a hydraulic pressure transducer coupled to the hydraulic fluid outlet to generate a hydraulic pressure signal indicative of hydraulic pressure at the test vessel; and a pneumatic control unit configured to drive the hydraulic pump via a supply of pressurized air, the pneumatic control unit comprising: a pneumatic regulator disposed to modulate a pneumatic pressure of the pressurized air toward a target pneumatic pressure; and a pneumatic pressure transducer configured to sense a pneumatic pressure of the pressurized air output by the pneumatic regulator, compare the sensed pneumatic pressure with the target pneumatic pressure, and adjust the output of the pneumatic regulator; control circuitry; wherein the pneumatic pressure transducer is configured to adjust the output of the pneumatic regulator if the sensed pneumatic pressure is above or below the target pneumatic pressure, as based on a control signal from the control circuitry, to iteratively or continuously drive the sensed pneumatic pressure towards the target pneumatic pressure; characterised in that the control circuitry is configured to receive the hydraulic pressure signal, set the target pneumatic pressure based on a target hydraulic pressure at the test vessel, and iteratively increase the target pneumatic pressure until hydraulic pressure signal exceeds the target hydraulic pressure. a hydraulic pressure transducer coupled to the hydraulic fluid outlet to generate a hydraulic pressure signal indicative of hydraulic pressure at the test vessel; and a pneumatic control unit configured to drive the hydraulic pump via a supply of pressurized air, the pneumatic control unit comprising: a pneumatic regulator disposed to modulate a pneumatic pressure of the pressurized air toward a target pneumatic pressure; and a pneumatic pressure transducer configured to sense a pneumatic pressure of the pressurized air output by the pneumatic regulator, compare the sensed pneumatic pressure with the target pneumatic pressure, and adjust the output of the pneumatic regulator; control circuitry; wherein the pneumatic pressure transducer is configured to adjust the output of the pneumatic regulator if the sensed pneumatic pressure is above or below the target pneumatic pressure, as based on a control signal from the control circuitry, to iteratively or continuously drive the sensed pneumatic pressure towards the target pneumatic pressure; characterised in that the control circuitry is configured to receive the hydraulic pressure signal, set the target pneumatic pressure based on a target hydraulic pressure at the test vessel, and iteratively increase the target pneumatic pressure until hydraulic pressure signal exceeds the target hydraulic pressure. a pneumatic regulator disposed to modulate a pneumatic pressure of the pressurized air toward a target pneumatic pressure; and a pneumatic pressure transducer configured to sense a pneumatic pressure of the pressurized air output by the pneumatic regulator, compare the sensed pneumatic pressure with the target pneumatic pressure, and adjust the output of the pneumatic regulator; control circuitry; wherein the pneumatic pressure transducer is configured to adjust the output of the pneumatic regulator if the sensed pneumatic pressure is above or below the target pneumatic pressure, as based on a control signal from the control circuitry, to iteratively or continuously drive the sensed pneumatic pressure towards the target pneumatic pressure; characterised in that the control circuitry is configured to receive the hydraulic pressure signal, set the target pneumatic pressure based on a target hydraulic pressure at the test vessel, and iteratively increase the target pneumatic pressure until hydraulic pressure signal exceeds the target hydraulic pressure.