US503231A - drewett - Google Patents

Description

(No Model.)

2 Shqsets-Sheet 1.

W. A. DREWETT. DIRECT AUTING ENGINE.

Patented Aug. 15, 1 893.

attomzw I UNITED STATES PATENT OFFICE.

WILLIAM A. DREWETT, OF BROOKLYN, NEWYORK, ASSIGNOR TO MARSHALL T-. DAVIDSON, OF SAME PLACE.

DIRECT-ACTING ENGINE.

SPEGIFIGATION forming part of Letters Patent No. 503,231, dated August 15, 1893. Application filed October 11, 1892. Serial Ha t 8,507. (No model.)

To all whom it may concern:

Be it known that I, WILLIAM A. DREWETT,

Brooklyn, Kings county, New York, have in vented certainnew and useful Improvements in Direct-Acting Steam-Engines, of which the following is a specification.

My invention relates to direct acting steam engines, and more especially to that class of engines adapted for operating pumps, and it has for its object to provide means whereby the valve-pistons of the engine shall be more perfectly balanced, and can consequently be operated more easily and readily, and to these ends my invention consists in the features of construction and arrangement substantially as hereinafter pointed out.

' Referring to the accompanying drawings, Figure 1, is a longitudinal vertical section through the steam cylinder and valve mechanism. Fig. 2, is a vertical transverse section on the line 22 Fig. 1; and Fig. 3, is a horizontal section through the valve mechanism on the line 3-3 Fig. 1.

My invention relates especially to .direct acting engines in which is used what is known as the Davidson steam valve, and I have illustrated my invention in connection with sufficient of the Davidson steam pump and pumping engine to enable those skilled in the art 'to understand its construction and operation.

This valve is arranged to be oscillated mechanically, to then be reciprocated or moved longitudinally a sufficient distance to close in order that its construction may be better understood, I will describe briefly the general characteristics of the Davidson valve and engine.

The steam cylinder A, which is shown only partially, is provided with the piston P, the

'piston rod P, which is connected with the pumping apparatus not shown herein. Mounted on the steam cylinder is the steam chest 0, receiving steam from the pipe 13, and containing a valve D. This valve is shown as a D-shaped valve having pistons E, E, which may be formed integral with the valve or connected thereto in any desired manner. The under side of the valve is recessed as at f, to form an exhaust port communicating with the main exhaust passage F formed in the casting of the steam chest, and the spaces g, 9 between the ends of the valve and the pistons operate as ports to communicate with the main piston ports G, G of the steam cylinder. The steam chestis also provided with valve piston ports e, e which extend longitudinally of the steam chest from a point about the center thereof to near the opposite ends, and these valve piston ports are arranged on opposite sides of the lower portion of the steam chest as seen in Figs. 2 and 3, and have openings communicating with the chest at each end. The arrangement of these ports is best indicated in dotted lines in Fig. 3, and it will be seen that the valve is provided with ports or recesses d, d, in its sides which can be brought in coincidence with the openings of the valve piston ports.

In the Davidson engine the valve D, is provided with a pin H, which extends into the exhaust port F, and also mounted in the exhaust port is a cam I, to which is connected the arm I, and this in turn is connected by suitable mechanism, as a link 1 to the piston rod, so that as the piston moves, the valve D, is mechanically oscillated to open and close the valve piston ports, and is partly thrown longitudinally so as to produce a closure of the main piston ports, and the further longitudinal movement of the valve in the steam chest is accomplished by the steam passing through the ports e, e, and acting on the pistons. Thus it will be seen that the valve has first an oscillating movement produced mechanically, then a longitudinal or reciprocating movement also produced mechanically, and finally a further longitudinal movement produced by steam pressure. This operation will be readily understood by referring to Fig. 1, wherein the parts are shown with the main piston port G, as partially open to the passage of steam to the steam cylinder, while the port G, is partially open to exhaust from the cylinder, and the piston is shown in the position near to the end of its stroke, and the cam I, has oscillated the valve and moved it longitudinally, so as to nearly close the steam passages, and, as the piston advances farther, these passages will be completely closed by the mechanical action of the cam. The oscillation of the valve has in the meantime opened the valve piston port 6, so that the steam will pass behind the valve piston E, and at the same time the valve piston port c has been opened, so as to exhaust from the steam chest in front of the valve piston E, and it will be readily understood that under these conditions the valve will be thrown over to its fullest extent by the direct pressure of the steam, and the main piston port G will be opened for steam, and the port G to exhaust. It will be observed that in the operation of this valve after it has been reciprocated to its extreme movement in one direction, the steam which accomplished this reciprocation remains in the steam chest at the opposite end of the valve as the valve piston ports are closed when the valve is in its extreme position. As a consequence of this when the cam I, is brought in contact with the pin H, to oscillate and move the valve to close the main piston ports, this steam acts in opposition to the movement of the valve, and especially when the engine is running under a comparatively high pressure of steam and running somewhat rapidly, the steam in the ends of the steam chest outside the pistons has little time to condense, and it exerts its fullest pressure on the valve, which has to be overcome by the cam in moving the valve. Not only this, but as the valve is moved, the pressure of the steam in being compressed, increases and offers still further obstruction to the movements of the valve which has to be overcome by the cam. It has been found that this causes considerable wear on'the cam and pin, as well as being a wastage of power, and it is with a view of preventing this wastage and wear that my present invention is made. It may be observed that this pressure is in opposition to the mechanical movement of the valve, for by the time that this movement is accomplished, the valve piston ports are opened so as to admit steam at one end of the valve against one piston and exhaust from the other. In order to accomplish this object, I provide the valve piston with what may be termed a vent hole or holes, andI have shown in the accompanying drawings the pistons E, E, as provided with one or more vent holes Z, Z, extending from their outer faces to their inner faces, their outer portions preferably being enlarged, while their smaller or contracted portions are on the insides of the pistons. It will be seen that in this construction the valve pistons are practically balanced, by the steam pressure being substantially equal on all sides, the steam passing through the vent holes with sufficient rapidity to produce this balance, so that there is practically the same pressure on each piston head, and when the valve is operated mechanically itis only necessary to exert sufiicient force on the valve to overcome the friction of the valve, resulting in less wear on the cam, and of course less force being required to move it. After the valve has been mechanically moved, in order to complete its movement by steam pressure, instead of admitting steam behind the moving valve as in the former instance, I so arrange the valve piston ports that the oscillation and partial reciprocation of the valve shall open the port or ports in the valve chest in front of the moving valve to the exhaust, which will quickly reduce the pressure of the steam in this-chamber, and allow the pressure of the steam at the op posite end of the valve to move it to open the main piston ports. It will be observed that when this exhaust port is opened, the vent or vents in the forward piston are also opened, but I make the exhaust port sufficiently large to reduce the pressure of steam, and allow the valve to move the required distance before the steam can pass through the vent holes to produce the balance, but as soon as the valve has moved its complete distance, it closes the exhaustport, and then the steam will pass through the vent holes and restore the balance ready for the next operation. Thus in. the position shown, the port e, in front of the piston E, is arranged to connect with the exhaust f, F, and this can be readily accomplished without changing the structure and arrangement of the valve proper of the Davidson engine, by simply omitting the steam ports and retaining the exhaust ports in the valve.

While I have shown my invention as applied to the ordinary Davidson pump in which the valve and pistons are made separately and secured together, it is obvious that it can be used in other forms of valves, as where the valves and pistons are made integral or are otherwise combined, and more than that, it is also obvious that this improvement may be used in connection with other means for op erating the valve as described for instance in my applications, Serial Nos. 448,508 and 448,500, filed on even date herewith, and I do not therefore limit myself to the precise construction and arrangement of parts shown in the drawings.

While I am aware that it is not broadly new to provide vent holes in valves and other similar devices, I am not aware that they have been arranged in any mannersimilar to that shown and described by me, nor for accomplishing the purposes and objects of my invention.

What I claim, therefore, is-- 1. Inapumping engine in combination with a steam chest, of a valve mounted therein adapted to be oscillated and partially reciprocated mechanically, and to be further reciprocated by steam pressure, the valve being provided with vent holes whereby it is balanced on all sides, substantially as described.

2. In a pumping engine the combination with the steam chest, of a valve and pistons mounted therein,'the pistons being provided with vent holes, the valve piston ports extending from either end of the chest to about the center thereof, and controlled by the valve, to substantially as described.

In testimony whereof I have signed my name to this specification in the presence of two subscribing witnesses.

' WM. A. DREWETT.

WVitnesses: I

JOHN LOWE, GEO. O. ESKHOLME.

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