With the collar backed off and the frost cleared, Mara could see the seat.
She lay on her side on the grating with her face close to the valve, the hand lamp from Sera’s belt clipped to her visor rim, and looked up into the gap between the collar and the body. The seat was a ring of dull grey metal, softer than the valve’s body, and across it, from one side almost to the other, ran a crack. Fine, dark, ragged at its edges, like a hair laid across the metal. The cold came out of it in a thin white thread.
She unclipped the lamp from her visor.
“Orison. Is there a replacement seat? A seal? Anything that fits this bore?”
“No,” Orison said.
It said it at once, without the usual pause. Then, after a moment, as if it felt it owed her more:
“There were seals. A stock of them, in the stores behind the second chamber. Seals, seats, gaskets, collars. The forge used them.” A pause. “The forge has spent its stock. Over centuries, I believe. Each repair took one, and no new ones came. I was waiting for a smith who would make more. A smith did not come.” The voice went quieter. “I cannot say how long that took. I have records of many repairs and no records of the smith arriving. I believe the waiting went on for a very long time.”
Mara lay on the grating and looked at the crack.
“So there’s nothing,” she said.
“There is nothing in the stores. I am sorry.”
She sat up. She looked at the valve, at her own small pile of tools beside it, the gauge and the wrench and the rag and the notebook. Nothing there that would make a seat.
Sera was standing over her. She had been quiet through all of this, holding the valve key on the stem. Now she let go of the key and reached into the thigh pocket of her suit, an awkward motion in the stiff fabric, and came out with something in her gloved fist. She held it out.
It was a clasp. A steel clasp, the size of her palm, heavy, with a curved body and a hinged tongue, scorched along one edge. Mara knew it before Sera opened her hand. It was from the courier’s ship. The hatch clasp, or part of it, from the hatch Sera had cut open in the conveyor fields.
“I took it,” Sera said. “Off the hatch, when it fell. Before the crews came.” She turned it in the lamp light. “Rescue habit. Good metal shouldn’t be wasted. And I don’t leave things on a field that can tell someone what happened there.” She held it out further. “It’s good steel. Courier-grade. They don’t skimp on hatch hardware.”
Mara took it. It was cold and heavy and smooth under her glove, and she turned it over and looked at the curve of its body. Thick enough. The right kind of steel, hard but not brittle. If she cut the body down, filed a ring out of it, shaped it to the bore.
“Don’t wreck my clasp,” Sera said.
“I’ll have to cut it.”
“Then cut it well.”
Mara took it to the bench. There was a bench in the lowest chamber, against the side wall: a slab of the same pale alloy as the valve, waist high, scored with old tool marks, and fixed to one end of it a vise. She had noticed it when they came in and wondered who had last used it. She clamped the clasp in the vise and took the small hacksaw from the Tern’s kit and began.
It took a long time. The steel was good and hard, as Sera had said, and the cold in the chamber made her fingers stiff even through the gloves, and she had to stop every few minutes and put her hands under her arms. She cut the tongue off first, then the hinge, until she had only the curved body. Then she cut a section from the body, a flat piece, and began to file.
She filed it round. Slowly, a few strokes at a time, holding it up against the lamp between passes, turning it, filing again. She wanted a ring that would fit the valve’s bore exactly, sit on the valve’s body where the old seat sat, and take the plug’s pressure when the valve closed. She rounded the inner edge against the bore itself, taking it to the valve and trying it, taking it back to the bench, filing, trying again.
When she thought it was close she checked the fit two ways. First with her thumbnail: she slid the ring into the bore and ran her nail around the joint between the ring and the body, feeling for a gap, a ridge, anything that would let the cold through. Then with the file: she tapped the ring lightly with the file’s tip, at four points around its circumference, and listened. Tink. Tink. Tink. Tink. All four the same. A ring that sat evenly. If it had been high on one side, that side would have rung brighter.
It was the cool-edge test, more or less. Tavin’s test, the first thing he had taught her. She had not expected to use it at the bottom of a sun.
She fitted the ring into the valve as the new seat, on top of the cracked one. She left the old seat where it was; she had no idea how it was fixed, and she would not break anything she did not understand. She laid the courier’s steel over the cracked seat and brought the collar back down on top of it, gently, a quarter turn at a time, listening to the pipe’s note with her palm. When the note was round and steady, she stopped. Just enough, short of tight.
“Open the stem,” she said. “Slowly. A quarter.”
Sera opened it.
The hiss came back. Thinner. Much thinner. Mara watched the joint, and the white thread of escaping cold that had been pouring from the crack dwindled to a wisp, a breath, almost nothing.
“Half,” Mara said.
Sera opened it to half.
The hiss rose. The wisp became a thread again. And Mara, with her palm on the pipe, felt the new seat begin to move. Only a shiver. The courier’s steel was good, but it was not a seat; it was a filed piece of a hatch clasp lying on a cracked ring, and at half pressure it was beginning to lift.
“Back,” she said. “Back to the quarter.”
Sera closed it. The hiss dropped. The thread became a wisp. The shiver under Mara’s palm stopped.
She sat back. She looked at the gauge, still on the test port. She read the number. She looked at the valve. Then she took out her notebook and wrote, carefully, before she said anything.
She looked up at the ceiling grille.
“Orison. It holds at low pressure. At a quarter open, it holds. The leak’s down to a thread. Above a quarter, the seat lifts. It won’t hold.” She held up the notebook, though the keeper could not see it. “Low pressure only. I’ve written the limit. Don’t push it past the line I wrote.”
The grille was silent.
She waited. She had expected something else, she realized: that she would have to explain why a quarter was not good enough, or argue that it was better than nothing, or defend a repair that had only half worked. She had expected the forge to want a fix and to be disappointed by a patch.
“You named the weakness correctly,” Orison said.
Its voice was quiet. Almost wondering.
“You did not tell me it was repaired. You told me what it would do and what it would not. You told me where it would fail.” A pause. “I have had visitors. Long ago. They told me things were fixed. Some of them were. Some of them were not. None of them told me the limit.” Another pause. “I have not had a visitor do that in a long time. I believe I have never had a visitor do that.”
Mara had nothing to say to that.
“I am writing it down,” Orison said. “The valve: temporary seat, courier steel, low pressure only. The visitor: named the weakness. I am writing them on the same line.”
Sera, beside her, said nothing. But Mara saw her looking at the valve with an expression that was not quite approval and not quite surprise, the look she had given the claw in the yard after the tenth stroke.
The leak was a thread. A wisp. The frost on the floor had stopped spreading, and as Mara watched, the edges of it began, very slowly, to soften.
She looked down at her notebook. Under LORN, under the gauge readings, she had written: Valve, lowest chamber. Seat cracked. Temporary seat filed from courier hatch clasp (Sera’s). Holds at 1/4 open. Lifts above. LOW PRESSURE ONLY.
She underlined the last three words. Then she underlined them again.