US3877225A

US3877225A - Sawmill feedwork systems and improvements therein

Info

Publication number: US3877225A
Application number: US321480A
Authority: US
Inventors: James L Sylvester
Original assignee: Gardner Machines Inc
Current assignee: Gardner Machines Inc
Priority date: 1973-01-05
Filing date: 1973-01-05
Publication date: 1975-04-15
Anticipated expiration: 1992-04-15
Also published as: AU6342473A; CA978448A

Abstract

An improvement in sawmill feedwork systems of the shotgun type wherein safety means are provided for metering or closing fluid flow relative to the drive system such that the carriage and its load of the feedworks can be immediately stopped in the event of power or mechanical failure. In a preferred embodiment the sawyers lever includes operational means for turning off power, both electrical and mechanical. The sawyers lever is otherwise capable and is provided with structure for remotely controlling fluid flow relative to the operative piston of the feedworks.

Description

O United States Patent 1 1 1111 3,877,225 Sylvester Apr. 15, 1975 SAWMILL FEEDWORK SYSTEMS AND 2,609,665 9/1952 Rappl 60/433 IMPROVEMENTS THEREIN 2,751,752 6/1956 Metcalf 3,004,610 10/1961 Pomper et al. 60/388 X [75] Inventor: James L. Sylvester, Salt Lake C1ty,

Utah Primary ExaminerEdgar W. Geoghegan [73] Assignee: Gardner Machines, Salt Lake City,

Utah 57 ABSTRACT [22] Fled: 1973 An improvement in sawmill feedwork systems of the [21] A N 321,430 shotgun type wherein safety means are provided for metering or closing fluid flow relative to the drive system such that the carriage and its load of the feed- U.S- Cl. works can be immediately pp i the event of 91/358 91/384 power or mechanical failure. In a preferred embodi- [51] Int. Cl. FlSb 20/00 ment the Sawyers lever includes operational means for [58] Fleld of Search turning off power, both electrical and mechanical. The 60/460, 461, 466, 91/358 A, 374, 384 sawyers lever is otherwise capable and is provided with structure for remotely controlling fluid flow rela- [56] References cued tive to the operative piston of the feedworks.

UNITED STATES PATENTS 2,573,943 11 1951 Ziskal 91/384 X 12 Clams l1 Drawmg F'gures 7 g g Z5 Z4 42 2 We I9l 19 H 33 L P Q PATENTEDAPR 1 5x975 sum 2 9 3 FIG. 6

FIG. 5

SAWMILL FEEDWORK SYSTEMS AND IMPROVEMENTS TI-IEREIN V The present invention relates to what are known in the art as shotgun feedwork systems for sawmills and, more particularly, to an improved system and control therefor such that heavy masses may be both reciprocated back'and-forth in conventional rapid motions and also stopped during emergency conditions.

Sawmill feedworks are not new. Modern ones rely upon the principal of rapidly reciprocating a piston back-and-forth within a cylinder construction, and introducing hydraulic pressure at both sides, alternatively, of the piston to reciprocate the piston within the cylinder structure and also the rod connected thereto. The subject drive rod is connected to a carriage designed to reciprocate large masses.

The applicant herein is the owner of issued US. Pat. Nos. 3,049,147 and 3,651,741, which disclosures are fully incorporated herein by way of reference. The large control valve utilized to route hydraulic fluid into the cylinder system is not normally manually actuated directly but rather is controlled by a separate system incorporating what is known as a sawyers lever that is manually actuated.

In the present invention the sawyers lever includes means not only for applying and altering the direction of hydraulic fluid in the principal cylinder system of the feedworks but also for actuating gate valve means to stop fluid flow in the event of system malfunction.

Accordingly, a principal object of the present invention is to provide a new and improved sawmill feedwork system.

An additional object is to provide a safety control system for stopping the feedworks carriage in case of mechanical or power failure.

An additional object is to provide a safety control on the sawyers lever of a sawmill feedwork system such that a gate valve means can be actuated in a principal hydraulic line of the system so as to immediately stop the operating piston and rod and load connected thereto.

An additional object is to provide safety means in a sawmill feedwork such that malfunction in a feedworks, upon detection, can be prevented from causing material damage, and this by the operator being provided with control means for stopping liquid flow as de sired.

The features of the present invention may best be understood by reference to the following description taken in connection with the accompanying drawings in which:

FIG. I is a plan view, shown partially in schematic form, of a shotgun feedworks system incorporating a cylinder construction wherein the piston thereof operates to reciprocate a load bearing carrier or carriage.

FIGS. 2 and 3 are enlarged side elevations of the carrier of FIG. I when the same is approaching an extremity of travel.

FIG. 4 is a plan view of the system of FIG. 1, minus carriage, but showing the system as being modified to include gate valve means for interrupting fluid flow back to the reservoir and primary valve system associated therewith.

FIG. 5 is a view of the primary, multi-land spool valve utilized in directing fluid flow in the cylinder system of the feedworks first in one direction and then in an opposite direction; in FIG. 5 the valve is shown in neutral position wherein fluid is simply pumped but is inoperative to drive the piston of the feedworks.

FIG. 6 is a schematic view of the sawyers lever and its linkage, a pantograph system used for driving an auxiliary valve, i.e. a four-way valve used to control, via a double-acting cylinder, the primary spool valve of FIG. 5; point A of FIG. 5 is to be understood to be connected to or coupled to point A of FIG. 6.

FIG. 7 is an enlarged detail of the upper portion of a sawyers lever constructed in accordance with the present invention, wherein the lever may be tilted about a medial axis such as to actuate switch means disposed therein.

FIG. 8 illustrates the sawyers lever in a conventional operating condition and is shown in front view.

FIG. 9 is a front elevation similar to FIG. 8 but illustrates the sawyers lever as being actuated, that is, rotationally displaced about a medial axis so as to-actuate the switch means connected therein and thereby disconnect electrical power for motors, driving hydraulic pumps and also the gate solenoid controlling motion of the big gate contained in the line of the feedworks of FIG. 4; a switch means of FIG. 7 being normally opened actuation of the sawyers lever in the manner indicated in FIG. 9 actuates the switch to open the same and thereby remove power from operating motors and solenoid.

FIG. 10 is an end elevation of an air-operated valve gate structure usable in the system of FIG. 7 and also at G in FIG. 4; in FIG. 10 the valve gate is shown in open condition, with the solenoid associated therewith being energized.

FIG. 11 is similar to FIG. 10 but illustrates the gate structure thereof as being in closed position upon deenergization of the solenoid with which it is associated.

In FIG. 1 there is illustrated a composite cylinder 10 having a series of cylinders 11 bolted together at their respective flanges 11'. Disposed within the composite cylinder 10 is a piston 12 connected to a drive rod 13 in the usual manner. The latter is secured to a carrier 14 that is conventionally supplied sawmill feedworks. Side views of the carrier 14 are illustrated in FIGS. 2 and 3 wherein it is seen that the same can advance forwardly in the direction of the arrows to engage bumper or switch structure as may be provided; the latter however, forms no part of the present invention.

Returning to FIG. 1 it is seen that the composite cylinder 10 is provided with return lines 15 and 16 that lead to valve V fed by an external supply, and which is controlled by control means C, later described herein.

The control valve V is shown in FIG. 5, is conventional in construction and, with its supply system is fully disclosed in published US. Pat. No. 3,049,147, owned by the applicant herein. Thus, the valve V in FIG. 4 includes a valve spool 17 disposed within valve body 18, the same contained within an over-all reservoir system R supplying pump P of the system, see FIG. 4 and as fully disclosed in said United States issued patent.

Improved control means C in FIG. 1 is provided in this invention which shall be fully described hereinafter. Suffice it to say at this point that there is provided, in the event of line failure, a gate valve means G, and appropriate structure, wherein the gate valve when closed can block the circuit of return fluid flow so that the reciprocating equipment, namely carriage or carrier 14, is immediately stopped.

As to the control, the same includes a pantograph structure operated by what is known in the art as a sawyers lever. The latter is designated at 22. Thus, sawyers lever 22 is pivoted by suitable pivot means 23 and, beyond such fulcrum, pivotally engages by pivot means 24 lever 25. Lever 25 is in turn pivoted to the rear extremity 26 of pantograph linkage 27. The latter includes pivot means 28 as indicated. Pantograph linkage 27 preferably comprises a bifurcated link which is pivotally connected to arm 29, the latter being secured in place by pivot 30. Arm 29 in turn is centrally pivoted by pivot means 30 to a link 31. The latter in turn is pivoted to outer extremity 32 of four-way valve arm 33. Arm 33 forms a portion of fourway valve 34, the latter including housing 35. The valve includes

conventional valve gates

36 and 37 which are respectively integral with valve spool 38. The four-way valve includes a conventional inlet at 39, cylinder ports 40 and 41, and reservoir port 42. The latter is connected by suitable conduit 43 to reservoir R1 and the same is connected by conduit 44 to pump P1. Pump Pl pumps hydraulic fluid to and is connected by conduit 45 to pump or pressure port 39. It is seen that when the valve is in a central position, fluid is simply pumped into the valve and out of the same at 42 to the reservoir R1 at port 43. Should the valve be shifted one way or another, as by the pantograph system as actuated by lever 22, then hydraulic fluid is alternatively introduced via

cylindrical conduit

46 and 47 into

ports

48 and 49 of clyinder 50 containing double-acting piston 51. The piston is positiveacting in the sense that fluid coming in one side of the cylinder 50 will produce a corresponding exhaust of fluid from the remaining side. Cylinder 50 in effect forms a slave system since it follows the movement of actuating lever 22. This is to say, a pivoting of lever 22 about its fulcrum 23 produces an altering of the condition of the four-way control valve 34 so as to effect a fluid flow either into one side or into the remaining side of the double-acting cylinder 50. The same, by its linkage through piston rod 52 and the connection of the same to ball joint 53 of lever 29, will produce a corresponding movement of shaft 33 so as to return the valve to a central condition, thus terminating a pressure input into the double-acting cylinder 50. Hence, a slight movement of lever 22 in one direction will produce a displacement of the valve spool in the four-way valve illustrated in FIG. 6 such that fluid pressure is introduced into the double-acting cylinder 50. Doubleacting cylinder 50 through its piston 51 continues piston movement until the same returns through the linkage at 31 and associated

structure

32, 33 the valve spool 38 to its original condition. It is noted that piston rod 52 is connected by linkage 54 to the valve spool 17 in FIG. 5. it has been fully shown in the aforementioned United States Patent which is incorporated herein fully by way of reference. that valve spool displacement in one direction produces an outward thrusting of rod 13 in FIG. I so as to translate the carriage to the left; correspondingly, a reversal of the valve displacement in FIG. 5 causes a retrieval of the rod 13. Accordingly, lever 22 comprises means for rapidly reciprocating the carriage or carrier 14 relative to the cylinder system at 10.

In the event of line leakage it might well be impossible to control the rapidly moving reciprocating mass associated with carrier 14. Accordingly, lever 22, comprising the sawyers lever, may in fact itself include a pivot control such that the lever is modified as shown at 22A in FIG. 7. It will be understood that the lever still includes the fulcrum pivot at 23 and connection at 24 as seen in FIG. 6. Thus, the upper portion of lever 22A comprises a hand grip 55. The same is pinned by pin 56 to casing 57 and includes a ball portion 58 held in place by nut 59. The end 60 is preferably flat and includes a corner or peripheral edge 61. The same engages the upper surface 62 of plunger 63. Plunger 63 is spring-biased against surface 62 by compression spring 64. The lower end of the latter also coacts against a cylindrical retainer 65. Lower portion 66 is threaded and receives casing 57. Centrally disposed is a microswitch 67 that has an actuatable button 68. The microswitch is normally closed and is inserte'd in series in the electrical circuit including leads 69, 70, 71 and 72 and also motors M and m, driving pumps P and P1. Likewise inserted is the valve gate solenoid GS, otherwise identified as 73 in FIG. 7. The same operates a gate valve 74, termed G in FIGS. 4 and 7. Gate valve solenoid 73 may directly actuate a gate valve so as to close the same or simply open an air supply to thrust the gate closed. Both types of gate valves are conventional and are well known in the art. Thus. these include either the direct solenoid actuated valves or the air actuated valves in which air is supplied via solenoid actuated release. This is strictly conventional. What is important is that the sawyers lever 22A as above described may be fulcrumed or pivoted about the central ball joint .1 so as to actuate microswitch 67. It is seen that the latter is normally closed, that is when the button of the microswitch is disposed upwardly. When the same is depressed as through the bending of the handle portion 55, then the normally closed switch becomes opened so as to break the circuit to motors M and m. It will be seen that motors M and m control respective pumps P and P1. The former, pump P, will supply pressure fluid to valve V in FIG. 5 whereas the small pump P1 supplies pressure and hydraulic fluid to the four-way valve 34 in FIG. 6. Additionally. it is seen that the breaking of the circuit as by the actuation of the microswitch to its closed position, in turn breaks the circuit of the gate circuit which is so designed that, upon deenergization, the valve gate at 74 closes. This is the same valve gate as illustrated at G in FIG. 4. FIG. 10 illustrates a valve gate 74 open" condition whereas the gate G in FIG. 11 of the valve gate structure is in closed position upon de-energization of solenoid 73. In the case of the embodimennt shown in FIGS. 10 and 11 the valve gates are air operated, with the solenoid controlling the flow of air from air pressure source PA through the cylinder CY actuating gate G. The particular type of gate valve employed is optional, save only that the same be responsive to change in electrical condition as aforesaid and fully described.

What is provided is an improved shotgun feedworks type of system for reciprocating heavy masses such as logs in the lumber industry. The sawyers lever is modifled so that in addition to controlling the speed and direction of motion of the drive rod and its carrier, the sawyers lever also can be pivoted about a transverse axis such as to electrically actuate safety valve means. Thus, to introduce by rapid motion a gate valve in a return cylinder path such as to immediately stop the travel of the reciprocating apparatus.

It is thus seen that the subject safety control system is an independent system for stopping the carriage in case of mechanical or power failure. The actuator provided in the sawyers lever which operates to trip the safety gate valve under any circumstances. this by the operator exerting more pressure on the handle than when it is encountered or used under normal operating conditions.

By gate valve" is meant any valve, though preferably of the gate-drop type, constructed for rapidly closing or metering one conduit branch, as at or 16 in FIG. 1, of the subject primary hydraulic circuit.

While particular embodiments of the invention have been shown and described. it will be obvious to those skilled in the art that various changes and modifications may be made without departing from the essential features of the present invention and, therefore, the aim in the appended claims is to cover all such changes and modifications as fall within the true spirit and scope of the invention.

I claim:

1. In a sawmill feedworks having a cylinder, a reciprocable piston disposed within said cylinder, a piston rod secured to said piston and extending outwardly from said cylinder, a carrier fixed to said piston rod and constructed to reciprocate and carry an external load in accordance with the movement of said piston, plural conduit connected to opposite ends of said cylinder, a reservoir and pump combination for supplying pressurized fluid to and exhausting fluid from said plural conduit, electrical circuit means for supplying electrical power to drive said pump. primary valving means operatively interposed between said plural conduit and said reservoir and pump combination for selectively introducing pressurized fluid therein and exhausting fluid therefrom to reciprocate said piston, and control means for operatively controlling the operative condition of said primary valving means: an improvement comprising gate valve means interposed in one of said plural conduit, said control means including safety means responsive to electrical power failure for automatically closing said gate valve means and wherein said control means comprises a sawyers lever, and linkage means intercoupling said sawyers lever with said primary valving means, said sawyers lever including said safety means.

2. In a sawmill feedworks having a cylinder, a reciprocable piston disposed within said cylinder, a piston rod secured to said piston and extending outwardly from said cylinder, a carrier fixed to said piston rod and constructed to reciprocate and carry an external load in accordance with the movement of said piston, plural conduit connected to opposite ends of said cylinder, a reservoir and pump combination for supplying pressurized fluid to and exhausting fluid from said plural conduit, electrical circuit means for supplying electrical power to drive said pump, primary valving means operatively interposed between said plural conduit and said reservoir and pump combination for selectively introducing pressurized fluid therein and exhausting fluid therefrom to reciprocate said piston, and control means for operatively controlling the operative condition of said primary valving means: an improvement comprising gate valve means interposed in one of said plural conduit, said control means including safety means responsive to electrical power failure for automatically closing said gate valve means and wherein said electrical circuit means includes electrical means for opening, when energized, said gate valve means,

said safety means comprising switch means electrically interposed in said electrical circuit for interrupting said circuit to close said gate valve means and shut off said pump,

3. The apparatus of claim 2 wherein said sawyers lever includes reaction means, said safety means including electrical switch means selectively actuated by said reaction means.

4. The apparatus of claim 2 wherein said sawyers lever includes an upper member and a hollow lower member, said upper member having a lower portion disposed within said lower member, said lower portion having a bottom reaction surface, a spring-biased plunger positioned within said lower member and engaging said upper member at the latters reaction surface, said switch means being a normally-closed switch and being positioned within said lower member for selective actuation by said plunger when said upper member is pivoted relative to said lower member.

5. Apparatus according to claim 2 wherein said control means includes a lever, a four-way valve, a secondary pump for supplying pressurized fluid to said fourway valve, a double-acting cylinder operatively connected to said four-way valve, said double-acting cylinder including a double-acting piston provided with a piston rod, said piston rod being operatively linked to said primary valving means, and a pantograph system interlinking said four-way valve, double-acting piston and said lever, whereby to return said four-way valve upon movement of said double-acting piston in correspondence with the selected positionment of said lever.

6. The apparatus of claim 5 wherein said secondary pump is included in and powered by said electrical circuit means when the latter is closed.

7. A sawmill feedworks including, in combination, a cylinder, a reciprocable piston disposed within said cylinder, a piston rod secured to said piston and extending outwardly from said cylinder, a carrier fixed to said piston rod and constructed to reciprocate and carry an external load in accordance with the movement of said piston, plural conduit connected to opposite ends of said cylinder, a reservoir and pump combination for supplying pressurized fluid to and exhausting fluid from said plural conduit, electrical circuit means for supplying electrical power to drive said pump, primary valving means operatively interposed between said plural conduit and said reservoir and pump combination for selectively introducing pressurized fluid therein and exhausting fluid therefrom to reciprocate said piston, control means for operatively controlling the operative condition of said primary valving means, and gate valve means interposed in one of said plural conduit, said control means including safety means responsive to electrical power failure for automatically reducing fluid flow through said gate valve means, and wherein said control means comprises a sawyers lever, and linkage means intercoupling said sawyers lever with said primary valving means, said sawyers lever including said safety means.

8. A sawmill feedworks including, in combination, a cylinder. a reciprocable piston disposed within said cylinder, a piston rod secured to said piston and extending outwardly from said cylinder, a carrier fixed to said piston rod and constructed to reciprocate and carry an external load in accordance with the movement of said piston. plural conduit connected to opposite ends of said cylinder, a reservoir and pump combination for supplying pressurized fluid to and exhausting fluid from said plural conduit, electrical circuit means for supplying electrical power to drive said pump, primary valving means operatively interposed between said plural conduit and said reservoir and pump combination for selectively introducing pressurized fluid therein and exhausting fluid therefrom to reciprocate said piston, control means for operatively controlling the operative condition of said primary valving means, and gate valve means interposed in one of said plural conduit, said control means including safety means responsive to electrical power failure for automatically reducing fluid flow through said gate valve means, and wherein said electrical circuit means includes electrical means for opening, when energized, said gate valve means, said safety means comprising switch means electrically interposed in said electrical circuit for interrupting said circuit means to close said gate valve means and shut off said pump.

9. The apparatus of claim 8 wherein said sawyers lever includes reaction means, said safety means. said safety means including electrical switch means selectively actuated by said reaction means.

10. The apparatus of claim 8 wherein said sawyers lever includes an upper member and a hollow lower member, said upper member having a lower portion disposed within said lower member, said lower portion having a bottom reaction surface, a spring-biased plunger positioned within said lower member and engaging said upper member at the latters reaction surface, said switch means being a normally closed switch and being positioned within said lower member for selective actuation by said plunger when said upper member is pivoted relative to said lower member.

1 1. Apparatus according to claim 8 wherein said control means includes a lever, a four-way valve, a secondary pump for supplying pressurized fluid to said fourway valve, a double-acting cylinder operatively connected to said four-way valve, said double-acting cylinder including a double-acting piston provided with a piston rod, said piston rod being operatively linked to said primary valving means, and a pantograph system interlinking said four-way valve, double-acting piston and said lever, whereby to return said four-way valve upon movement of said double-acting piston in correspondence with the selected positionment of said lever.

12. The apparatus of claim 11 wherein said secondary pump is included in and powered by said electrical circuit means when the latter is closed.

Claims

1. In a sawmill feedworks having a cylinder, a reciprocable piston disposed within said cylinder, a piston rod secured to said piston and extending outwardly from said cylinder, a carrier fixed to said piston rod and constructed to reciprocate and carry an external load in accordance with the movement of said piston, plural conduit connected to opposite ends of said cylinder, a reservoir and pump combination for supplying pressurized fluid to and exhausting fluid from said plural conduit, electrical circuit means for supplying electrical power to drive said pump, primary valving means operatively interposed between said plural conduit and said reservoir and pump combination for selectively introducing pressurized fluid therein and exhausting fluid therefrom to reciprocate said piston, and control means for operatively controlling the operative condition of said primary valving means: an improvement comprising gate valve means interposed in one of said plural conduit, said control means including safety means responsive to electrical power failure for automatically closing said gate valve means and wherein said control means comprises a sawyers lever, and linkage means intercoupling said sawyers lever with said primary valving means, said sawyers lever including said safety means.

2. In a sawmill feedworks having a cylinder, a reciprocable piston disposed within said cylinder, a piston rod secured to said piston and extending outwardly from said cylinder, a carrier fixed to said piston rod and constructed to reciprocate and carry an external load in accordance with the movement of said piston, plural conduit connected to opposite ends of said cylinder, a reservoir and pump combination for supplying pressurized fluid to and exhausting fluid from said plural conduit, electrical circuit means for supplying electrical power to drive said pump, primary valving means operatively interposed between said plural conduit and said reservoir and pump combination for selectively introducing pressurized fluid therein and exhausting fluid therefrom to reciprocate said piston, and control means for operatively controlling the operative condition of said primary valving means: an improvement comprising gate valve means interposed in one of said plural conduit, said control means including safety means responsive to electrical power failure for automatically closing said gate valve means and wherein said electrical circuit means includes electrical means for opening, when energized, said gate valve means, said safety means comprising switch means electrically interposed in said electrical circuit for interrupting said circuit to close said gate valve means and shut off said pump.

4. The apparatus of claim 2 wherein said sawyers lever includes an upper member and a hollow lower member, said upper member having a lower portion disposed within said lower member, said lower portion having a bottom reaction surface, a spring-biased plunger positioned within said lower member and engaging said upper member at the latter''s reaction surface, said switch means being a normally-closed switch and being positioned within said lower member for selective actuation by said plunger when said upper member is pivoted relative to said lower member.

5. Apparatus according to claim 2 wherein said control means includes a lever, a four-way valve, a secondary pump for supplying pressurized fluid to said four-way valve, a double-acting cylinder operatively connected to said four-way valve, said double-acting cylinder including a double-acting piston provided with a piston rod, said piston rod being operatively linked to said primary valving means, and a pantograph system interlinking said four-way valve, double-acting piston and said lever, whereby to return saiD four-way valve upon movement of said double-acting piston in correspondence with the selected positionment of said lever.

8. A sawmill feedworks including, in combination, a cylinder, a reciprocable piston disposed within said cylinder, a piston rod secured to said piston and extending outwardly from said cylinder, a carrier fixed to said piston rod and constructed to reciprocate and carry an external load in accordance with the movement of said piston, plural conduit connected to opposite ends of said cylinder, a reservoir and pump combination for supplying pressurized fluid to and exhausting fluid from said plural conduit, electrical circuit means for supplying electrical power to drive said pump, primary valving means operatively interposed between said plural conduit and said reservoir and pump combination for selectively introducing pressurized fluid therein and exhausting fluid therefrom to reciprocate said piston, control means for operatively controlling the operative condition of said primary valving means, and gate valve means interposed in one of said plural conduit, said control means including safety means responsive to electrical power failure for automatically reducing fluid flow through said gate valve means, and wherein said electrical circuit means includes electrical means for opening, when energized, said gate valve means, said safety means comprising switch means electrically interposed in said electrical circuit for interrupting said circuit means to close said gate valve means and shut off said pump.

9. The apparatus of claim 8 wherein said sawyers lever includes reaction means, said safety means, said safety means including electrical switch means selectively actuated by said reaction means.

10. The apparatus of claim 8 wherein said sawyers lever includes an upper member and a hollow lower member, said upper member having a lower portion disposed within said lower member, said lower portion having a bottom reaction surface, a spring-biased plunger positioned within said lower member and engaging said upper member at the latter''s reaction surface, said switch means being a normally closed switch and being positioned within said lower member for selective actuation by said plunger when said upper member is pivoted relative to said lower member.

11. Apparatus according to claim 8 wherein said control means includes a lever, a four-way valve, a secondary pump for supplying pressurized fluid to said four-way valve, a double-acting cylinder operatively connected to said four-way valve, said double-actIng cylinder including a double-acting piston provided with a piston rod, said piston rod being operatively linked to said primary valving means, and a pantograph system interlinking said four-way valve, double-acting piston and said lever, whereby to return said four-way valve upon movement of said double-acting piston in correspondence with the selected positionment of said lever.