Btukfyl

In terms of context, this airlock would be used on airships which fly at a height in which oxygen levels are too low for humans to live. Within the hull of the airship, stored oxygen would be pumped inside and kept within through insulated walls. However, many still need to go out on to the deck. This would need to be done without the oxygen inside being lost and the inside of the ship being depressurized, and thus, an airlock is needed.

However, as this takes place in a semi-medieval world, would something like this be possible to construct given the technology and knowledge available?

Note that the people creating this would have advanced knowledge of chemicals and gasses as a whole, as well as mechanical technology that consists of levers and pullies.

Leather and grease

Let's forget about the impossibility of flying and concentrate on the question of 'can you build an airlock?

These huge leather bellows show that it is possible to make airtight structures with leather.

This sort of bellows has to contain flap valves that allow passage of air in only one direction.

Airlocks would simply consist of an arrangement of flap valves. Small valves would be used to equalise pressure slowly. Large flap valves supported by wooden panels would act as doors. Of course, every time the outer door was opened some air would be lost to the outside but that's true of high-tech space airlocks anyway.

The flaps would need to be kept supple and airtight by the application of a suitable grease. Goose grease would be ideal.

Yes, it is possible to use medieval technology to make an airlock.

Goldbeating is an ancient technology. It can be used to make thin, continuous sheets of metal, including cheaper metals like copper or brass. The interior of the airlock can be "gilded" with this "imitation leaf" to minimize air loss through the walls. Ideally, the leaf would be protected from damage on both sides by sturdier materials.

Large pieces of leaf can be attached to adjacent pieces of leaf by multiple-layer crimps. A practical modern-day example is use of two side-by-side sheets of crimped-together aluminum foil to protect the bottom of a roasting pan from drippings. This makes it much easier to clean the roasting pan after the meal is cooked.

The gilding is not a structural material. Instead, it is a thin layer over structural materials that are porous, leaky, or outgas too much. Tongue-in-groove plywood or the materials suggested by Hippeus_Lancer could be used as backing layers. Studs or other structural framing could back-up the sheet goods. The hardest part of the design would by allowing for expansion and contraction of the backing layers, without tearing holes in the gilding. Fortunately, laminated wood is an ancient technology that mitigates expansion and contraction.

The gilding would be applied the main surfaces of the doorways, but would not be used to seal around the edges of the doorways. The seals around the edges of the doorways would be air-tight gaskets.

Vacuum-tight gaskets can be made using metal. In fact, the "hardest" vacuums are retained by metal gaskets, not rubber gaskets. The fundamental technologies for making a "knife-edge" gasket are knife making, vises or clamps, and copper billets. Medieval metal workers should be capable of making such gaskets.

No, you can't build something like that with medieval technologies.

First of all, a medieval ship is made of wood. Assembling wood to make it airtight can hardly work, for a series of reasons:

• large manufacturing tolerances


• deformation over time


• deformation under stress (a pressurized vessel acts like a balloon)

Same holds for doors and windows. Moreover, while you could use pitch for sealing the gaps between fixed parts, you would have no way to seal the gaps with a movable part (like the door and its frame).

Then we come to the other problem: lacking any electronic you could only pump Oxygen with no control on the flow.

Pumping Oxygen in an environment made of wood with no control is a really poor idea, as the slightest ignition source can cause a huge fire. And guess what they used in medieval time for lighting applications? Flames!

Last problem: how would you separate Oxygen from the air? You have just elementary pumps and loose tolerances for metal crafting, and storing liquid gases requires way more than that.

Modern airlock uses rubber seals.

Your people can use leather with some padding inside, or same material as the airship envelope, inflated using the same means.

Couple questions for you: once out of airlock, how will the person breathe? Oxygen tanks are way beyond medieval technology. Maybe they can trail an air hose, but that requires better materials than door seal

Also, if air is too thin to breathe, it might be too thin to support an airship. You would need to carry composed gas and realise it into the envelope when going up, and when going down, you would waste it into outside air, or try to pump it back into the tanks. And compressing air is beyond medieval technology.

Finally, how well you move around without an engine? Pedal power?

Since your airship is still in atmosphere a perfect seal isnt neccesary unless your pressurized ship plans to stay up that high for days at a time. Using medieval materials like tar, pitch, cork, and rubber can give you a reasonable, but not perfect seal. You’ll be leaking atmosphere, but thats not a huge problem unless you plan to stay up indefinitely.

If your people have mastered airship technology then perhaps they have pressure vessels as well? Several canisters of pressurized air could help extend the length of time you can spend up so high.

A small pool of water between inside and outside where the hull touches down to the surface of the water. You could also build it as a water-filled, U-shaped tunnel where one end is on the inside and the other on the outside. Crew members have to dive through it to enter and exit the ship.

Of course this adds quite some mass (water is heavy) and as others have pointed out in the comments, if you can build an airship and store oxygen you can also build an airlock.