Home Manuals Supplies Search Consult Contact Testing Service

Testing the Player Stack

Every Player Piano has a Stack (or Windchest) which houses the striker pneumatics (the small note bellows that move each individual note) and an associated valve (which senses the perforations on the roll and converts pulses of air into a switching action that opens and closes the valves. (detailed explanation - click here!)

Testing the Stack is fairly easy. There are a few tests which will help you determine the condition of the windchest (the valves and the striker pneumatics) relatively quickly. However, it's wise to insure that the screws which hold everything together are reasonably snug before you start the tests. If accessing the stack is a problem, at least tighten the screws that are accessible from the front and make a mental note that at least half that many screws are on the backside of the unit.

Twelve to Fifteen Inch Pounds is ALL You Need.

Begin Testing

Test One: One of the most comprehensive tests possible involves the use of a TEST ROLL. While the roll is running, write down every inconsistency that is heard or seen. (Some problems might be related to the piano action.) Keep this information for later use when working on the stack.

Test Two: Disconnect the main vacuum supply hose/s between the stack and the lower section at the lower section side. Usually, there will be only one large hose which connects to a vacuum flange on the upper left-hand side of the lower section. Some units have two main supply hoses-(see diagram). Next, connect a length of hose (about two feet) to the hose that was disconnected. In the case of two supply hoses, plug one or the other and test each side separately (see Split Stack).

WARNING: If it has been many years since the player was last used, it will be better to connect the hose to a medium* powered vacuum cleaner to suck out any debris that might be in the stack before sucking the tube by mouth. *Note: Medium means 15-20 inches of water vacuum.

Below is a video that shows how you can use your lungs to check various devices in a player piano.

Open the bleed (vacuum adjuster-- on the handle) All The Way.
Leave the Tracker Bar Uncovered and apply the vacuum intermittently.
Excessive Vacuum CAN DAMAGE the valves.

Once this has been done, cover the holes in the Tracker Bar with any type of tape, preferably one that won't leave any residue when you remove it. Note: In some players, the tracking mechanism and other peripheral devices might also be connected to the stack. If so, disconnect and plug the vacuum supply hose/s (tube/s) at each particular device. Now place your mouth over the main vacuum supply hose and inhale sharply (almost like gasping).

You should feel all of the note valves 'close' or seat almost instantly. In players with vertically mounted valves, the valves should be seated already and resistance should occur immediately. In units with horizontally mounted valves, it will take just a fraction of a second for the valves to seat. Once that happens, count the number of seconds it takes to fill your lungs with air.. In a perfect world, you will not be able to suck in any air. If that is the case, your stack is 100% air-tight. In the real world, there will be some amount of leakage. If the number of seconds exceeds 5 (five), the stack has fairly tight intake valves. If it exceeds 8 (eight) seconds, it's pretty tight. If it exceeds 12 (twelve) seconds, you're lucky. Your stack has very air-tight intake valves, gaskets and wood.

If you never reach the 5 (five) second mark but you do 'feel' the valves seat, the stack has a fair amount of leakage and further testing is required. If no resistance is felt, there is severe leakage. There are many possible explanations for severe leakage, ranging from very leaky valves to medium-to-large cracks in the windchest. Usually when there are one or more cracks in the chest, they can be heard as a 'sissing' sound. However, a leaky valve can also have the same general sound and only further testing can determine which problem exists.

Further Testing
Written by Craig Brougher

The philosophy behind this method of instruction is itemization and quick observation. You don't have to read the whole thing in order to get it. And it's separated into checks that stand on their own. I don't get into checking pumps, but here's a link to the pump tests -click here.

"If you think your antique player is leaking or not playing correctly, here are some tips and methods to check that won't take very long."


The player stack is the most important single component of the player piano because it has the most valves, and also because it plays the notes. It is the large "box" that usually sits above the keys in the majority of player pianos (there were a few older players whose stack was under the keybed).

If your player isn't playing or isn't playing very well, this will be one place to look. Naturally, we can always isolate it from the pumps to make sure that the problem isn't the pumps. But the first thing we should do is to test the pumping pressure when we operate the player by foot. This is done by laying masking tape over the tracker bar holes (that the roll glides over) and pumping the treadles manually (this is better than using the blank portion of a roll). If the pedals become very resistive and almost impossible to treadle, then you have a tight stack and the rest of the system is basically sound. But in most cases, when the valves have not been fully rebuilt, this pressure that you can feel under foot is less solid, and your pedals still move fairly easily. That means, your player leaks somewhere.

Assuming that you want to first see if you can fix your player yourself, here's the next things to do:

1. Remove the front boards of the piano and take a screwdriver to get down to the keys by removing the vertical front cover supports, music board, and nameboard. Now you can see the entire stack sitting in front of the piano action.

2. Disconnect the air motor hose (on the far treble end which drives the takeup spool and propels the roll, and cover its hose with duct tape. Treadle the pedals again and see what percent tighter your player appears to be. An air motor can take up to 25% of the air used at full speed. If things suddenly get pretty tight, then you had an air motor leak, usually in the supply hose. Use this link to Test the Air Motor.

3. When you are not satisfied, look further and you will usually see on many players, screws which tighten things down. If these screws obviously are clamping screws (as determined by a leather or cork gasket), then press in hard at each screw site while you take out the slack by turning in the screw and making it tight. If the screw is stripped, stop. Remove the screw, and fix the hole before continuing. But by pressing the cover hard, you will not over-tighten your screws by firming them down.

4. There are also other screws which tend to get loose as the gaskets shrink and expand over the years. For instance, some player stacks are made up of individual "shelves" clamped together with gaskets at their ends. If you have one of these, you will usually find either a large machine bolt at each end which draws them tight together, or long screws, often coming into the center shelf section from the top and bottom of the stack. At least, you can tighten the top pair without removing the stack, to see if it helps. Do this on each end. When you are satisfied that you've tightened all the clamp screws that you can get to, treadle the player once more.

Did your player respond a lot to your tightening it up? If it did, then that was at least a portion of your problem. Did the tightening "fix it?" If so, just remember, this was a "service problem" that many player manufacturers recommended that tuners always check on each time the player was tuned-- particularly if the customer complained about pumping too "easy." They mean, the pedals go down too easy, and sometimes they said, "it pumps too hard." Yes, that means they have to work too much. Any descriptive "too much" thing about the pedals means a leak.

Could you not find any clamping screws to tighten? That is also common, mostly in the Aeolian players, but all players which use cloth to tape the joints around, instead of gaskets to make them tight. Well, let's continue:

5. Since your leak could also be the pumping system, we will consider this separately, so if at this point you wish to check out your pumps, use the link right here to go to Testing The Pumps.

If you are getting enough vacuum to continue testing the stack, here's how to proceed:

6. Remove the chain temporarily that attaches the air motor to the transmission. Make a note of how the chain is made. You want to replace the chain on the sprockets later, so that the 2 loops of each link in the chain which connect to the adjacent link are facing outboard, toward you when the chain is running.

7. Put a QRS test roll on and spin the take-up spool by hand until you get to the note test. Make sure now that the reroll lever is in the play position, and start treadling as you move the roll. Pretty soon, a note should play in the bass. That's your first playing note. So keep treadling as you spool the paper by hand, noticing notes which may not play, or notes which play weakly, or which take lots of air. In all of this, make sure that your paper hole is directly over each hole in the tracker bar. Many a player doesn't play because they aren't tracking their roll well enough. Use this link to Test the Tracking Mechanism.

8. Using masking tape on the keys themselves, have a different mark for these 4 symptoms:

A. Note not playing or very weakly, but leaks a lot.
B. Note doesn't play at all but doesn't leak either.
C. Note goes down and stays down too long.
D. Note plays down as soon as vacuum is applied to the stack.

9. Use my ABCD system to mark your key tapes. There are many things that can be responsible, but assuming that your player used to play well, and now has a problem, here is the most likely problems:

A. Worn out note pneumatics or dry-rotted valve leather.
B. Tracker bar is clogged with a paper punching. Suck it out.
C. Valve's pouch bleed is clogged, or the tubing from the tracker bar has a tiny leak in it.
D. Tracker bar tubing has burst, or there is a leak at the input nipple.

Of course, there are other reasons. For instance, in players which have "primary valves" which look like little buttons popping up and down (just below the spool box, but above the main portion of the stack), you'll see that valve standing up if the problem is between the primary and the tracker bar. In that case, you usually have a leak to air at its pouch.

That would be air getting in all the time to inflate its pouch, like we said above. But it could also be some dirt or foreign object under the little button, holding it up. So check this, too. Primary valves are susceptible to dirt, and being also open to air, they tend to dry rot much more quickly than secondary valves, which are always enclosed.

These are stack checks that you can make. Repairing a pneumatic player by disassembling it is another matter, and requires a great deal of knowledge and experience. If you decide you are more than capable of doing it, we'd just like to throw this in for what it's worth: Plan on doing over as many times as necessary, in order to get it right! That implies that you use materials and glues that will allow you to access what you have already done, because it is a sure bet that you will not do everything right the first time, as careful as you may be, and as many notes as you may take. Players are very reliable, once fixed right. But they are both an art and a science, and require a certain "touch" and understanding that few organ builders or engineers know, by nature. Try it and see if this isn't a pretty accurate statement.

Craig Brougher

The Tracker Mechanism is the device that keeps the holes in the paper roll lined up with the holes in the tracker bar over which the rolls pass.

Peripheral Devices

Peripheral devices are any devices that are not essential to the operation of the player piano. Most typically they include but are not limited to the Bass and/or Treble Soft Pneumatics (and associated valves) and the Auto-Sustain Device.

Inch Pounds

Inch-Pounds the product of force and radial distance. For example, 12 inch pounds is 1 lb of force applied at 12 inches radius or 2 lb applied at 6 inches or 3 lb applied at 4 inches. So you see, it's not very much force.

A Split Stack

As the name implies, a stack with two main vacuum supply hoses is usually split into two equal parts. Typically, these parts are referred to as the Bass Side and the Treble Side. In a stack that is truly split, there is a physical partition between the two sides. However, there are some units that have two main vacuum supply hoses that are NOT split. Determining whether the stack is truly split can be easily accomplished by sucking on one hose and listening to the other. If you can hear (or feel) the rushing air, the stack is not split. Return to above

Removing the Stack

Although there are one or two extremely common points where the stack connects to the piano, the best rule of thumb is 'when the correct screws have been removed, the stack will be easy to remove'.

1) Starting at the top of the stack, remove the screw that connects the support arm (connected to the top of the spoolbox) to the plate (or harp).

2) Disconnect all metal linkage to the transmission and the tempo indicator.

These are normally located on the right-hand side of the stack. By moving the tempo and play/reroll levers one at a time, the point where these linkages connect to the upper section can usually be seen with the naked eye. Most typically, there is one leather nut holding one piece of linkage to its mating piece. However, there are models where they used machine screws. In some modern units, the function and its associated lever are both a part of the upper section. In that case, there is no need to disconnect the lever from the device.

3) Disconnect all rubber or neoprene tubing.

One of the most obvious tubes that must be disconnected is the air-motor supply tube. It can be on the right or left of the upper section but it will be connected to the air-motor. If the tubing is very brittle, break it a few inches from the flange (or nipple). Quite often, attempting to break the tube at the fitting will damage the fitting.

Then locate and remove any smaller tubing on the left side. Typically, the Auto-Sustain tube runs out the left side. Some players also have a Play/Reroll valve in the upper section, and the tube leading to it must also be removed.

4) Locate and remove the Stack Mounting Screws.

Locating the mounting screws is usually pretty easy. First off, they're usually fairly good size screws with 3/8"-5/8" heads. Second, they're most often found at each end of the stack. I've never seen more than two screws on the right side unless the unit has a split-stack. Most often, there is only one screw on the right. On the left, there are usually three or four screws. That's because the vacuum port is usually on the left, and there is a gasket between the mounting block and the stack. So those screws actually serve a dual purpose. Mounting and sealing. Some units only have mounting brackets on each end with one screw each. Units like that are connected directly to the lower section with a piece of fairly large tubing (7/8"-1-1/2" ID). And there are a couple of units that have a mounting bracket near the center of the stack, which connects to the keybed.

5) Gently try to move the Stack.

Once you feel that everything's been disconnected, gently try to move one end towards you about one inch. If you encounter any resistance, stop and look. Find out what's not letting go. Then do the same on the other side. Once the stack has cleared the piano action, it can be lifted up and out of the piano. One fairly strong lifting point is the tracker bar. If possible, one person on each end is safest.

Next Installment... Regulating the Air-Motor Governor

The Piano Action

Here at Player-Care, no attempt is ever made to explain anything about the piano action. There are literally hundreds of websites that deal with regular pianos. Simply do a web search for 'piano action'.(back to top)

Player Piano Reference Materials - Click Here

We Gladly Accept These Cards
Discover, VISA, MasterCard

back to top..To The Top of this Page . . . . . . . . . . . back to index ..To The HOME Page

This page was last revised December 6, 2020 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 T Styles)

Since "Player-Care" is an internet business, I prefer that we correspond via E-Mail (click here to fill out the 'Request Form'). However, if I'm not in the middle of some other activity, you can reach me at 732-840-8787. But please understand that during the hours from 8AM-5PM EST (Mon-Sat), I'm generally quite busy. So, I probably won't answer the phone. If you get the answering machine, please leave a detailed message stating the reason for your call. Also, repeat your name and phone number clearly and distinctly. By necessity, I prioritize everything in my life. And, if you call and just leave your name and number, and ask me to call you back, it might be a day or two before I return your call. Why? Because I don't know why you want me to call and I might not be prepared to assist you in an effective and efficient manner. If you leave me an E-Mail address (which I prefer), spell it out phonetically. The more you do to help me, the more I can help you in return. Don't rush. You have four minutes to record your message.

Grand 16 IconGrand 32 Icon

407 19th Ave, Brick, NJ, 08724
Phone Number 732-840-8787
(Voicemail Only, No Texts)
Upright 32 IconUpright 16 Icon

Google Adsense Ad

SSL Certificates