Guericke Air Pump

A vacuum pump is a pump run backwards, and the seal is everything.

1. Bore a barrel 50 mm diameter and 200 mm long from acrylic tube or aluminium.
2. Turn a piston to fit with about 1 mm clearance all round.
3. Cut a leather cup washer and fix it to the piston face so its lip flares OUTWARD against the barrel wall.
4. Oil the leather thoroughly and work it until it is supple.
5. Fit a rod through a guide at the barrel's end.

The lip must face the vacuum side. A cup seal is a one-way device: pressure on the concave side presses the lip harder against the wall, so it seals better the harder it is asked to work. Fit it backwards and it leaks precisely when you need it not to — the same asymmetry as the lip seal in batch 71, three centuries earlier.

Two one-way valves are what turn a syringe into a pump.

1. Cut two thin leather or rubber flaps.
2. Fit the INLET valve at the barrel end connected to the vessel, opening toward the barrel.
3. Fit the OUTLET valve in the piston or the barrel's far end, opening to atmosphere.
4. Test each by blowing through it in both directions.

This is the same two-valve arrangement as Ctesibius' force pump and the grease gun in batch 71. One valve admits from the source on the intake stroke, the other discharges on the return, and neither lets flow reverse. Any reciprocating pump in history is these two valves plus a piston, and the only thing that changes is what is being moved.

Each stroke removes a FRACTION, never a fixed amount — and that changes everything.

1. Connect the pump to a rigid vessel with a gauge or a manometer.
2. Record the pressure after every stroke for the first twenty strokes.
3. Plot pressure against stroke number.
4. Keep pumping and note where the curve flattens.

The pump's ultimate pressure is set by leakage, not by the pump.

1. Pump down to the flattening point and close the valve to the vessel.
2. Watch the pressure over ten minutes and record the rise.
3. Paint suspect joints with soapy water and watch for bubbles being drawn IN.
4. Tighten or re-grease each joint and repeat the rise test.

Otto von Guericke, mayor of Magdeburg, built his air pumps from around 1650 and used them for a series of public demonstrations that changed what educated people believed. The hemispheres are the famous one, but he also showed that a bell in a vacuum makes no sound, that a candle goes out, and that animals cannot survive — establishing that air is a substance with properties rather than simply the absence of things.

The philosophical stakes were the point. Aristotelian physics held that a vacuum was logically impossible; Torricelli's barometer of 1643 had already produced a small one above the mercury, and Guericke's pump made large ones on demand. A machine settling a two-thousand-year-old argument is a rare event, and it is why this pump belongs at the head of the chain.

What it could not do. Guericke's pump reached perhaps a few per cent of atmospheric pressure — impressive, and nowhere near enough for the technologies later in this batch. An incandescent lamp needs pressures thousands of times lower, because a filament in a few per cent of an atmosphere still burns out in seconds. Every step in this chain is someone finding a way past the previous pump's ultimate limit.

Its honest limits: piston pumps are defeated by their own seals and by the volume left in the barrel at the end of a stroke, which re-expands into the vessel. That dead space sets a floor no amount of pumping beats. Later designs attack exactly that — the mercury pump next in this chain has no seals and no dead space at all.