DUO-ART CROSS VALVES, AGAIN?
You know, This subject keeps popping up, again and again, like a cork. The reason is because rebuilders too often do not understand the pneumatic principle involved, but after they have restored a set of old cross valves, they work. So their conclusion is obviously that there was nothing wrong with cross valves, and anybody who says differently just doesn’t know what he’s talking about.
In the first place, Aeolian themselves admitted having some terrible experiences with cross valves, and in the worst of places– at universities and music conservatories across the country, where Duo-Art pianos were used heavily and moved often. When a heavily used Duo-Art was moved, invariably it never played the same, again. That’s because of the “criss-cross”impression made permanent in the valve leather by having been “sucked down” against such a seat for so many times. Then when the piano was transferred to other quarters and set up, as the schools grew and reorganized, expanded, moved to other quarters, etc. those Duo-Arts also got moved around, and never played well, since. So they were discounted as “worn-out,” when actually, their Ampico counterparts were playing as well as ever. The reason was simple, the moving jiggled the valves and they rotated a little as they were trucked or moved. The result is clearly seen in a picture included with this article.
Notice how the criss-cross pattern has been “jogged” a little, and a new pattern made, superimposed over the old one? The black stuff that allows you to see that rotation has occurred is carbon dust, prevalent in all old buildings of the 20's and 30's when they burned coal for heat. The valve at the bottom left shows the outside valve with about 12 lobes (hard to see, here). This leather was still in perfect condition, but it was all removed, along with the cross valve plates, and restored properly. By the way, the performance was actually improved beyond original capability when brand new.
I cannot stress this fact enough-- that no rebuilder will ever have any problems with cross valves, guaranteed. How much more obvious can it be? Only the OWNER will have the problems, and those will be 5-10 years down the road! By that time, where will the cross-valve rebuilder be? I guarantee you, he will not be at your side, ready to take full responsibility for your problem at his expense. This is my main objection. They don’t hold up.
Now in the MMD issue 05.04.22 article, subject Duo-Art Cross Valves, 04/22/05, we read a few things that I would also like to take to task. I have done an extensive study of cross valves, and there is absolutely nothing in the article which is fully correct. So I will quote from the article, and then I will add my comment, below the quote. Here is his first quote.
“However, I have restored hundreds or thousands of cross valves and had no problems. There is an issue with replacing the valve seats that many do not understand and that it is the relationship between the air flow and "pluck" of the valve. Pluck is the resistance to activation from the "off" (or closed) position.
“At the reduced valve gaps utilized by player stack valves, flow becomes primarily dependent on orifice perimeter. Under these conditions, an orifice with a multi-faceted perimeter (such as a star or a cross) will have greater flow than a circular orifice. At such small valve travel (gap), orifice area is less important to flow than orifice perimeter.”
Let’s take the last paragraph first. This is a physical impossibility. “Orifice perimeter is more important to air flow than area?” Well, let’s exaggerate the situation so you can see for yourself if that’s a law or not. Suppose you had a slit .00001" wide and 100 inches long. Now, what is the perimeter? Well, it is 200.00002 inches long. But what is the open area? I mean, how much room is allowed for the air to blow through? The answer is 1/10,000 of a square inch! That’s far less than a pouch bleed, but look at the perimeter of the hole. Enormous. So much for “perimeter.”
I built a demonstrator to show the effectiveness of a cross valve, years ago, at an AMICA meeting in St. Louis. It was a captured poppet with a cross valve on one side and a replacement round valve on the other. The travel was the normal .035." The valve chamber was tubed to a large, heavily sprung reservoir bellows, which was fully depressed with the foot and released. When the poppet was pressed over, closing the ½" round hole (replacement valve plate), The bellows relaxed open through the cross valve plate. It did so about 25% slower, and with a decided loud hiss, besides. When the poppet was switched over, pressing against the cross valve plate and closing it, while opening the round hole plate, the bellows opened much faster and with no discernable hissing sound at all. Granted, the large bellows exaggerated the efficiency of the valve plates, but that was necessary, so that it could be demonstrated to all in the room, without any variance of opinion.
Regarding so-called “PLUCK” force. Let me clarify that for you, too. The cross valves all used small pouches and large diameter valves. This only worked with small pouches because the valve plate was a cross-shape, and as soon as one corner of the cross was even slightly relieved by upward pouch pressure, all the suction disappeared and the valve easily actuated. That happened because no valve lifts straight and flat, so it was a cinch that the valve could not ever raise straight up. However, if the valve plate had a ½" dia. hole instead, with that same pouch, then it would have to raise all at once, and those small pouches just didn’t have enough OOMPH to do it quite as quickly as required by fast repeating notes. The author is correct.
So what’s the solution? How could anybody make these oversize valves work fast with an undersized pouch against ½" diameter holes which are far more efficient?
Simple. If you glued a new full diameter, .065 thick valve leather over that, you have made exactly the mistake he admits to having made, here. Remember, those poppets had to be large in order to cover the ends of the cross valve pattern, so they are far too large when covering a ½" hole, and the suction is expressed as oz/sq. In. Over the entire surface, not just the active hole area. But when you substitute a ½" diameter valve hole for a large cross valve, then would it not stand to reason to use a smaller leather on the poppet? Size it accordingly. It’s just a matter of thinking what you’re doing, first.
“It is true that Aeolian went to the round valve plate, but stayed with the cross valve in the
Steinway and high end pianos. The less expensive pianos used the round plates and there were
different sizes of them depending on the model and year. Also, keep in mind that when the valve
plates got smaller, so did the valve itself. It is a delicate balancing act.
Let’s take the last statement first. IF you could buy industrial tanned, pre-stretched
leather with a satin suede nap, .055-,065 thick, then I agree with that last statement.
But that doesn’t mean the cross valve functioned as well as a round valve, either! It
never did. Since you cannot buy industrially staked, pre-stretched satin suede leather,
then I disagree with the statement. The only leather generally available today is
garment leather, which is far softer than what Aeolian used and makes a soft, cushy
impression very quickly. It also takes a permanent set faster, and would give the old
cross valve owner no end of trouble, promptly.
Let’s take the last statement first. IF you could buy industrial tanned, pre-stretched leather with a satin suede nap, .055-,065 thick, then I agree with that last statement. But that doesn’t mean the cross valve functioned as well as a round valve, either! It never did. Since you cannot buy industrially staked, pre-stretched satin suede leather, then I disagree with the statement. The only leather generally available today is garment leather, which is far softer than what Aeolian used and makes a soft, cushy impression very quickly. It also takes a permanent set faster, and would give the old cross valve owner no end of trouble, promptly.
Now let us ask ourselves, “Why did Aeolian go with the round valve plate in later model pianos, but (supposedly) stayed with the cross valve plate in the Steinway and “high end” pianos? Hmm. The implication is that lesser pianos deserved a lesser valve design, so in order to keep Steinway the top of the line, we had to change all the other brands to an “inferior” round valve. Surely the author didn’t mean to imply this! The suggestion should have been noticed and clarified, lest we all get the wrong impression (or unless that’s the impression he intended to leave. I don’t know).
In the first place, all later model Steinway Duo-Arts used the round valves, so he is wrong. So did all Ampicos and Weltes and their top of the line, high end pianos, including Hamburg Steinways, from the very first reproducing piano models, through to the very last ones.
I had a bet with a fellow rebuilder, why so many Steinways ended up with cross valves. It went like this:
Aeolian miscalculated how many Steinways they would sell. They were manufacturing thousands of player stacks for the model X and O Steinways, in advance of orders, which they were sure would ensue, just as soon as these new instruments hit the stores. When the Steinways weren’t selling as fast as they thought they would, they didn’t cut back production, because Steinway assured them that the basic scale instrument would always be available, hence the room required for the stack. So to Aeolian, it was just a matter of time and acceptance, so they kept manufacturing them in anticipation of increased sales. When sales did increase in the late 20's, they wrote a contract with Steinway for 50,000 specially made pianos. They had stacks and many of these parts ready to outfit those instruments, anyway, so Aeolian felt they were ahead of the game. But when the depression hit, Aeolian would have been ruined, had Steinway not let them out of the contract (which also benefitted Steinway, as well). All the time, Aeolian had long ago stopped making cross valves and was only making round valves, but each Steinway ordered received an older model stack from the warehouse.
We attended the Minneapolis/St. Paul Convention that year and my friend Bill knew a fellow there who could put this question to bed once and for all, and so invited me over to listen. John was a friend of Bill’s, and a close friend of a few former Aeolian employees who had already talked to him about many incidences like this, and lo and behold, John verified my story. So the reason Steinways had cross valves in their players was NOT because of its superiority, but it’s anticipatory sales convenience. They had already been assembled, tested, and laid up for the next Steinways to be sent to dealers.
As far as all the other aspects of a cross valve, well, they were inferior in all respects, including noise and air flow. A ½" round hole was totally superior by actual test, and it also operates faster with the original Duo-Art pouch than the cross valve does, as long as you remember not to cover the entire diameter of the inside valve poppet with the leather. When using the round hole, you also need less valve travel, hence valve action can be a little quicker (theoretically but not measured) on the return.
Another important trick in valve leather is this– do not use thick, heavy leather. Instead, use a hard surfaced, thin suede valve leather of the correct diameter, so that the valve leather doesn’t conform to the slightly convex stamping of the replacement valve. You want it to touch mainly around the hole perimeter, and touch as little margin of the metal as practical. The replacement valves are not flat bottomed, but slightly dished down, and that can create a problem, unless you know better.
If any reader is interested in reading my research on this valve in 1997, he is invited to check out these links.
These will give you all the data you probably need to decide. And while you’re doing that, I might also add that Aeolian themselves admitted that cross valves turned out to be a regular nightmare. Someone at Aeolian even tried to redesign it so that the stem was pinched flat at the top end, and was guided by a fiber guide with a slot instead of a round hole. This variation was actually found in a piano in New York state by Robert Streicher. It didn’t work, because the slot still allowed for about 5 degrees of rotation, and frankly, that was about 10 degrees too much. The answer was obviously to redesign the valve, but it was just too late for the many anticipated Steinways.
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