US2779141A

US2779141A - Railgrinder

Info

Publication number: US2779141A
Authority: US
Inventors: Jr Frank Speno; Shay George Clinton
Original assignee: Speno International SA
Current assignee: Speno International SA; Frank Speno Railroad Ballast Cleaning Co Inc
Priority date: 1955-11-15
Filing date: 1955-11-15
Publication date: 1957-01-29
Anticipated expiration: 1974-01-29

Description

Jan. 29, 1957 F. SPENO, JR, ET AL 2,779,141

RAILGRINDER 4 Sheets-Sheet J.

INVENTOR Filed Nov. 15, 1955 ATTORNEY5 Jan. 29, 1957 F. SPENO, JR, ET AL 2,779,141

RAILGRINDER Filed Nov. 15, 1955 4 Sheets-Sheet 2 INVENTOR /7 I V na/72A {aww g BY Z Qb C. flzfiwb, 6%, s n/MM 7W5 ATTORNEYS Jan. 29, 1957 F. SPENO, JR, ETAL 2,779,141

RAILGRINDER Filed Nov. 15, 1955 4 Sheefs-Sheet :s

INVENTOR J/zam/w ,J wna- BY fire C [Any i/wzzm, M, wax u/Lzm ATTORNEY5 Jan. 29, 1957 F. SPENO, JR, ETAL 2,779,141

RAILGRINDER Filed Nov. 15, 1955 7 4 Sheets-Sheet 4 INVENTOR ATTORNEYS United States Patent RAILGRKNDER' Frank Speno, Jr.,. Summit, and George Clinton Shay, New Providence, N. J., assignors to Frank Speno Railroad Ballast Cleaning Co. Incorporatedylthaca, N. Y., a corporation of New York Application November 15,1955, Serial. No. 546,885

19 Claims. (Cl".5 1'--1'78) This invention relates. to a rail'grinder and more particularly to improvements in a railgrind'er of. the type ex- 7 emplified in the disclosure of" United States Patent No. 2,197,729 to Miller.

In railgrinders of this type it is usual to suspend the grinding heads in gangs from carriages or trucks adapted to move the grinding heads along the rails. The several grinding heads of each gang, each grinder head including its associated electric driving motor, are normally disposed for generally vertical movement into and out of grinding engagement with the rails; under the actuation of hydraulic means; A pneumatic" pressure system supplies actuating pressure from suitable sources to the several hydraulic means, either at a relatively'redueed pressuresuficient tocounterbalance but a portion of the weight of each grinder head on the rails; and thereby to regulate the grinding pressure,.or alternatively supplies full pressure sufficient to simultaneously raise the several grinder heads fromthe rails, for clearing crossings or obstructions, or when the carriage are" brought to a stop; In prior rail grinders of such' type it' has been com.- mon practice to supply'the same reduced counterba1anc= ingpneumatic pressure to each of thehydraulic' means of a given gang or group, through a pressure regulator common to all of said gang, and to provide a' manually controllable valve operable to permit the supplying of additional pressure around the pressure regulator to the several hydraulic means for lifting; the grinderheads of a gang simultaneously from the rails.

However, such prior arrangement, with its-equalcoun terbalancing of .a plurality of grinder'heads, has in" practice resulted in unequal loading of the several grinder motors, with resultant loss of efiiciency and sacrifice of grinding speed, it being apparent in such casethat the sev eral grinder head motors can operate only at a reduced power level in order to'avoid overloading of'those' doing the most work. This results: from such factors as' variations in weight resulting from wear' on the respective grinding wheels, variationsin inclination between the several grinder heads, variations in co-eflicient of friction". of different grinding wheel's; variations'inmaterial, hardhess, etc. of different wheels. The cumulative" effect of" these several variations may cause a very substantial variation in the loads imposedon the several motorsj of a gang of grinder heads.

It is, therefore, a primary object of theinveution to provide a railgrinder embodying means for individually adjusting and equally loading the several grinder head motors of each gang to permit operation at' maximum motor efficiency of each grinder head, to therebyreal-ize a maximum rate of metal removed from" the rails. An advantage inherent in this arrangement is that, by-virtue of such adjustment of the several grinder heads, these will remove metal at the same rate from the rails, thereby permitting the grinding of a more con'sistentlyuniform profile on the rail than has heretofore been possible.

Preferably individual ammetersare provided" in; cir suit withthe respective grinder motors'to facilitate the 2. loading. of these motors to the desired extent by the adjustment. above mentioned.

In. accordance-with the invention, both the reduced or relatively low pneumatic pressure for activating the hydraulic system to counterbalance the several grinder heads off each gang, and the relatively high or full pressure for causing the hydraulic means to raise thegrinder heads, are transmitted to the several hydraulic systems through novelly arrangeddifferentialpressure valves automatically controllable responsive to admission of or release of pressure from the high pressure side of the respective valves.

Also, in accordance with the invention, the admission or release'of the controlling high pressure to or from the several differential pressure valves of each gang will normally be. through a control. valve common to all such differential valves.

A further highly important object of the invention consists in the novel arrangement of these several differential valves whereby, after its associated hydraulic systemhas'been' activated by high pneumatic pressure to raise the grinder head; each such valve will automatically function, responsive to release of the high pressure, to release said high pressure from its controlling relation with" the hydraulic system, beforeplacing such system under the control of'i-ts relati'velylower and individually adjusted counterbalancing pressure.

A still further object consists'in providing a speed responsive master control valveconnectedin series with the several control valves of the respective gangs of grinder heads; for automatically introducing air at high pressure through said valves, or exhausting air therefrom, responsive to changes in the speed of the grinder head along the rails. The purpose of the speed responsive master control valve is to automatically raise the grinder heads from the rails as the carriages or trucks carrying the several gangs of grinder heads approach a stop; This prevents thegrind'er heads from damaging the rails by grin-ding'a series ofdeep slotsor cuts therein.

In. the: accompanying drawings:

Figure. 1 is aside elevation of a railroad car showing generally th'ezmanner in which the preferred embodiment of the invention is applied thereto;-

Figure 2 is adiagramma'tic'side elevation of one of the grinder heads andrits associated supporting means;

Figure 3 isa vertical cross-section through the control console of. the invention;

Figure 4 is1 a view of said console from the rear, or as seen: from the: right in: Figure 3';

Figure 5 is a diagrammatic view of the entire control system: of the invention.

Referring now in detail to'tlie accompanying drawings, the numeral 1. designates in" its entirety a railway can incorporating the-I improved: rail: grinding apparatus of the invention. The grinding. apparatus includes a pair of duplicate trucks 2 and 2a which are suspended one behind theother beneath car 1 in therinterval' between the car wheels 3'3.

. Each of these trucks- 2 and 2a is provided with usual flanged wheels 4 adapted: to support it for movement along the rai1s:R in usual manner,.the'said trucks being adapted for movement alon'g-the rails with earl.

Each such truck carries a: gang of grinder heads 5, preferably arranged. three on:- each side, for operative grinding'engagementwith the respective rails.

Sincethetrucksfi, their suspensiontfrom the car 1 and connectionsthereto, aswellas the: grinder heads 5 per. se, constitute nopartvofamy inventiombut have heretofore been patentedand described in: detail in the aforesaid Miller patent,.these. elements are-but generally illustrated in the: accompanying. drawings.

Each. such grinding. head. 5' comprisesv agrinding disc 6 fixed'to the depending driven shaft 7 of an electric motor 8 for grinding engagement with a rail R, as is best shown in Figure 2. The motor 8 and grinding disc 6 are vertically supported in a cradle fixed to the truck 2 or 2a. Each such cradle comprises relatively spaced upper and lower members 9 and 10 rigidly interconnected by vertical rods 11. The motor support 12 projects laterally outwardly and has boxes therethrough which slidably receive bars or rods 11 to guide the grinding head in its vertical movement. Fixed on opposite sides of the lower cradle member 10 are vertically disposed hydraulic cylinders 13. Reciprocally disposed in these cylinders are pistons 14 respectively having their piston rods 15 connected to the motor support 12 and governing the vertical position of the grinder head. Actuating liquid is admitted to and withdrawn from the cylinder 13 through a pipe 16 interconnecting the cylinders of each pair, and a flexible conduit 17 connecting pipe 16 to an enclosed reservoir 18 mounted on the car 1.

Each such reservoir 18 contains a supply of oil or other hydraulic fluid F which is supplied to its associated pair of cylinders 13 at a pressure equal to that of the air supplied to the upper part of the reservoir through a conduit 20 communicating with the reservoir 18 above the normal level of the fluid F therein.

The weight of the grinder head 5 normally opposes the pressure of the fluid within the supporting hydraulic cylinders 13, and thus tends to return the oil to the reser voir 18 in the event of a pressure drop Within the reser voir suflicient to permit lowering of the grinder head. Accordingly, the cylinder 13 need be of the single acting type only, adapted to exert a lifting force on the associated grinder head.

Normally air will be supplied through the conduit 20 to reservoir 18 at a regulated constant pressure suflicient only to partially counterbalance the weight of the grinder head 8, and to control the grinding pressure of its disc 6 on the rail.

In order to permit individual adjustment of the grinding pressures of the several grinder heads, to the end that their electric motors 8 may be properly loaded for eflicient operation, as well as to attain the other advantages herein enumerated, it is an important feature of the invention to provide separate reservoirs 18, each with its own individually regulatable fluid pressure supply source.

Each such individually regulatable fluid supply source is exemplified by a conventional air pressure regulator or reducer 21 of the bleed-off type, having a manually controllable adjusting hand wheel 22. It is desirable to mount all of these regulators 21 on a common control console 23 enclosed in a cab 24 on the railway car 1, as illustrated in Figures 1 and 3. Each of the regulators 21 is supplied with air at relatively high pressure through a line 25 from a regulator manifold 26 housed in con sole 23. The manifold 26, which is in communication with all of the regulators 21 of its associated gang of grinder heads, may be supplied with air at relatively high pressure from any suitable source, exemplified by the delivery pipe 27.

The air, after passing through each pressure regulator 21, is delivered therefrom at the desired relatively reduced pressure, into a conduit 28 which normally communicates, through a differential pressure shuttle valve 29 with the conduit leading to its associated reservoir 18.

It is desirable also to arrange a series of ammeters 30 on the control console 23, individually in circuit with respective grinder motors 8. This makes it possible for an operator in the cab 24 to keep continuously informed relative to the loading of the respective motors 8, as determined by adjustment of their individual pressure regulators as well as by other external conditions.

Also it is desirable to provide on the console 24 a series of air pressure gauges 31, each operatively connected through a tube 32, with the conduit 28 on the output side of its respective regulator. By observing the vet-sing valves of the four-Way type.

readings of the said air pressure gauges 31 in conjunction with the ammeters 30 the operator is able to detect unusual conditions, such as excessive wear indicating the need for replacement of any of the grinding discs 6.

While the differential pressure shuttle valves 29 are not essential to the counterbalancing mechanism thus far described, they are important adjuncts to a further novel feature of the invention. In accordance with such feature air, supplied to the valves 29, under the control of a control valve 33 (Fig. 5) common to all of the differential valves of a given gang of grinder heads, may act through said differential valves to simultaneously raise said grinder heads out of operative engagement with the rails, when it is desired to clear an obstruction such as a crossing.

As indicated diagrammatically in Figure 5, each such differential valve comprises a cylindrical valve casing 34 having the low pressure air line 28 from its regulator 21 communicating therewith through one axial end.- At its opposite axial end casing 34 communicates with a line 35 leading to a shuttle valve manifold 36, which communicates through the several lines or branches 35 with each of the respective valve casings 34.

The conduit or line 19 to the associated oil reservoir 18 of each shuttle valve 29 communicates with such valve medially of its length through the cylindrical wall of its valve body 34. Each valve 29 per se is of conventional construction, including therein a valve body or shuttle 37 which is freely axially movable, responsive to pressure differential on opposite sides thereof, between operative position on opposite sides of the point of entry of line 20. Thus, in operation the valve shuttle 37 will function to establish communication between line or conduit 20 and whichever of the

lines

29 or 35 supplies air at the higher pressure.

Normally, the line 35 of each valve 29 will be in communication with the atmosphere, as hereinafter described in detail, while air at a relatively low pressure greater than atmospheric pressure will enter the valve from the low pressure air supply source exemplified by the regulating valve 21 and its connecting line 28 to the diiferential valve. Thus the shuttle 37 will automatically be positioned at the right hand end of the valve casing 34, as shown in Figure 5, to establish communication between the regulator 21 and its associated oil reservoir 18.

The aforementioned control valve 33 for each gang of grinder heads, is in communication through a pipe 38 with the shuttle valve manifold 36, the several branches 35 of which communicate with the respective shuttle valves 29. Normally, the control valve 33 establishes communication between the shuttle valve manifold 36 and an exhaust manifold 39 which communicates with the valve 33 through a line 40. Manifold 39 in turn communicates with the atmosphere through a discharge pipe 41, whereby the low pressure air supplied through the regulator 21 acts on the several hydraulic systems to regulate the grinding pressure of the several grinder heads 5.

The air supply for each of the several regulators 21 of each gauge of grinders also is norm-ally delivered through the control valve 33 by the conduit 42 establishing communication between the control valve and the air supply manifold 43, thence through the line 27 to the regulator manifold 26.

It is the function of the control valve to transpose these connections when desired, to thus selectively interconnect the conduits 39 and42 with the

conduits

27 and 38 respectively. To this end, control valve 33 may comprise any of various conventional manually operable re- It will be apparent that when the valve 33 is thus reversed, the air supply manifold 43 will communicate through the line 42, control valve 33, line 38 and shuttle valve manifold 36, with the several differential valves 29 to supply air to these valves at a relatively higher pressure than that supplied througuh the several regulators. Thus, the air supply manifold 43, when connected through controb valve 33 and shuttle valve manifold 36 to theditferentialpressure responsive shuttle valves 29 may be regarded as-a source of air at relatively high pressure, as compared to the low pressure source constituted-by-the regulators 21, in conjunction with air supply manifold 43.

It will be apparent that each ofthe gangs of grinder heads 5 carried by the respectivetrucks 2, 2a: may employa common air supply manifold-43 and a common exhaust manifold 39. However, each will employ its own individual shuttle valve manifold 38' and regulator manifold 26 respectively. This is necessaryin order that the control valves 33 may independently control their respective fluid pressure responsive means. Thus it will be seen in Figure l'that the shuttle valve manifolds 38-38 are separated by a partition 44 andrthe regulator manifolds 2626 are similarly-separated by a partition 45;

In the normal operation of the mechanism thus far described, the control valve 33foreach gang of grinder heads 5 is set to maintain communication between'itsair supply manifold 43 and regulator manifold 26, and between its shuttle valve manifold'andthe exhaust manifold 39.

Thus air at relatively reducedpressures-entering the shuttle valves 34 from their'respective regulators 21'will normally urge the shuttle 37 of each' valve acrossthe inlet end of its conduit 20, thereby preventing escape: of the air through pipe 38 and permitting communication between conduits 2i) and 21, whereby such air will'exert pressure on the surface of. the oil or other fiuidin-the respective reservoirs 18;. This will. cause: the; several pressure responsive means, including the reservoirs 18 and their associated hydraulic: cylinders: 13. to-counterbalance the weights of the: respective.grinder'headsS, and thereby to support each of thesegrinder; heads. in operative engagement with the; railatagrindingzpressure which will obviously depend on the individualzadjustment: of its associated pressure regulator 21. Byseparate: adjustments of the regulators 21 theseveral grinder heads of each gange may be caused to engagetherail'at grinding pressures which will load the respectivemotors 8* to the desired extent. Such loading of. each motor 8 may be readily and continuously ascertained; in thepreferred embodiment by reference to theammeter 30in circuit'therewith. Obviously, the grinding. pressures of the several grinder heads 5 will requireadjustment from time totime during the course of the rail grinding operation to compensatefor the inevitable wearing away of their grinding discs or elements 6. The, necessity for each-adjustment may be ascertained by reference to the several ammeters. Also by referring to; the air pressure gauges 31 associated with the pressure regulators, 21, and'considering the readings of these in conjunction with the readings of the ammeters, a skilled operatorwill be able to detect various conditions requiring correction andmay make timely adjustmentor replacement of elements accordingly.

When it is wished to raise a gauge of grinder. heads 5, as for instance when it is desired to'cleara. crossing or obstruction, the control valve 33 for that particular gang or group is manually actuated to establish communication between the airsupply manifold 43 and the shuttle valve manifold 38, and between the regulator manifold 26 and the exhaust manifold 39. This will result in supplying air at'relatively. high pressure through the pipes 38 and manifold 3.6. to shuttle valves 29, causing the shuttles 37 thereof to move across the-medial ports defined by the inlet end of pipes 20- and toward the low pressure ports defined by the inlet ends of conduits 28, to thereby permit entry of such high pressure air'to the reservoirs 18, while preventing. escape of such high pressure air through the relatively high pressure ports defined by the inlet ends of the respective conduits 35 The relatively low'pressure air trapped in the valves between shuttles. 37 andconduits 28 may escape through said conduits: and bebled 0H 01'' exhausted through the regulators.

When control valve 33 is again positioned or actuated to lower the grinder heads by re-establishing communication between the air supply manifold 43 and regulator manifold 26, and between the shuttle valve manifold 36 and exhaust manifold 39, the shuttle 37 of'each differential pressure actuated shuttle valve- 29 will delay in rte-establishing communication between the conduits 28 and 35 (and the axially opposed'low pressure and high pressure ports defined thereby) until after the air pressure within-the oil reservoir 18 and between the shuttle 37" and conduit 35 of each valve has been reduced'below the supply pressure of the regulator 21 by exhaustion through conduit 35. Communication between the conduits- 35and the atmosphere will, of course, permit exhaustion of air which might otherwise be trapped between the shuttles 37 and theports defined byconduits 35'at their inlet ends and which might otherwise obstruct the movement of the shuttle.

Speedv responsive master control valve The several control valves 33, above mentioned, are arranged so that each such valve must be separately manually actuated to raise the particular gang of grinder heads which it controls. In order to prevent the grinder heads S'from grinding a series of' slots in the rails, as would obviously occur. if the train were brought substantially to a stop-without raisingthe grinder heads from the rails, there'isprovided a speed responsive master control valve 46, (Fig. 5) operable to simultaneously raise all of the grinder heads from the rails. when the train speed drops below-a predetermined minimum.

To this end, the air supply manifold 43 and exhaust line 41 areinterconnected by a bypass line 47in which is: interposed the master control valve 46, preferably of. a reciprocating solenoid actuated type, capable of establishing communication between the exhaust manifold 39 and-through its exhaust line 41 either with the atmosphere or the airsupply manifold 43. Normally the exhaust manifold 35 communicates with the atmosphere through exhaust line 41 and the mechanism is controlled'by manual actuation of the control valves 33 in the manner above-mentioned. However, when master valve; 46 is positioned to place the exhaust manifold 39 in communication with the airsupply manifold 43, responsive to decrease of the train speed beyond the predetermined minimumof say one mile per hour, it will be seen that the full air pressure will be supplied through

lines

39 and 38 and the several control valves 33 to the shuttle valve manifold 36 and ultimately to the reservoirs 18, to accomplish the desired result of raising the several grinder heads from the rails.

The master control valve 46 has its solenoid 43 energized at appropriate times by current supplied through wiresSl and 52 from any suitable-source through a usual speed responsive governor controlled switch 49- (Fig; 1)., the. governor mechanism of which is driven through a chain drive 50 from the adjacent axle of the truck 2on which switch 49 is supported. The arrangement is pref erably such that the switch 49 will remain open at normal operating speeds so that the solenoid'48 will remain deenergizedand thereby position the valve 46 to maintain the: line 41 from the exhaust manifold in communication with the atmosphere, and will be closed to energize the solenoid and thereby actuate the valve 46 to raise the several grinder heads 5 in the manner above-mentioned, when the train drops below its predetermined minimum speed.

Having thus described our invention, we claim:

1. A rail grinder comprising a truck movable along :a rail, a plurality of grinder heads supported by said truck for operative engagement with the rail, a similar plurality of hydraulically actuated means separately associated with the respective grinder heads for vertically supporting and adjusting each such grinder head, an enclosed oil reservoir communicating with each such hydraulically actuated means, a series of shuttle valves, each having a medial port communicating with one of said oil reservoirs, a shuttle freely movable in each said valve between operative positions on opposite sides of said medial port, responsive to differing air pressures on opposite sides of said shuttle, an air supply manifold communicating with the respective valves on corresponding sides of their said shuttles, an adjustable pressure regulator interposed between the supply manifold and each said valve to regulate the pressure of the air delivered to the respective valves, a control valve communicating with each of the several shuttle valves on opposite sides of their respective shuttles from said manifold, said control valve also normally communicating with said high pressure air source and with the atmosphere and being operable to place said shuttle valves in communication with either the said source of high pressure or with the atmosphere.

2. The combination of claim 1 wherein each of the grinder heads includes its own electric driving motor, and an ammeter in circuit with each such motor for indicating when the said grinder head is loaded to its rated capacity as determined by the adjustment of said pressure regulating means.

3. A rail grinder comprising a truck movable along a rail a plurality of grinder heads supported by said truck for operative engagement with the rail, a similar plurality of hydraulically actuated means separately associated with the respective grinder heads for vertically adjusting and partially counter-balancing said heads, an enclosed oil reservoir communicating with each such hydraulically actuated means, a series of shuttle valves, each having a medial port communicating with one of said oil reservoirs, a valve body freely movable in each said valve between operative positions on opposite sides of said medial port, responsive to differing pressures on opposite sides of said body, individually regulable relatively low pressure fluid sources each communicating with one end of one said shuttle valve on one side of its said body, a source of fluid under relatively high pressure, and a common means interconnected between said high pressure fluid source and each of said shuttle valves through the opposite end thereof, for selectively placing all of said valves in communication either with said high pressure source or with an exhaust passage.

4. A rail grinder comprising a truck movable along a rail, a plurality of grinder heads guided on said truck for generally vertical movement into and out of engagement with the rail, a similar plurality of pressure responsive means separately associated with the respective grinder heads for vertically adjusting and partially counterbalancing each of said heads, a series of shuttle valves, each having a medial port communicating with one of said pressure responsive means for admitting an actuating pressure thereto, a valve body freely movable in each said valve between operative positions on opposite sides of said medial port, responsive to differing pressures on opposite sides of said body, relatively low pressure fluid sources each communicating with one said diiierential valve on one side of its said body, and means communicating with each said valve on the other side of its said body for simultaneously and selectively admitting a fluid under high pressure to or exhausting it from the respective valves.

5. A rail grinder comprising a truck movable along a rail, a plurality of grinder heads guided on said truck for generally vertical movement into and out of engagement with the rail, each grinder head including its own individual electric driving motor, a similar plurality of pressure responsive means separately associated with the respective grinder heads for vertically adjusting and partially counterbalancing the respective heads, relatively low pressure fluid source means communicating with said pressure responsive means and influencing same to counter- '8 balance less than the entire weight of its associated grinder head, and an adjustable regulating valve interposed between each said source and its associated pressure responsive means for individually adjusting the pressure of fluid flowing from each said source to its associated pressure responsive means.

6. The combination of claim 5 including means for selectively admitting fluid to all of said pressure responsive means at a sufiiciently high pressure to raise said grinder heads from the rail.

7. The combination of claim 5 including ammeters individually in circuit with the respective electric driving motors of the grinder heads.

8. A rail grinder comprising a truck adapted for movement along a rail, a plurality of grinder heads supported by said truck for substantially vertical movement into and out of operative engagement with the rail, each said head having its own electric driving motor, a similar plurality of hydraulically actuated means separately associated With the respective grinder heads for vertically adjusting and for partially counterbalancing the weight of each such grinder head, an enclosed oil reservoir normally communicating with each such hydraulically actuated means, a high pressure air manifold including lines normally communicating with the respective oil reservoirs, manually adjustable pressure regulators interposed in said lines for reducing the air pressure and maintaining it constant as the air passes to said reservoirs, and ammeters in circuit with the respective driving motors for indicating the loads imposed on the respective motors incident to regulation of the grinding pressure of the several grinder heads.

9. A rail grinder comprising a truck adapted for movement along a rail, a plurality of grinder heads supported by said truck for substantially vertical movement into and out of operative engagement with the rail, each said head having its own electric driving motor, a similar plurality of hydraulically actuated means separately associated with the respective grinder heads for vertically adjusting and for partially counterbalancing the weight of each such grinder head, an enclosed oil reservoir normally communicating with each such hydraulically actuated means, a high pressure air manifold including lines normally communicating with the respective oil reservoirs, manually adjustable pressure regulators interposed in said lines for reducing the air pressure and maintaining it constant as the air passes to said reservoirs, and manually controllable means for selectively conveying air at full pressure from said high pressure manifold to said reser- VOll'S.

10. A rail grinder comprising a truck movable along a rail, a plurality of grinder heads guided on said truck for generally vertical movement into and out of engagement with the rail, a similar plurality of pressure responsive means separately associated with the respective grinder heads for vertically adjusting and for partially counterbalancing the respective heads, a high pressure fluid source, a similar plurality of shuttle valves each communicating with one of said pressure responsive means, means establishing two separate paths of communication between said high pressure fluid source and each said shuttle valve, individual regulable pressure reducers interposed in one said path to each shuttle valve, a control valve controlling the said paths and adapted to place same selectively in communication either with said high pressure fluid source or with an exhaust passage.

ll. In a mechanism of this character described, the combination comprising a differential pressure valve, including a cylindrical valve casing having a low pressure air inlet port at one end thereof, an alternately functioning high pressure air inlet port and exhaust port at its opposite end, and a port through its cylindrical wall medially between said first mentioned ports, a valve body freely movable in said casing responsive to pressure differential on opposite sides thereof between operative positions on opposite sides of said medial port, to establish communication between said medial port and whichever of the other ports provides entry of air under the higher pressure, a source of air of relatively low pressure in constant communication with said low pressure port, a source of air at relatively high pressure, an exhaust outlet, and valve controlled means for selectively connecting said alternately functioning port either to said high pressure air source or to said exhaust outlet, whereby admission of air to the valve from said high pressure source will move the valve body to permit passage of the high pressure air through said medial port, and subsequent exhaust of air through said alternately functioning port will permit the low pressure air source to move the valve body to establish communication between said medial port and the low pressure source.

12. The combination of claim 11 including an enclosed hydraulic reservoir, hydraulic mechanism operatively connected to said reservoir for actuation responsive to changes of pressure in said reservoir, and means establishing communication between said reservoir and said medial port, whereby air supplied through said medial port may actuate said hydraulic mechanism.

13. A rail grinder comprising a truck movable along a rail, a grinder head guided on said truck for generally vertical movement, fluid pressure means for raising said grinder head out of operative engagement with the rail, 21 source of fluid under pressure connected to said fluid pressure means for applying actuating pressure thereto, valve means interposed between said fluid pressure source and the fluid pressure means, and governor controlled means for opening said valve means responsive to decrease of the speed of movement of said truck below a predetermined rate, whereby to cause raising of the grinder head.

14. A rail grinder comprising a truck movable along a rail, a plurality of grinder heads guided on said truck for generally vertical movement, fluid pressure means individually associated with the respective grinder heads for raising said heads out of operative engagement with the rail, a source of fluid under pressure connected to each of said fluid pressure means for applying actuating pressure thereto, a master control valve disposed to simultaneously control the passage of fluid from said pressure source to each of said fluid pressure means, and speed responsive means for opening said valve when the speed of said truck along this rail is below a predetermined minimum.

15. A fluid pressure control system comprising a source of fluid at relatively high pressure, a by-pass line, a plurality of diflerential valve circuits separately connected to and establishing communication between said source and said by-pass line, each said circuit comprising a differential pressure valve having opposed inlet ports connected with said source and said by-pass line respectively, said difierential valve being actuated by differences in the fluid pressure entering its respective inlet ports, to permit the passage therethrough of the fluid under the higher pressure, a pressure regulating valve disposed in each said circuit between said source and the difierential valve to cause a drop in pressure of the fluid entering the valve from said source, a master control valve directly operatively connected between said source and the by-pass line for selectively connecting said line either with said source or with an exhaust outlet in said control valve, whereby the pressure acting on the valve through the by-pass line may be either greater or less than that of the fluid acted upon by said reducing valve.

16. The combination of claim 15 including a reversing valve in each said circuit for relatively transposing the connections of said source and said by-pass to the re spective inlet ports.

17. In a mechanism of the character described, a differential pressure valve comprising a cylindrical valve casing having fluid inlet ports at opposite axial ends thereof, a medial port through the cylindrical wall of said casing between said inlet ports, and a valve body freely axially slidable in said casing between operative positions on opposite sides of said medial port responsive to pressure differentials on opposite sides of said valve body, in combination with means for admitting fluid at a constant pressure through one of said opposed fluid inlet ports, and manually controllable means for selectively admitting fluid at a relatively higher pressure through the other of said opposed ports.

18. The combination of claim 17 wherein said manually controllable means includes a valve disposed to selectively establish communication between said other port and either the atmosphere or a source of fluid at said relatively higher pressure.

19. The combination of claim 17 wherein said manually controllable means includes a source of air at relatively high pressure, connecting means including a pressure regulator establishing constant communication between said source and said one port, and means including a manually controllable valve for selectively establishing communication between said other port and either the atmosphere or said high pressure air source.

References Cited in the file of this patent UNITED STATES PATENTS 1,723,112 Wolever Aug. 6, 1929 2,018,411 Miller Oct. 22, 1935 2,035,154 Faries et a1. Mar. 24, 1936