US3038439A - Relay control system and indicating relay therefor - Google Patents

Description

June 12, 1962 H. w. MARTIN ETAL RELAY CONTROL SYSTEM AND INDICATING RELAY THEREFOR Filed March 19, 1959 START/N6 All? m H E INVENTORS HENRY W. MART/N B4$RTHUR J- JOHNSON a M W 7 k 7 7 N 9 9 W 9 m5 E W ms 9 o w m LP m R U E T H H M T V 0 F a 0 w H. M .w. a m 7 FEW THE/R ATTORNEYS 3,038,439 Patented June 12, 1982 hce RELAY CONTROL SYSTEM AND INDltIATlNG RELAY THEREFOR Henry W. Martin and Arthur J. Johnson, Houston, Tex, assignors, by mesne assignments, to Arnot Controls Corporation, Richmond, Califi, a corporation of Qaiifornia Filed Mar. 19, 1959, Ser. No. 800,552 12. Claims. (til. 116-117) Our invention relates to control systems and more particularly to a relay control system and indicator relay therefor.

The invention, while of a general application, is particularly applicable in protecting and controlling the operation of internal or the like combustion engines such as heavy diesel engines. In many installations employing such diesel engines, the engines operate unattended for substantial periods of time, and it is desirable that upon the occurrence of a condition such as excessively high temperature, loss of oil pressure, or excessive speed, any one of which could result in considerable damage to the engine, the engine should automatically shut down.

Heretofore control systems employed for this purpose were primarily electrical in character and such could in and of themselves prove dangerous, due to the presence of arcing contacts or generation of sparks in the function ing thereof.

Further, in the event of a shut down, the specific cause of the trouble is not apparent from observation and the service man therefore must check the entire engine for the specific source of the trouble.

Among the objects of our present invention are:

(1) To provide a novel and improved control system employing mechanical relays;

(2) To provide a novel and improved control system employing mechanical relays and capable of responding to any one of a number of possible situations apt to occur in apparatus under control of such system;

(3) To provide a novel and improved control system employing mechanical relays adapted to respond to situations developing in apparatus under control and at the same time designate or indicate the specific condition which caused such response of the control system;

(4) To provide a novel and improved mechanical relay;

To provide a novel and improved mechanical relay which is pressure responsive;

(6) To provide a novel and improved mechanical relay having visual indicating means incorporated therein; and

(7) To provide a novel and improved mechanical relay which is pressure responsive and includes visual indicatin g means therein.

Additional objects of our invention will be brought out in the following description of a preferred embodiment of the same taken in conjunction with the accompanying drawings wherein:

FIG. 1 is a view in section through a mechanical relay of the present invention taken in a plane through the longitudinal axis thereof;

FIG. 2 is a view depicting a typical control system of the present invention, utilizing a plurality of mechanical relays as illustrated in FIG. 1;

FIG. 3 is a View in section depicting basic construction of a pressure operated valve employed in the system of FIG. 2 such section being in a plane through the longitudinal axis thereof.

FIGURE 4 is an enlarged view in section of a compo nent appearing in the system of FIGURE 2.

A knowledge of the indicating relay of our present invention as depicted in FIG. 1, is necessary to an understanding of the indicating relay control system illustrated in FIG. 2 and accordingly will be described in detail first.

Referring to the drawings, the indicating relay 1 of our present invention comprises a casing 2 having an input pressure opening 3 located adjacent one end 4 of the casing, and a pressure release opening 5 preferably located in the remote end 6 of the casing.

In addition to these two openings, the casing is also provided with an output pressure opening 7 and a vent opening 9 preferably located intermediate the pressure release and input pressure openings, with the output pressure opening closer to the input pressure opening.

Interiorly of the casing, approximately one-half 10 of the casing 2 adjacent the release pressure opening 5, is of larger diameter than the remaining portion.

Slidably disposed within the casing is a hollow piston 13. This piston is open at that end 14 facing the inlet pressure opening 3, While at its other end, the piston is fitted with a piston ring 15 slidably engaging the larger internal diameter section 10 of the casing, and an orifice plug 17 axially of the piston.

Movement of the piston in the direction of the inlet pressure opening is limited by an O ring 19 about the piston engaging a sloping shoulder 20 on the interior wall of the casing, such 0 ring in addition functioning as a seal between the piston and casing. In the position of the piston 13 as determined by this 0 ring, the end 14 toward the input pressure opening 3, intercepts such opening and accordingly will always be exposed to the input pressure opening.

Gas or other fluid medium under pressure that enters the casing through the input pressure opening 3, may exert pressure directly against the proximate end rim 23 of the piston and the side of the orifice plug 17 facing interiorly of the piston, such surfaces providing a surface area against which such gas or other fluid medium may exert pressure tending to drive the piston in the direction of the pressure release opening 5.

By the same token, such gas on passing through the orifice plug 17, if permitted to build up and equaize in the chamber 25 formed by this end of the piston and the casing, will exert a pressure in the opposite direction against this end of the piston made up for the most part of the piston ring 15 and plug 17, thus in a direction tending to drive the piston toward the input pressure opening end 4 of the casing.

The aforementioned construction of the piston thus presents to the input pressure opening 3, two opposing surface areas. Being that the surface area presented by the pressure release end of the piston is greater than that offered by the end rim 23 and plug 17, such piston, with the pressure release opening blocked, will. be driven toward the input pressure opening end 4 of the casing to the position determined by the O ring 19.

Upon release of pressure from the chamber 25, as through unblocking of the pressure release opening 5, the piston then will be driven toward the release opening end of the casing.

In addition to the foregoing, the piston is formed with a reduced section 29 adjacent the input pressure opening end 14, such reduced section being of a length suflicient to provide a chamber 31 connecting the input pressure opening 3 to the output pressure opening 7 when the G ring 19 is in sealing engagement with the sloping shoulder.

With the piston shifted in the opposite direction toward the pressure release opening 5, the end 14 of the piston should move beyond the edge of the input pressure opening to valve off such opening from the output pressure opening 7 while the chamber 31 formed by the reduced section of the piston, should couple the output pressure opening 7 with the vent opening 9.

To indicate which of the aforementioned positions of the piston prevails at any time, a window 37 is provided in the casing in that portion 19 of larger internal diameter, while the piston is provided with suitable indicating symbols capable of being viewed through the window with the piston in said positions. Such symbols in the present instance may involve a pair of adjacently disposed bands 41, 43 on or about the piston, one of a color such as green to designate a condition indicative of normalcy, while the other will be of a different and contrasting color such as red to designate a condition indicative of abnormalcy or danger.

From the foregoing description of the indicating relay of the present invention, it will be apparent that with the pressure release opening blocked, gas under pressure introduced through the input pressure opening 3 will in part fill the piston and the end chamber adjacent the pressure release opening, and as the pressure equalizes throughout the space thus occupied, the greater piston surface area facing the chamber will cause movement of the piston 13 in the direction of the shoulder 20 and to the point of engaging such shoulder by the O ring 19.

A portion of the inflowing gas under pressure will fiow through the output discharge opening 7 in the casing to be utilized at some other point in this system as will be described.

Upon, releasing the pressure in the end chamber through the pressure release opening 5, the pressure on the piston will then be predominantly in the other direction, thus causing the piston to shift toward the pressure release opening. This, as previously indicated, will disconnect the output pressure opening 7 from the input pressure opening 3 and connect it to the vent opening 9.

A typical system employing the indicating relay described above, may utilize a number of such relays ll connected in series by pipe connection 51, one from the output pressure opening 7 of the first relay of a series to the input pressure opening 3 of the next relay in the series and so on, whereby with the piston of each relay in the position of engagement of the internal shoulder 20 by the O ring 19, gas under pressure applied through the input pressure opening 3 of the first relay of the series, will have a connecting flow path through all of the relays in series. A subsequent shift of the piston 13 in any one of the relays to its opposite position will interrupt such flow path and cut off the pressure of such gas from the relays which follow in the series and vent such subsequent relays.

When utilized in a control system for a large internal combustion engine installation or the like, to protect the engine against damage from such conditions as excessive temperature, excessive speed, or low oil pressure, etc., the system includes a relay 1a, 1b, 1c, etc. for each such condition to be protected against, whereby the system is made responsive to the development of any such condition, to cut off supply of fuel to such engine and thereby cause shutdown.

Toward this end, the main fuel line 55 to the engine (not shown) includes a pressure operated main valve 57 which in response to the application of a control pressure, opens the valve and permits flow of fuel gas to the engine.

Such valve briefly includes a housing 59 (FIG. 3) having an inlet opening 61 for the fuel line and a discharge opening 63, the flow path between the two being interrupted by a partition 65 having a valve opening therethrough adapted to be opened or blocked by a valve 69 normally spring biased by a spring 70 to closed position and capable of being moved to open position against the back pressure of such spring bias, by the application of gas under pressure to a diaphragm 71, constituting a wall of a diaphragm chamber 72. In its open position, the valve 69 is adapted to automatically close a normally 4 open passage 73: between the discharge opening 63 and a vent opening 75 in the valve to which a vent line 77 is connected and which may exhaust to atmosphere. Said vent line is likewise connected to the vent opening 9 of each indicating relay in the system.

From a point '78 on the main fuel line 55 before it couples to the pressure operated main valve 57, a branch line 79 is coupled through a check valve 81 to the inlet opening of a similar pressure operated valve 85 while the output discharge opening is connected by a pipe connection S7 to the input pressure opening 3 of one of the indicating relays, namely relay 1a.

In connection with the operation of a diesel engine, certain of the desired conditions of operation are realized immediately upon starting of the engine, such as the absence of excessive speed, absence of excessive temperature, etc., while other conditions are not realized until after a brief elapsed period of time, such as development of proper lubricating pressure in the oil systern of the engine. Since, during this brief interval of time, the prevailing condition is like one which, during operation of the engine under load, would represent a danger to the machine, and through its effect on the associated relay, would cause a shutdown, such indicating relay cannot be included in the operation of the system until the normal operating condition associated therewith has been realized. Consequently, it becomes necessary, therefore, to initiate the operation of the system with an interim series involving only those relays la, 1b, 1c, etc., associated with conditions that are deemed safe operating conditions under load, and then subsequently adding to the series, those remaining indicating relays 1m, etc., upon realizing normalcy of the conditions with which they are associated.

From the pressure release opening 5 in each of the relays of the interim series, extends a pipe connection 97 to the vent line 77 and in each of these pipe connections is located a normally closed valve 99 blocking the pressure release opening of its associated relay. Control pressure, the efore, is applicable to the pressure operated main valve 57 through the branch line 79 and by way of the pressure operated valve 85, the pipe connection 8'7 and the interim series of relays 1a, 1b and 1c, etc., and a pipe connection 101 from the output pressure opening of the last relay of the interim series to the valve 57. A branch line 103 from this latter connection extends to the corresponding diaphragm chamber of a pressure operated valve of similar type.

To open the pressure control valve 85 and thus clear the control pressure flow path to the pressure operated main valve 57 in the fuel gas line, a pressure is applied from some suitable source of pressure which could conceivably be the source from which the fuel gas is obtained, but in the preferred system illustrated, such pressure may come from a high pressure air line 115, used in starting an engine, as by way of a pipe connection 117 to the diaphragm chamber of the pressure operated valve 85, such pipe connection preferably including a pressure reducer 119 by-passcd in the reverse direction by a check valve 125, a flow control assembly 127 and associated accumulator 129.

The assembly 127 involves a ball check valve 134 permitting flow to the pressure operated valve 35, and an adjustable needle valve 131 permitting restricted flow in the reverse direction.

Flow of fuel to the engine will thus occur simultaneously with the turning over of the engine for starting purposes. A manual valve 132 in the air pressure line provides for control of such simultaneous functions.

Upon closing of such valve 132, a time delay in the withdrawal of operating pressure on the valve 85 is introduced by the presence of the accumulator and needle valve, and thus serves to retain pressure thereon for a period of time comparable in duration to that required for bringing the lubricating oil pressure in the engine up to operating value.

When this occurs, the indicator relay 1m associated with the lubricating oil pressure can then be added to the interim series of relays. Inasmuch as the pressure release opening 5 of this particular relay, should also, like the others, be blocked at the time it is added in series with the others, the valve 133 in the connection 97 from such pressure release opening to the vent line 77 should, unlike the others, be a normally open valve and one which is adapted to be closed upon the oil pressure reaching normal operating value.

Upon expiration of the time delay period in the removal of pressure from the pressure operating valve 85, the flow connection from the branch line 79 to the line 87 will be closed and a new control pressure flow path established which will include the lubricating pressure indicating relay 1m and a spare relay In, if desired, which, until put to use, should have its pressure release opening 5 plugged.

Such new flow path circuit will include an extension 139 of the branch line 79 to the input opening of the pressure responsive valve 105 and a pipe connection 141 from the output opening of this valve to the input pressure opening of the first of the indicators tobe added, which in this instance is the spare indicator in, and this in turn is connected in series with the lubricating pressure associated indicator relay 1111 by a pipe connection 143 from the output discharge opening of the spare indicator relay to the input pressure opening of the lubricating pressure relay. The opening 75 of the valve 105 is not required and should be plugged.

From the output discharge opening of this latter relay 1m, a pipe connection 145 extends to the opening 75 in the pressure responsive valve 85, corresponding to the vent opening of the pressure responsive valve 57. In the manner above indicated, therefore, the added relays may be included in the series connection of relays when the conditions which they are associated with, reach normalcy.

When the engine is operating with all conditions normal, all the pressure release openings 5 of the various relays will be blocked, and an open control pressure connection will exist from the fuel line to the diaphragm of the pressure operated valve 57 in the main fuel line whereby the fuel supply to the engine will be maintained.

Upon the occurrence of a dangerous condition connected with the operation of the engine, the pressure release opening of the indicating relay associated therewith will become unblocked, which will result in a shift of the piston in that particular relay to block the control pressure line at that point, while at the same time venting the rest of the pressure line which connects to the fuel line valve 57, thus relieving the pressure on this valve and causing it to shut off the fuel supply to the engine and bring about a shutdown thereof.

With the piston in each of the indicating relays provided with the indicating symbols as previously described, it will be apparent, with the green band symbol visible during normal conditions, that upon the occurrence of a dangerous condition, the particular relay responding thereto will cause the red symbol to appear at the window, thereby immediately indicating the specific cause for such shut-down.

It will be apparent from the foregoing description of our invention in its preferred form, that the same fulfills all the objects attributed thereto, and while we have illustrated and described the preferred form of our invention in considerable detail, the same is subject to modification and alteration without departing from the underlying principles involved, and we accordingly do not desire to be limited in our protection to the specific details thus illustrated and described, except as may be necessitated by the appended claims.

We claim:

1. An indicating relay control system comprising a plurality of indicating relays, each including a casing having an input pressure opening, a pressure release opening, an output pressure opening and a vent opening intermediate said input pressure opening and said pressure release opening, a piston slidably disposed in said casing, said piston having opposing surface areas exposed to said input pressure opening, with one of said surface areas larger than the other and also exposed to said pressure release opening, whereby upon blocking said pressure release opening, said piston will move in one direction and upon unblocking of said pressure release opening said piston will move in the opposite direction, said piston being formed with a reduced section forming a chamber in said casing connecting said output pressure opening with said input pressure opening when said piston has moved in one direction and connecting said output pressure opening with said vent opening when said piston has moved in the opposite direction, means connecting said plurality of relays in series to provide a first, second, third, and last relays, said means including a pipe connection from the output pressure opening of the first relay in the series to the input pressure opening of the second relay in the series, a pipe connection from the output pressure opening of said second relay to the input pressure opening of the third relay in said series and so on to the last relay in said series, means for conveying a fluid under pressure to said series connected indicating relays, said means including a control pressure line to the input pressure opening of said first indicating relay and adapted for connection to a source of fluid under pressure, a normally closed pressure operated valve in said pressure line, and means for applying operating pressure to said valve to open same so long as operating pressure is applied, a second pressure operated valve for controlling operation of apparatus to be controlled, means applying said control pressure to said second pressure operated valve to actuate the same, said means including a pipe connection from the output pressure opening of the last indicating relay in said series to said second pressure operated valve, and valve means individual to each of said relays and normally blocking the pressure release opening of its associated relay and responsive to a predetermined change in a condition of the apparatus to be controlled, for unblocking such pressure release opening to interrupt said control pressure and vent said second pressure operated valve, and means for indicating which of said relays has functioned.

2. An indicating relay control system comprising a plurality of indicating relays, each including a casing having an input pressure opening, a pressure release opening, an output pressure opening and a vent opening intermediate said input pressure opening and said pressure release opening, a piston slidably disposed in said casing, said piston having opposing surface areas exposed to said input pressure opening, with one of said surface areas larger than the other and also exposed to said pressure release opening, whereby upon blocking said pressure release opening, said piston Will move in one direction and upon unblocking of said pressure release opening said piston will move in the opposite direction, said piston being formed with a reduced intermediate section forming a chamber in said casing connecting said output pressure opening with said input pressure opening when said piston has moved in one direction and connecting said output pressure opening with said vent opening when said piston has moved in the opposite direction, means connecting said plurality of relays in series to provide a first, second, third, and last relays, said means including a pipe connection from the output pressure opening of the first relay in the series to the input pressure opening of the second relay in the series, a pipe connection from the output pressure opening of said second relay to the input pressure opening of the third relay in said series and so on to the last relay in said series, means for conveying a fluid under pressure to said series connected indicating relays, said means including a control pressure line to the input pressure opening of said first indicating relay and adapted for connection to a source of fluid under pressure, a normally closed pressure operated valve in said pressure line, and means for applying operating pressure to said valve to open same so long as operating pressure is applied, a second pressure operated valve for controlling operation of apparatus to be controlled, means applying said control pressure to said second pressure operated valve to actuate the same, said means including a pipe connection from the output pressure opening of the last indicating relay in said series to said second pressure operated valve, valve means individual to each of said relays and normally blocking the pressure release opening of its associated relay and responsive to a predetermined change in a condition of the apparatus to be controlled, for unblocking such pressure release opening to interrupt said control pressure and vent said second pressure operated valve, and means for visually indicating which of said relays has functioned.

3. An indicating relay control system comprising a plurality of indicating relays, each including a casing having an input pressure opening adjacent one end, a pressure release opening in the other end of said casing, an output pressure opening and a vent opening intermediate said input pressure opening and said pressure release opening with said output pressure opening in proximity to said input pressure opening, a hollow piston slidably disposed in said casing, said piston having opposing surface areas exposed to said input pressure opening, with one of said surface areas larger than the other and also exposed to said pressure release opening, whereby upon blocking said pressure release opening, said piston will move in one direction toward said input pressure opening and upon unblocking of said pressure release opening said piston will move in the opposite direction toward said pressure release opening, said piston being formed with a reduced intermediate section adjacent that end facing the input pressure opening and forming a chamber in said casing connecting said output pressure opening with said input pressure opening when said piston has moved toward said input pressure opening and connecting said output pressure opening with said vent opening when said piston has moved toward said pressure release opening, means connecting said plurality of relays in series to provide a first, second, third, and last relays, said means including a pipe connection from the output pressure opening of the first relay in the series to the input pressure opening of the second relay in the series, a pipe connection from the output pressure opening of said second relay to the input pressure opening of the third relay in said series and so on to the last relay in said series, means for conveying a fluid under pressure to said series connected indicating relays, said means including a control pressure line to the input pressure opening of said first indicating relay and adapted for con nection to a source of fluid under pressure, a normally closed pressure operated valve in said pressure line, and means for applying operating pressure to said valve to open same so long as operating pressure is applied, a second pressure operated valve for controlling operation of apparatus to be controlled, means applying said control pressure to said second pressure operated valve to actuate the same, said means including a pipe connection from the output pressure opening of the last indicating relay in said series to said second pressure operated valve, valve means individual to each of said relays and normally blocking the pressure release opening of its associated relay and responsive to a predetermined change in a condition of the apparatus to be controlled, for unblocking such pressure release opening to interrupt said control pressure and vent said second pressure operated valve, and means for visually indicating which of said relays has functioned.

4. An indicating relay control system comprising a plurality of indicating relays, each including a casing having an input pressure opening adjacent one end, a pressure release opening in the other end of said casing, an output pressure opening and a vent opening intermediate said input pressure opening and said pressure release opening with said output pressure opening in proximity to said input pressure opening, a hollow piston slidably disposed in said casing, said piston having opposing surface areas exposed to said input pressure opening, with one of said surface areas larger than the other and also exposed to said pressure release opening, whereby upon blocking said pressure release opening, said piston will move in one direction toward said input pressure opening and upon unblocking of said pressure release opening said piston will move in the opposite direction toward said pressure release opening, said piston being formed with a reduced intermediate section adjacent that end facing the input pressure opening and forming a chamber in said casing connecting said output pressure opening with said input pressure opening when said piston has moved toward said input pressure opening and connecting said output pressure opening with said vent opening when said piston has moved toward said pressure release opening, means connecting said plurality of relays in series to provide a first, second, third, and last relays, said means including a pipe connection from the output pressure opening of the first relay in the series to the input pressure opening of the second relay in the series, a pipe connection from the output pressure opening of said second relay to the input pressure opening of the third relay in said series and so on to the last relay in said series, means for conveying a fluid under pressure to said series connected indicating relays, said means including a control pressure line to the input pressure opening of said first indicating relay and adapted for connection to a source of fluid under pressure, a normally closed pressure operated valve in said pressure line, and means for applying operating pressure to said valve to open same so long as operating pressure is applied, a second pressure opera-ted valve for controlling operation of apparatus to be controlled, means applying said control pressure to said second pressure operated valve to actuate the same, said means including a pipe connection from the output pressure opening of the last indicating relay in said series to said second pressure operated valve, vaive means individual to each of said relays and normally blocking the pressure release opening of its associated relay, and responsive to a predetermined change in a condition of the apparatus to be controlled, for unblocking such pressure release opening to interrupt said control pressure and vent said second pressure operated valve, and means for visually indicating which of said relays has functioned, said means including a window in the casing of each relay, a symbol on the piston in such casing viewable through said window when said piston is in that position dictated by the blocking of said pressure release opening and a dififerent symbol on said piston viewable through said window when said piston is in that position dictated by the unblocking of such pressure release opening.

5. An indicating relay comprising a casing having an input pressure opening, a pressure release opening, an output pressure opening and a vent opening intermediate said input pressure opening and said pressure release opening, a piston slidably disposed in said casing, said piston having opposing surface areas exposed to said input pressure opening, with one of said surface areas larger than the other and also exposed to said pressure release opening, whereby upon blocking said pressure release opening, said piston will move in one direction and upon unblocking of said pressure release opening, said piston will move in the opposite direction, said piston being formed with a reduced intermediate section forming a chamber in said casing connecting said output pressure opening with said input pressure opening when said piston has moved in one direction and connecting said output pressure opening with said vent opening when said piston has moved in the opposite direction, and means for visually indicating the prevailing condition of said relay.

6. An indicating relay comprising a casing having an input pressure opening, a pressure release opening, an output pressure opening and a vent opening intermediate said input pressure opening and said pressure release opening, a piston slidably disposed in said casing, said piston having opposing surface areas exposed to said input pressure opening, with one of said surface areas larger than the other and also exposed to said pressure release opening, whereby upon blocking said pressure release opening, said piston will move in one direction and upon unblocking of said pressure release opening said piston will move in the opposite direction, said piston being formed with a reduced intermediate section forming a chamber in said casing connecting said output pressure opening with said input pressure opening when said piston has moved in one direction and connecting said output pressure opening with said vent opening when said piston has moved in the opposite direction, and means for visually indicating the prevailing condition of said relay, said means being movable with movements of said piston and Within view of an observer.

7. An indicating relay comprising a casing having an input pressure opening, a pressure release opening, an output pressure opening and a vent opening intermediate said input pressure opening and said pressure release opening, a piston slidably disposed in said casing, said piston having opposing surface areas exposed to said input pressure opening, with one of said surface areas larger than the other and also exposed to said pressure release opening, whereby upon blocking said pressure release opening, said piston will move in one direction and upon unblocking of said pressure release opening said piston will move in the opposite direction, said piston being formed with a reduced intermediate section forming a chamber in said casing connecting said output pressure opening with said input pressure opening when said piston has moved in one direction and connecting said output pressure opening with said vent opening when said piston has moved in the opposite direction, and means for visually indicating the prevailing condition of said relay, said means including a window in the casing of said relay, a symbol on the piston in said casing viewable through said window when said piston is in that position dictated by the blocking of said pressure release opening and a diiferent symbol on said piston viewable through said window when said piston is in that position dictated by the unblocking of said pressure release opening.

8. An indicating relay comprising a casing having an input pressure opening adjacent one end, a pressure release opening in the other end of said casing, an output pressure opening and a vent opening intermediate said input pressure opening and said pressure release opening with said output pressure opening in proximity to said input pressure opening, a hollow piston slidably disposed in said casing, said piston having opposing surface areas exposed to said input pressure opening, with one of said surface areas larger than the other and also exposed to said pressure release opening, whereby upon blocking said pressure release opening, said piston will move in one direction toward said input pressure opening and upon unblocking of said pressure release opening said piston will move in the opposite direction toward said pressure release opening, said piston being formed with a reduced intermediate section adjacent that end facing the input pressure opening and forming a chamber in said casing connecting said output pressure opening with said input pressure opening when said piston has moved toward said input pressure opening and connecting said output pressure opening with said vent opening when said piston has moved toward said pressure release opening, and means for visually indicating the prevailing condition of said relay, said means including a window in the casing of said relay, a symbol on the piston in said casing viewable through said Window when said piston is in that position dictated by the blocking of said pressure release opening and a different symbol on said piston viewable through said window when said piston is in that position dictated by the unblocking of said pressure release opening.

9. An indicating relay comprising a casing having an input pressure opening, a pressure release opening, an output pressure opening and a vent opening intermediate said input pressure opening and said pressure release opening, a piston slidably disposed in said casing, said piston having opposing surface areas exposed to said input pressure opening, with one of said surface areas larger than the other and also exposed to said pressure release opening, whereby upon blocking said pressure release opening, said piston will move in one direction and upon unblocking of said pressure release opening, said piston Will move in the opposite direction.

10. An indicating relay comprising a casing having an input pressure opening, a pressure release opening, an output pressure opening and a vent opening intermediate said input pressure opening and said pressure release opening, a movable member disposed in said casing, said movable member having opposing surface areas exposed to said input pressure opening, with one of said surface areas larger than the other and also exposed to said pressure release opening, whereby upon blocking said pressure release opening, said movable member will move in one direction and upon unblocking of said pressure release opening, said movable member will move in the opposite direction, and means for indicating the prevailing position of said movable member.

11. An indicating fluid relay system operative from a source of fluid under pressure comprising a plurality of fluid relays, means connecting said fluid relays in a hydraulic system with said source, a control device, means connecting said control device to all said relays in fluid flow control relation, separate means individually associated with each of said relays and operatively responsive each to a predetermined change of condition of an apparatus subject to control, said relays including means for interrupting fluid flow to said control device only at the particular relay operated in response to a predetermined change of condition, and means operatively associated with said relays for indicating the particular one of the relays so operated in response to said last mentioned change.

12. The combination according to claim 11 wherein each of said relays comprises a casing having an input pressure opening, a pressure release opening, a movable pressure responsive member exposed to said input pressure opening and said pressure release opening, means for establishing a differential pressure across said pressure responsive member in one direction when said pressure release opening is blocked and in the opposite direction when said pressure release opening is unblocked, and indicator means responsive to movement of said pressure responsive member when exposed to such differential pressure, for indicating a prevailing situation in accordance with the direction of such differential pressure.

References Cited in the file of this patent UNITED STATES PATENTS

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