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As they relate to Player Pianos Like compressed air, vacuum puts the atmosphere to work. But unlike compressed air, vacuum uses the surrounding atmosphere to create the work force.
Evacuating air from a closed volume develops a pressure differential between the volume and the
surrounding atmosphere. If this closed volume is bound by the surface of a vacuum cup and a
workpiece, atmospheric pressure will press the two objects together. The amount of holding force
depends on the surface area shared by the two objects and the vacuum level.
One inch of water equals 0.036127 psi Hi John, since we use inches of water column , 1 pound pressure will raise a column of water 27.6799048425 inches. The table Jody suggested did not seem to answer your question. Here are the conversion factors in both directions: Pressure in psi X 27.6778 = Pressure in Inches of water. Pressure in Inches of water X .03613 = Pressure in psi
Typical vacuum cleaner reduces air pressure by about 20% In 1654, 1. Otto von Guericke invented the first vacuum pump[36] and conducted his famous Magdeburg hemispheres experiment, showing that teams of horses could not separate two hemispheres from which the air had been partially evacuated. Robert Boyle improved Guericke's design and with the help of Robert Hooke further developed vacuum pump technology. Thereafter, research into the partial vacuum lapsed until 1850 when August Toepler invented the Toepler Pump and Heinrich Geissler invented the mercury displacement pump in 1855, achieving a partial vacuum of about 10 Pa (0.1 Torr). A number of electrical properties become observable at this vacuum level, which renewed interest in further research. How many inches mercury in one inch of water? The answer is 0.0735559124637.
Hi John, since we use inches of water column , 1 pound pressure will raise a column of water 27 inches.
From: rumpf.paul@yahoo.com.geentroep (Paul Rumpf) To: rolls-1201@mmdigest.com Date: Fri, 24 May 2013 04:00:29 -0700 (PDT) Subject: Player Piano Valve Design Parameters John Tuttle asks some questions in 130520 MMDigest for which there are simple answers and complex answers. Taking the questions in turn: > > 1. Does the square area of the pouch have to be bigger than the > > square area of the valve seat? The simple answer is "yes". The reason for this is that the pouch at rest has to lift the weight of the valve stem plus the weight of the vacuum force which forces the valve to shut tightly. Five inches of water gauge is a pressure of 0.185 psi. Consider the pouch as a piston and its lifting force is, for a one inch diameter pouch, Force = pi/4 x 1 x1 x 0.185 = 0.145 lb.f = 2.35 ounce force The weight of a 'Standard' valve stem, etc., is about 6 grams or 0.2 ounce. The valve disc diameter is about 0.67 inch. The downward force due to the valve disc is: = pi/4 x 0.67 x 0.67 x 0.185 = 0.065 lb.f = 1.04 ounce force. So the opening force is 2.35 ounce and the force plus mass of the valve is 1.04 plus 0.2 ounce force; = 1.24 ounce force. If the valve disc was the same diameter as the pouch, then the pouch could not lift the valve. > > 2. In terms of physical size, is there a finite point at which > > a pouch and valve are so big that the pressure of the atmosphere > > is not great enough to activate the valve? The simple answer is the atmospheric pressure has nothing to do with the lifting of the valve. The valve lifts because of the pressure difference between each side of the pouch. See below: 3 and 4 > > 3. What is the exact ratio between the size of the bleed and the size > > of the hole in the trackerbar at which the note will fail to activate > > when the trackerbar hole is open to the atmosphere? The simple answer is "there is no simple answer." The tracker bar is connected to the pouch through a long tube. Outside the tracker bar is atmospheric pressure. When the tracker bar is open, air flows through the port and the tube through the bleed to the vacuum supply. There is a pressure gradient along this tube, but ideally this pressure gradient is small, so that under the pouch, the air pressure is close to atmospheric pressure. It is the flow of air through the bleed, which gives rise to an air flow which increases the pressure gradient along the tube. This results in the air pressure under the pouch falling from atmospheric pressure, to a pressure closer to the vacuum level above the pouch. This reduction in pressure difference across the pouch reduces the force development potential of the pouch. From this point of view a small bleed is to be preferred. > > 4. What is the exact ratio between the size of the bleed and the > > size of the hole in the trackerbar at which the note will fail to > > turn 'off' as fast as it turns 'on'? The simple answer is "there is no simple answer." The bleed must remove the atmospheric air under the pouch when the tracker hole is covered again, before the valve can shut off. For reasons of closing speed, the bleed should be large to extract the air more quickly, but in question 3 we showed the bleed should be small. So the bleed size is a compromise. The obvious example of bleed sizes, is the Ampico model "B" where there is a small bleed for turning the valve on and holding it on, and a larger bleed for exhausting the pouch when the valve turns off. > > 5. Are there formulas that a person without a degree in physics can > > understand that can be used to accurately determine things like the > > optimum size of a pouch, valve, a bleed, and striker pneumatic? Or > > was it all done by trial-and-error? The simple answer is that most things can be understood through quite simple explanations but design matters involve more rigour. Bleed design is a compromise and is affected particularly by pouch material selection and its leakage stability over time. In my paper about force development (in the MMD Archives) I consider such matters as force development in pneumatic motors. Such work generally comes along after the initial experimentation has confirmed an approach, but quantifying an engineering systems through mathematical models is invariably necessary for product optimisation. See http://www.mmdigest.com/Gallery/Tech/rumpf_1.doc I guess there was some guess work, but the anecdotal evidence relating to the story of Dr. Hickman's arrival at the American Piano Company, shows how mathematical modelling is an important part of all product design and manufacturing. Paul Rumpf |
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