Tim Morris, conservator metal and small technology, is currently working on a model that demonstrates a principle of physics. It was conserved in 1986 using products that would be used if it was to be operated on a regular basis. These products were designed for optimum operation of the object, not necessarily for the longevity of the object. This approach was best practise at the time.
Object 86/612
Conservation trends have changed since then. We do have operational objects at the Powerhouse Museum such as steam engines and musical instruments. However, most that were once operational have been ‘mothballed’ so they do not sustain further damage.
The products used in the early treatment of this item were not inert. The grease has acted as an electrolyte and has caused the brass to dezinc, observed as the green colour on the object in the photo.
Tim dismantled the object and took samples of the grease and tested it for chlorides. Fortunately the tests were negative. A positive result for chlorides would have indicated the grease had chemically bonded to the metal and would require vigorous treatment. However in this case, the remaining grease was then removed with solvents, detailed photos were taken of the corrosion, and the corrosion was reduced mechanically.
The object was reassembled and lubricated using a medical (archival) grade petroleum jelly. This will protect the moving parts but will not harm the metal. The object can occasionally be used for demonstration.
I think it must be a vacuum pump – possibly a two stage pump. It looks like winding the handle will make one plunger move out while the other moves in and then continuing the winding, the movements would swap. There must be a valve somewhere for each cylinder so that the partial vacuum gradually improves. There seem to be two bases as if there might be a second sphere – not shown – that resembles the one shown which has a tap. The grease that is mentioned would be to improve the plunger action by completing the seal.