Lamson Co. v. E. T. Slattery Co.

• Decision Date: 17 March 1924
• Docket Number: 1831.
• Citation: 296 F. 724
• Parties: LAMSON CO. v. E.T. SLATTERY CO.
• Court: U.S. District Court — District of Massachusetts

296 F. 724

LAMSON CO. v. E.T. SLATTERY CO.

No. 1831.

United States District Court, D. Massachusetts.

March 17, 1924

Robert Cushman and Roberts, Roberts & Cushman, all of Boston, Mass for plaintiff.

George A. Sweetser, of Boston, Mass., and W. P. Preble, of New York City, for defendant.

MORTON District Judge.

This is a suit for the infringement of patent No. 968,576 to Charles R. Libby, dated August 30, 1910, for improvement in pneumatic dispatch tube apparatus. The bill alleges that all of the claims are infringed. The defense principally relied upon is noninfringement.

The Libby patent relates to vacuum cash carrier systems which are in common use in large shops and in many other places. Such systems, of the type here involved, consist essentially of a tube open at one end to the air and connected at the other end to an exhausting pump, and of cylindrical carriers adapted to fit like a piston in the tube. When such carrier is inserted at the open end of the tube, it is pushed forward by the pressure of the atmosphere behind it against the partial vacuum in front of it. At the discharging point a fixture, which it is unnecessary to describe, is interposed in the tube so that the carrier is shot out into the proper place.

When such systems were first installed the intake end of the tube was left open, and a continuous current of air to the full capacity of the tube was constantly sucked through it. As the tubes were two inches or more in diameter, this required a large amount of air to be handled, and the continuous expenditure, in large installations, of about one-half horse power per tube. As any given tube would be in actual use only a small part of the time, there was a great waste of power.

Libby solved this difficulty by interposing in the suction part of the tube, nearer the exhausting machinery than the carrier would go, a valve which normally closed it, but which opened automatically whenever a carrier was introduced into the tube. This valve prevented the needless suction of air when the tube was not in use. Such an arrangement saves, on the testimony before me, rather more than half the power otherwise required. The underlying idea of the Libby patent viz. a valve in the tube which is normally closed thereby preventing the wasteful suction of air and which is opened by the momentary change of vacuum or air current caused by the introduction of a carrier, and closes after the carrier has left the system, was old, being clearly shown in the Bavier &amp Hawks patent, dated September 18, 1900. That patent, however, relates to a closed system, and could not be transferred to an open one without basic, and perhaps inventive, rearrangement. Open systems have advantages over closed ones; and the Libby patent shows the first tube valve actuated pneumatically by the introduction of a carrier adapted for use in such systems. To this extent it is a pioneer patent. The same result had been secured in other ways by electrical apparatus.

The Libby mechanism consists essentially of a clapper valve hinged at its lower edge and normally held in a closed position by a spring. When shut it completely closes the tube. It is controlled by a diaphragm placed in a closed chamber on the suction side of it. A small by-pass, the capacity of which can be accurately regulated, connects the part of the chamber behind the diaphragm with the tube. Normally the pressure on both sides of the diaphragm is equalized through this by-pass, being the same as that in the tube; and the spring keeps the valve closed. The action of the diaphragm is controlled by a small valve (which I shall refer to as the controlling valve) which, when opened, allows the full pressure of the atmosphere to act on the back of the diaphragm. This pressure is sufficient to overcome both the spring which holds the principal valve shut and the reduced air pressure in the tube, and to open the valve, thereby permitting a full draft of air through the tube.

The mechanism by which the controlling valve is actuated consists of a second diaphragm set into a pipe by-pass which opens into the tube above and below the principal valve. This by-pass brings upon the back of the controller diaphragm the pressure in the tube, i.e., about one pound of vacuum. The other side of this diaphragm is open to the atmosphere except when the principal valve is open. In order to prevent the pressure of the atmosphere from forcing the diaphragm against the vacuum, thereby keeping the controlling valve always open, the stem of the controlling valve is pressed shut by an adjusting spring, the tension of which is just sufficient to overcome the difference in pressure on the two sides of the diaphragm and to keep the controlling valve seated. This diaphragm and the controlling valve which it actuates may be regarded as a balanced valve, having on one side the pressure of the atmosphere, and on the other a reduced atmospheric pressure supplemented by the pressure of the spring. The exhausting machinery is constantly drawing a slight amount of air through the conveyor tube via the pipe by-pass.

The introduction of a carrier into the mouth of the tube stops the inflow of air. This causes an increase of vacuum in the tube and by-pass, and on the diaphragm of the controlling valve; it upsets the balance of that valve and allows the pressure of the atmosphere to force the valve open. The opening of the controlling valve causes, as has been described, the opening of the principal valve and allows a full current of air to be drawn through the transmitting tube thereby moving the carrier.

The closing mechanism: Once open, the principal valve would, if there were no further mechanism, stay open, either permanently or at any...