Vaughan states that the GWR investigated the effectiveness of varying train speed, and found that 45 mph was the optimum speed; but water could be picked up successfully as low as 15 mph. At that speed 944 gallons could be picked up in 440 yards, but Vaughan suggests that this is a low theoretical figure, and that it overlooks the bow wave effect which enables a greater take-up rate. There was a significant resistance to the forward motion of the engine during the process, enough to require special care by the driver to avoid problems on unfitted freight trains.