 In a practical demonstration at Hampstead Road Congreve later elected to deploy an air compressor releasing into one caisson, estimating that one man could achieve raising and lowering in three minutes—the company's enabling act did not permit the installation of stationary steam engines.However it was found the fastest overall time was six minutes and that the effort required rendered the operator "incapable of further exertion".Furthermore, as the operation of the device depended upon air pressure inside the caissons (whether the means of moving them was by varying this air pressure or otherwise) when contractor Henry Maudslay delivered them and they were found to leak air, the scheme failed.