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Lock and Cancel Valves
What they do
How they work


One of the more interesting devices in nickelodeon and orchestrions is the Lock-and-Cancel (L/C) valve. L/C valves are also found in Reproducing player pianos, but they are always integral parts of a larger and more complex device. Many types of L/C valves have been invented since the first nickelodeons and orchestrions were produced over 110 years ago. For those who are interested in seeing a number of these devices and how they are manufactured, Craig Brougher has a whole chapter on Lock-and-Cancel valves in his book "The Orchestrion Builder's Manual and pneumatics handbook". However, here we are only going to cover one of the most common types of L/C valves found in nickelodeon 'build-ups', which are basically comprised of two Wurlitzer-type block valves -like the ones pictured above.

The purpose of an L/C valve is really quite simple. It can accurately be compared to a regular On-Off switch of virtually any variety. Simply put, once it's turned 'On', it will stay 'On' until it's turned 'Off". And, it will stay 'Off' until it's turned back 'On'. The major difference between an On-Off switch and a L/V valve is the manner in which it gets turned 'On' and 'Off'. While an 'On-Off' switch is manually activated by a human or other mechanical device, an L/C valve is activated by perforations in a music roll. More precisely, one hole in the roll turns the valve assembly 'On' and another hole in the roll, which is in a different hole position on the roll, turns the assembly 'Off'.

What They Do

Having the ability to turn something 'On' at any particular moment and turn it back 'Off' at a later moment is extremely useful and necessary when it comes to nickelodeon music. While L/C valves are often used for turning various instruments, like an accordion, a honky-tonk rail, or a glockenspiel, 'On' and 'Off' during a song, this treatise will focus on using the L/C valve to control the Rewind and Play (or replay) cycles in a nickelodeon. When used for this purpose, the L/C valve allows the nickelodeon music roll to play through each of the songs on the music roll until the last song has finished playing. Then, a perforation in the roll signals the L/C valve to change state from 'Off' to 'On'. When this happens, the L/C assembly applies vacuum to a bellow which moves gears in the roll transport mechanism, and the music roll starts rewinding. And, since the L/C valve assembly is "locked" 'On', it will continue to apply vacuum to the rewind bellow, which 'holds' the system in Rewind, until it's signaled to change state again. Then, as the music roll nears the end of the rewind cycle, another perforation signals the L/C valve assembly to turn the vacuum to the rewind bellow back 'Off'. This bellow, being spring loaded, then returns the roll transport mechanism to the Play position, completing the cycle.

How They Work

To fully understand how a L/C valve assembly works, you first need to understand how a normal player piano valve functions. If you don't have this basic knowledge, read the information here.

Like a regular 'On-Off' switch an L/C valve assembly has only two positions or "modes". The first mode is referred to as 'inactive'. Referring to the diagram below, in this mode, valve A is 'On' and valve B is 'Off'. In the second mode, valve B is 'On' and valve A is 'Off'. While that sounds simple enough, the question is: How does that work?

Before we get too deep into the explanation of how this device works, it's important to note one critical difference between these valves and regular player valves. As you should recall from the study about regular valves, every valve has its own bleed. The function of the bleed is to allow the pouch to relax very quickly after the valve has been deactivated. However, note that these valves don't have a 'built-in' bleed. Instead, there is a bleed for each pouch in the signal line that connects the atmosphere side of each valve to the pouch well of its mate. Keep this fact in mind as we continue.

In the First Mode, both the Rewind Port and the Play Port are closed. [In other words, there is no signal coming from the trackerbar because the music roll is covering (or closing) both the Play and Rewind ports on the trackerbar.] Also, there is an equal amount of vacuum (marked VAC) being applied to the center chamber of both valve blocks. (Both blocks are connected to a common vacuum source.) Now, if we follow both the 'blue' signal line and the 'green' signal line, we find that both of them provide a path for atmosphere the enter the pouch of their 'sister' block. Therefore, in this state, both valves will begin to activate as soon as vacuum is applied to the assembly. Now here's where it gets a little tricky.

Theoretically speaking, as both valves begin to activate, the signal path from the 'sister' valve block begins to close. If both valve blocks were 100% identical, this would indeed be the case and both valves would end up getting to a state where they were both half-open -or completely balanced- and both would be leaking vacuum to the atmosphere. However, as can be seen in the diagram, they are not 100% identical. In fact, valve block 'B' has an extra port that is labeled 'To Rewind Bellow'. In effect, this is another path to atmosphere because there is atmosphere inside the bellow. And, that being the case, there is an imbalance between to two valve blocks. More precisely, the 'hole' leading to the Rewind Bellow is about 1/2 the diameter of the hole in the top of block B. So, as both valves attempt to close, there is more atmosphere in block B than block A, and that being the case, the valve in block A will close. Once that happens, the path to atmosphere from block A to the pouch in block B closes and the assembly is "Locked OFF".

While the above is true in theory, it was found that there is a much easier and more positive way to insure that block A will always close before block B. This is accomplished by changing the valve clearances of the two valves. By decreasing the valve clearance of block A (or increasing the clearance of the valve in block B), block A will always close before block B. In fact, the valve clearance of block A is typically 1/2 the clearance of the valve in block B, while the valve in block B is set at a normal clearance of between 0.032"-0.040". This presents no problem because the valve in block A only serves one primary function. That function, as will be explained more fully later, is to provide a path for atmosphere to enter into the pouch well of block B. On the other hand, block B requires a normal (if not slightly larger than normal) valve clearance because it's primary function is to operate the Rewind Bellow, which is about three times the size of a normal note bellow and, it must close quickly. But, I'm getting ahead of myself...

So, at this point the assembly is 'Locked Off', and it will stay locked off until the Rewind Port on the trackerbar is opened by a perforation which follows the last song on the music roll. When the Rewind Port opens, atmosphere enters the pouch well in block B, activating its valve. At that moment, two things happen simultaneously. One, vacuum is applied to the Rewind Bellow and it begins to collapse, shifting the roll drive mechanism from the Play mode to the Rewind mode, and the roll begins to rewind. But more importantly, when the valve in block B changes to the 'On' state, the path for atmosphere, that was keeping the valve in block A activated, is closed. And, the same vacuum that is collapsing the Rewind Bellow is now also being channeled to the pouch well in block A. This action causes the valve in block A to deactivate. As soon as that happens, a path to atmosphere (through the hole in the top of block A) is provided to the pouch well in block B (via the green signal line), which keeps the valve in block B activated. In this state, the assembly is "Locked On".

The assembly will stay 'Locked On' until the Play hole in the music roll opens the Play port in the trackerbar which allows atmosphere to enter the pouch well of block A, which activates the valve in block A. And, once again, the assembly is "Locked Off". More completely explained, once the valve in block A activates, the path for atmosphere to the pouch well in block B (which was keeping it activated) is closed. This, is turn, causes the valve in block B to deactivate, which, in turn, provides the path for atmosphere to the pouch well in block A, which keeps the valve in block A activated, or 'Locked On'.

Thought not completely relevant to this treatise, it's important to mention a few more things. First, the Rewind perforation in the music roll is generally about 1/2" in length. It can be that short because the music roll is only traveling at about 7-8 feet per minute and it only takes about 1/4 of a second for the assembly to change from the Locked Off state to the Locked On state. Secondly, the Play perforation in the music roll is generally 3-4 inches in length and there are typically two of them. The two long perforations are typically separated by a short space of about one inch. These long perforations are necessary because during rewind the paper is traveling over the trackerbar at about 40-50 feet per minute. Thirdly, while it still only takes the valves about 1/4 of a second to change back to the Locked Off state, it takes the Rewind Bellow a second or two to return to fully open, which again places the roll drive mechanism in the forward Play mode.


A nickelodeon 'build-up' is a regular player piano that has been converted into a nickelodeon. There are no records about when the first build-ups were produced, but it's relatively safe to say that they didn't come along until the 1950' when the Player Piano Company, in Wichita, KS, started producing lock-and-cancel valves of this variety. Since then, many thousands of nickelodeon build-ups have been produced by dozens of different people and companies.

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This page was last revised November 19, 2014 by John A. Tuttle, who Assumes No Liability
For The Accuracy or Validity of the Statements and/or Opinions
Expressed within the Pages of the Player-Care Domain.
Cartoon Graphics by E7 Style Graphics (Eric Styles)


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