BF Sturtevant Co. v. Massachusetts Hair & Felt Co.

Decision Date21 November 1941
Docket NumberNo. 3644,3645.,3644
PartiesB. F. STURTEVANT CO. v. MASSACHUSETTS HAIR & FELT CO. MASSACHUSETTS HAIR & FELT CO. v. B. F. STURTEVANT CO.
CourtU.S. Court of Appeals — First Circuit

Harry Dexter Peck, of Providence, R. I., and Melvin R. Jenney, of Boston, Mass., for B. F. Sturtevant Co.

Ralph L. Chappell, of Kalamazoo, Mich. (Robert J. Keating and Roberts, Cushman & Woodberry, all of Boston, Mass., and Earl & Chappell, of Kalamazoo, Mich., on brief), for Massachusetts, Hair & Felt Co.

Before MAGRUDER, MAHONEY, and WOODBURY, Circuit Judges.

WOODBURY, Circuit Judge.

These are cross-appeals from a final decree of the District Court confirming the report of a master in a patent suit.

The B. F. Sturtevant Company, which will be referred to hereafter as the plaintiff, is the assignee and present owner of two letters patent, one granted on February 23, 1932, and the other on January 29, 1935, to one Harold F. Hagen as its assignor. These patents are numbered 1,846,863 and 1,989,413 and are respectively for "Improvement in Fans and Methods of Operating the Same" and for "Improvement in Centrifugal Fans." Hereinafter they will be referred to as Hagen's first and Hagen's second patent.

On May 18, 1936, the plaintiff filed a bill of complaint in the District Court charging the Massachusetts Hair & Felt Company with infringing both of these patents by using in its plant at Peabody, Massachusetts, a so called Vortex control fan made by the Clarage Fan Company of Kalamazoo, Michigan. The Clarage Fan Company openly assumed and conducted the defense of this suit and, unless otherwise noted, will be referred to in this opinion as the defendant.

In issue are claims 1 and 2 of the first Hagen patent and all four claims of the second Hagen patent.

The master, after full hearing, found, with respect to the first patent, that claim 1 was invalid both for anticipation and for absence of patentable invention; that claim 2 was valid; that both claims were infringed; and that the plaintiff had not been guilty of laches. With respect to the second Hagen patent he found that although none of its claims were anticipated, all were invalid for absence of patentable invention; and that all had been infringed. The District Court in its final decree adopted the findings of fact contained in the master's report as its own and confirmed that report. The plaintiff appeals from so much of the final decree "as dismisses the bill of complaint herein as to claim 1 of Letters Patent No. 1,846,863 and as to Letters Patent No. 1,989,413." The defendant appeals from the portions of that decree "which hold claim 2 of patent No. 1,846,863 valid and infringed."

In order to understand the questions of mechanics, physics and law raised by these appeals, it will be necessary to consider at the outset the construction, function and uses in industry of centrifugal fans or blowers. These machines, in their simplest form, consist of a wheel, called a rotor or impeller, attached to a shaft for rotation inside a scroll-shaped casing. Rigidly fastened around the circumference of this wheel are a series of identical blades or paddles which are usually curved backward away from the direction of rotation. In each side of the casing are circular openings around the shaft upon which the rotor is mounted. These openings are concentric with the rotor shaft and are called the air inlets, or eyes, because through them enters the air or other gas to be moved by the fan. In order not to obstruct the eyes, the bearings in which the impeller shaft is journaled are generally set some distance out from the casing.

Fans of this sort act upon the air, predominantly by centrifugal force, to increase its pressure and deliver it through the outlet which is the straight portion of the scroll-shaped casing. They are used for various purposes, including ventilation and furnace draft, and are of two general types. When such a fan is located at the entrance end of a system, that is, when it takes air directly from the atmosphere and forces it under pressure into the system, it is called a forced draft fan. When it is located near the delivery end of the system, that is, when it draws air out of the system and discharges it into the atmosphere, it is called an induced draft fan. Fans of either sort as used commercially are frequently of substantial size, the rotor or impeller in some cases being eight or more feet in diameter.

As a centrifugal fan operates and forces air through its outlet, atmospheric pressure forces air into the fan through its inlets. This air, if the inlets are open and unobstructed, enters axially, that is, parallel to the shaft upon which the rotor is mounted, but in order to replace the air being forced out, it, when inside the casing, turns at right angles to its path at entry and moves radially outward to the blades of the impeller. As the master describes it:

"Air enters the eye of the impeller (sic. casing) in a generally axial direction, and if it were to continue to flow entirely axially, it would never reach the fan blades and no work would be done. But as the air passes into the fan it moves radially toward the blades, and the air has both an axial component and a radial component, one perpendicular to the other."

The output of a fan, which the master defines as "the product of the pressure and the volume of air delivered", depends upon the amount of work done on the air in the fan by the blades of the impeller, and the amount of this work depends upon the speed relative to the entering air at which the impeller is revolved. In industry it is frequently desirable if not essential to vary this output, that is, to vary the amount of air being forced or drawn through a system, and "It is with this matter of control of fan operation to meet changing requirements of the same system, that the Hagen patents are concerned."1

Obviously a reduction of the speed of the rotor of a fan will reduce the speed of its blades relative to the entering air and thus "reduce the pressure, with accompanying reduction of volume delivered", but although this, so far as the fan itself is concerned, is the best and most efficient way yet devised of controlling its output, there are distinct disadvantages accompanying the use of variable speed control in modern industrial plants.

"If the fan is driven by a steam turbine, variable speed can be easily and efficiently effected, and prior to 1922 or 1923, steam turbines were commonly so used. About that time plant designers introduced what is known as the regenerating cycle, which involved using the steam for heating the feed water, and the use of turbines for fan drive has, since then, largely gone out.

"With direct current (electric) motors, speed control can be accomplished with efficiency, although the motor control may have to be supplemented by some damper control to give control between the fixed steps of speed provided by the motor.

"But direct current is little used in industry, except in a few places such as Detroit. And with alternating current in use most everywhere, difficulties are encountered in providing for variable speed control. Such control with an alternating current motor involves high initial cost, and considerable space for large banks of resistors. What is known as a slip-ring alternating current motor can be used, but its efficiency falls off rapidly as speed is reduced. As with direct current motors, it is necessary to supplement the motor control with damper control, to provide control between the steps provided by the motor."

The damper referred to by the master in the above quotation is defined by him as "a restriction placed in the air passage." In the fan art its action is commonly termed "throttling." This method of control is "accompanied by a waste of a part of the power developed by the fan, which is used in overcoming the added resistance imposed by the damper." Because it is wasteful, throttling, except in conjunction with speed control, is seldom used except in small installations when waste is of no great consequence.

The Hagen patents pertain to a third method of regulating the output of a fan called "vane control." This method, as the name implies, "involves controlling fan operation to meet changes in system requirements by the use of adjustable vanes at the inlet or eye of the fan, operating to impart to the entering air a velocity of spin in the direction of blade rotation, by which, at constant speed, the work done on the air by the fan can be varied, with a corresponding variation in power necessary to drive the fan."

In further detail the master describes the essential principle of operation of vane control as follows:

"In an ordinary fan in which the air enters through an open unobstructed eye, the air will approach the rotor blades in a radial direction without any appreciable spin or whirl. And the speed of the blades relative to the air is the actual speed of the blades. The rotor will exert considerable force in changing the direction of flow and in impelling the air in the direction of its rotation, such work being reflected in an increase in pressure in the air as it leaves the rotor.

"A rotor cannot impart as much energy to a stream flowing in the direction of rotation of the rotor as it can to fluid which is not already flowing in that direction. If the air, by some means or other, when it enters the fan, is already whirling or rotating in the direction of fan rotation, and at the same speed, then the rotor blades can apply no force to it, and there is no increase in pressure in the air. No work will be done by the fan, and the power necessary to operate the fan is at a minimum. If the air is spinning in the direction of fan rotation, but at a speed less than that of the fan, then the fan will exert some force on the air to speed it up, and there will be an increase in pressure imparted to the...

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