Having taken a peek at the theory behind valves, it’s important to get practical with the materials.
In a Standard / Auto DeLuxe etc double valve system, the two principal valve types found in the stack are the primary valves – which are an outside valve – and the secondary valves, which are an inside valve. The terminology surrounding the player piano components has been the subject of debate; there is a mostly accepted convention about nomenclature, but better to not get bogged down too much for the purposes of this discussion.
The secondary valves are a stem-type valve, which varying methods of how the facings attach to the stem. For the purposes of this post, I am confining my remarks to the facings.
In this system both styles of valves have two facings; in an outside valve both facings seal against a wood seat, in an inside valve the upper facing seals against wood but the lower seals against a metal plate.
Leather against smooth wood is generally a reliable seal, all other factors considered.
Leather against a metal ring is far less forgiving, particularly if the leather is poor quality (uneven, too fuzzy, or stiff, or porous), or if the valve seat area of the metal plate is corroded or not perfectly flat. There are other reasons (beyond choice of leather) as to why the secondary valves require extensive exacting work to get them to perform well. More on that later, perhaps.
At the time of this writing, high quality leather, the kind required for inside lower valves seats (meeting metal plates) is difficult to source as it no longer widely produced and therefore not readily available, even from trade supply houses. Conventional wisdom dictates that this material be a split calf leather with a smooth nap, to prevent lateral leakage.
Some rebuilders have resorted to using thin silicone or neoprene material for lower secondary facings. Like other non-traditional materials it is the subject of controversy, however if it can be made to work in a reliable and durable way – the results are what matter.
For the other leather in primary and upper secondary facings, I have received numerous recommendations for the Columbia Organ Leathers company. I am using it in my stack and find it fit for purpose. I know that others use OSI for their needs. These companies are also able to furnish good leather for other types of valves (not yet discussed) such as flap valves and pallet valves.
Wherever you choose to obtain your materials, make sure to inform yourself about the supplier and their product. Using inferior materials is a fool’s errand as it will waste time and money trying in vain to get good results.
As the prospect of restoring valves strikes terror into the hearts of some inexperienced restorers, they may be tempted to skip over doing it, if the older leather facings “look good”. Older restorers sometimes talk about having gotten away with this omission, when doing a restoration job on a player action when they were starting out.
The difference is that when senior rebuilders worked on players in their youth (e.g. the 1950s or 60s), the pianos in question may have been 30-40 years old. The leather in the valves and gaskets may still have had some life left in it at that time.
After 90 or 100 years, it is a safe bet that all original leather and cloth in the player action need replacing, to function as intended.
The bottom line: you can’t have well performing valves without good materials!