The key to the entire mechanical assembly was a single wrought-iron locking pin, six inches long and an inch thick, that held the brass ratchet arm in its raised position. As long as that pin remained locked in its slot, the clockwork mechanism would continue to turn, holding the siphon pallet open against the river's pressure.
Bramble floated eighteen inches from the valve housing, inspecting the iron pin with his nose and forepaws.
The pin was slick with machine grease, but it had not been welded in place. It had been designed to be removable from above by a long iron reach-rod so the engineers could service the valve during maintenance. At the head of the pin was a heavy, square-cut iron ring, about two inches wide—large enough for a human hand to hook into with a boat hook.
Bramble reached out with his right forepaw and touched the iron ring. His sharp, curved claws slipped easily into the open centre of the square ring. He gave a gentle tug.
The pin didn't move. The heavy water pressure against the brass siphon pallet was pinning the locking bar tightly against the iron housing, creating friction that no small animal could overcome by direct pulling. Bramble sat back on his hind legs on the canal bed, his tail fanning the water slowly to maintain his depth.
He was thirty-one inches long from snout to tail-tip, and weighed barely fourteen pounds. He could not pull an iron pin against five hundred pounds of water pressure by brute force alone. He needed leverage.
He looked around the bed of the canal. Three feet to his left, lying half-buried in the river silt, was an old iron coupling link from a broken barge chain—a solid bar of wrought iron six inches long with a tapered, wedge-shaped end.
It had been discarded years ago during the construction of the lock wall, and its surface was pitted with rust, but the metal core remained thick and unyielding.
Bramble swam over, gripped the coupling bar in his strong jaws, and pulled it free from the mud. He carried it back to the siphon housing, holding it firmly between his teeth. He tested the fit: the wedge end was thin enough to slide into the narrow gap beneath the iron ring.
If he could position the bar correctly and use his full body weight as a lever, he might just break the friction hold. He pushed the wedge in with his nose, making sure it was centered between the square head and the iron casing. The fit was tight, but the angle was correct.
Now all he needed was the right moment—and the full strength of his back and legs. The barge coupling link was seven inches long and forged from three-quarter-inch wrought iron bar. It had a natural curve at one end where it had hooked into the towing chain of a horse-drawn coal barge.
The surface was covered in small orange spots of iron oxide, but the core was rock-solid. Bramble carried it in his jaws, balancing the weight carefully so it didn't catch against his leather harness. He approached the valve assembly from the lee side, where the water current was slightly less intense.
He set the bar down on the flat granite coping stone at the base of the frame, taking a moment to flex his aching jaw muscles. He examined the alignment of the iron locking pin once more. The pin was inserted at a fifteen-degree angle into the brass ratchet block, held in place by a heavy steel retaining spring.
If he could get the wedge end of the iron bar under the head of the pin, he could use the stone foundation block as a fulcrum. The barge coupling bar had been forged from solid Staffordshire wrought iron, hammered into shape by skilled smiths. It had a natural curve at one end that fitted Bramble's paw grip perfectly.
He swam around the housing twice to test the angle of approach. He knew that in fluid mechanics, leverage was everything: a small force applied at the correct angle could dislodge an object holding hundreds of pounds of static pressure. He positioned the wedge end under the iron ring and prepared for his moment.
Bramble surfaced beneath the arched brick vault, shaking the cold water from his whiskers as he examined the heavy brass valve assembly bolted to the canal wall. The mechanism was not standard lock-keeper equipment. Its gears bore the stamp of industrial manufacture, designed to operate without any surface indicator — hidden entirely beneath the waterline where no canal inspector would notice it during routine checks.