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Testing Pouches and Pouch Sealants

At the outset, it must be stated that testing pouches in a truly scientific manner would require expensive laboratory-quality testing equipment. It must also be stated that there are at least two characteristics of a pouch that are important: air-tightness and sensitivity. Naturally, a third characteristic of importance is longevity, but that will not be addressed in this treatise. A fourth characteristic has to do with the size of the pouch as it relates to the weight of the valve, but that aspect is left to the engineers who design player systems.

As a side note, a reasonable question that one might ask is, "Why does a pouch need to be sealed?" The answer is fairly simple. Back in the 1920's, when player pianos were very popular, animals were raised in a specific manner to produce tan pneumatic leather that was very supple and quite air-tight. This was possible because there was a great demand for that type of leather. Today, that demand doesn't exist. So, the leather that 'is' available is much more porous. It leaks! Therefore, the skins used to make pouches (or the pouches themselves) need to be sealed. Also, there may be occasions when it is more desirable to seal an old pouch than replace it with a new one. (I'm not here to debate the prudence of that action.)

An initial problem one encounters when testing pouches is the leather itself. No matter how big or small the pieces might be, no two pieces of leather are 'identical'. So, even if quality testing equipment was available, the results would be skewed because of the differences in the test subjects. Be that as it may, it is my hope that the differences in the sealants will be so profound that the minute differences in the test subjects will be, by comparison, insignificant.

Leather pouches rarely 'fail', and it's almost impossible to accurately test them (in place) because of other factors which work in conjunction with the operation of a pouch: Namely, the bleed and the pouch well. On the other hand, pouches 'can' get so 'worn out' that they leak to the point where they become 'ineffective', or lose the 'power' required to activate (or move) the valve. More on that later....

In the case of the Simplex, testing is a little easier because the bleed is located in the main valve board. So, that only leaves the pouch well. However, because of its advanced age, the wood in the Simplex valve/pneumatic block is often the chief source of problems. That's because as all wood ages it dries out, and as that happens, atmospheric air leaks into block 'through' the wood causing the valve to become less and less responsive. For this reason, it is recommended that all internal air passages be sealed with a sealer like Phenoseal when a block is rebuilt.

As a side note, although slightly less of a problem, the Simplex also has a reputation of having internal leakage where the metal intake valve seat (a type of grommet) is connected to the wood. But here again, the problem is actually wood shrinkage due to age, and also here again the corrective action is to seal the grommet in place with a sealer like Phenoseal.

As for the tool used to set the pouch, I can special order a pnuematic (or vacuum operated) pouch setter from my supplier. It sells for $63.00 plus the cost of shipping.

Concerning working on the Simplex valve unit, I have a number of web pages at:

Simplex Problems
Simplex Leaks
Simplex 1
Simplex 2

Hope this is helpful.

Musically,

John A Tuttle
Player-Care.com

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