Ada Morland didn’t look at the receding cellar water with the relief of an amateur. She took her four-dial brass test pipe hub, knelt in the wet silt beside the cast-iron valve collar. Then she clamped a copper snubber line to the small threaded test cock Hal Rook had drilled into the upstream pipe wall forty years ago.
The black needle on her main gauge kicked wildly. It didn’t settle at forty-two PSI. It spiked past fifty, fluttered erratically against the internal damping oil, and locked firmly at fifty-eight PSI.
The cellar smelled heavily of damp wet stonework, cold soot, and the sharp, stone tang of copper green rust leaching from the old test cock. On the wall above the valve, a long, upright crack ran through the lime mortar, weeping tiny streams of chalky white pipe lime. The stonework shook under the high-pressure load.
‘Fifty-eight pounds,’ Ada said. Her voice dropped into the grim, clipped rhythm she used when inspecting cracked steam boilers in Huddersfield mills. ‘And climbing. Look at that pointer flutter, Pella. That isn’t static head. That’s a sound rebound wave.’
Pella knelt beside her, the wet knees of her trousers soaking through with cold drain water. She touched the copper snubber tube. She could feel the metal shaking with a high-hum, metal hum that sounded like a distant harp string stretched to the point of snapping.
‘The water stopped coming into the cellar,’ Pella said, trying to reconcile the gauge reading with the drying floorboards around them. ‘The flap valve is closed solid. The sump is draining.’
‘The flap is closed here,’ Ada said. She tapped the dial glass with the tip of her brass drift. ‘Which means we just slammed an iron door in the face of a high-pressure water column moving at six feet per second. In a closed high-pressure system, water is incompressible. When you stop a moving column instantly without an air cushion or a spreading chamber, where does the striking force go?’
Pella’s eyes widened. Her summoner training had focused on spiritual deep ring and elemental holding formulas. But the physics of fluid driving force had been hammered into her by her father’s notebooks. ‘High-pressure ram. The blast wave travels backward along the pipe.’
‘Ten out of ten, girl,’ Ada said grimly. ‘Sound wave speed in cast-iron pipe is nearly four thousand feet per second. That blast wave is traveling straight back up the town relief under-road drain toward Fish Street. It will hit every rusted elbow, every thin-walled joint. Every rusted through lead solder seal between here and the High Terrace.’
Eren leaned his heavy pry bar against the wall, listening to the floorboards. Beneath their feet, a series of rhythmic, metal thuds began echoing through the bedrock—clonk... Clonk... Clonk—spaced two seconds apart, like someone swinging a sledgehammer against an underground anvil.
The silt stench from the receding puddles was already drying in the cellar air. But the shakes traveling through the stone were growing distinctly stronger. Tavi dropped to his hands and knees on the drying flat stone slabs. It pressed his ear directly against an oak wooden props block.
‘It sounds like someone trapped in an iron tank,’ Tavi whispered, looking up with wide, frightened eyes. ‘Like they’re hitting the pipes with an axe.’
‘That’s Cooper Lane,’ Eren said, his face pale beneath the soot. ‘The old lead service pipe that runs beneath the bakery cellar. It was laid sixty years ago with soft wiped joints.’
‘If that blast wave hits the bakery line without a bypass,’ Ada warned, ‘it will shear the lead sleeve clean off the stonework. Within twenty minutes, the baker’s flour store will have three feet of boiling stone water across the floor. His foundation footings will wash out into the gutter.’
She reached into her pocket, pulled out a grease pencil. Then she quickly sketched a high-pressure circuit on the dry side of Eren’s timber wooden props balk. ‘Here is your under-road drain line. Here is the flap valve we just dropped. And here is where the moving wave bounces. If you leave this pipe dead-ended, the pressure will compound with every pulse from the College drain tube until something ruptures.’
Ada pointed to the threaded check plug on top of the cast-iron collar. ‘Hal Rook put a three-inch tapped boss right here above the seating. He intended it for a sound relief valve, but the College never installed the fitting. That boss is plugged with a square-headed iron bolt.’
‘If we back that bolt out,’ Eren said, studying the sketch, ‘we can tap a three-inch branch water chute into it without touching the main collar bolts.’
‘Exactly,’ Ada said. ‘You tap that boss, run an open wooden water chute out through the coal chute into the yard, and let the blast wave dump its head into an unsealed volume. You don’t try to hold fifty-eight pounds of head with wood. You give it sky relief.’
She checked the collar’s clockwork limit with her drift. ‘A wooden water chute will flex enough to absorb the pulse cycles. Water will surge three feet up the sides during the wave peak, then drop back as the line vents. That keeps the pressure on the bakery line below thirty PSI. It their old lead joints can tolerate.’
Eren pulled out his folding boxwood carpenter’s rule, snapping the brass joints into a straight six-foot gauge. ‘I have forty feet of tongue-and-groove cedar plank in the yard, Ada. If we nail the water chute into a U-trough with boiled pitch along the bottom seams, it will carry two hundred gallons a minute without leaking a cupful onto the cobblestones.’
She stood up, checking her stopwatch. Three minutes and fourteen seconds remained before the arch’s pullback countdown reached zero. She packed her pipe hub into its wooden carrying case, clicked the brass latches shut. Then she pointed her grease pencil directly at Pella’s chest.
‘Listen to me, Pella Rook. This is the difference between a real plumber and a cowboy who just turns off a stopcock and runs away with the cash. You can’t just block a river, girl. You have to give it somewhere polite to go.’
Pella felt the cold air from the street above cutting through the cellar steam. ‘Where can it go? We can’t vent it into the street. The town guards would arrest us for public endangerment.’
‘What sits behind this boarding house?’ Ada demanded, turning to Eren.
‘An abandoned rainwater water tank,’ Eren answered instantly. ‘Built by the old ferry company in 1860 to wash carriage wheels. Ten thousand gallons capacity, lined with dry stone and high-pressure lime. It’s been empty since the city brought piped water down the hill.’
‘Is the overflow line still intact?’ Ada asked.
‘There’s a twelve-inch timber water chute running from Orv’s yard straight into the water tank vault,’ Eren said, his carpenter’s mind already calculating angles and falls. ‘I boarded over the top hatch two years ago to keep children from falling in.’
‘Then you rig a bypass water chute before that pressure gauge hits sixty-five pounds,’ Ada said, pulling off her reed gauntlets and thrusting her tools into her canvas roll. ‘You drill a three-inch relief hole above the flap collar, run a wooden diversion trough into that water tank, and let the blast wave dump its head into ten thousand gallons of empty air.’
The brass arch in Sister Merrow’s washroom down the lane was already chiming its one-minute warning, the high-pitched ringing shakes traveling through the stone foundations and humming in the soles of their boots.
Ada zipped her overalls, turned toward the basement stairs. Then she paused on the bottom step to look back at Pella. ‘You took seven silver coins from Master Orv, girl. Four of them are sitting in your pocket right now. That coin isn’t profit until the street is safe. If you let the baker drown because you cleared Orv’s coal bunker, you’re no better than Master Sorell.’
Pella gripped her drafting board against her ribs, her jaw setting into a hard, resolute line. ‘The water tank will be flowing before the hour strikes, Ada. I promise.’
Ada nodded once, a sharp, approving jerk of her chin. ‘Good. Keep your bypass water chute at a four-inch fall per rod, and don’t let Eren skimp on the timber bracing. I have a district heating check in Harrowby at two o’clock, and I don’t want to come back tomorrow to find Lowbank floating in the harbor.’
She climbed the stairs with long, hurried strides. Her rubber boots splashed through the leftover puddles. In the street above, the rain had slowed to a steady mist. But the metal clonk of the high-pressure blast wave was already echoing through the iron street grates along Fish Street. Two wagon drivers had stopped their horses. They stared down at the cobblestones as though expecting the earth to split.
Pella turned to Eren, whose face was already set with the fierce determination of a man facing a failing dam.
‘You heard the lady, Eren,’ Pella said, reaching for her adze. ‘Get the auger and the cedar planks. We have twenty minutes to build an overflow water chute before Cooper Lane explodes.’