a mobile hospital stretcher which embodies the present invention is shown at 10 in fig1 . the stretcher 10 includes a base 11 which is movably supported by four casters having wheels 12 , and has supported on top of the base 11 two upright hydraulic jacks or cylinders 16 and 17 which have respective upwardly extending piston rods 18 and 19 . the stretcher 10 includes a support frame 22 which is supported by and pivotally coupled to the upper end of each of the piston rods 18 and 19 . the support frame 22 supports a mattress 23 , which has an upwardly facing support surface 24 for a patient 25 . the base 11 of the stretcher 10 has three foot pedals , one of which is shown at 27 , and the three foot pedals are used to manually control the hydraulic cylinders 16 and 17 in a manner discussed in more detail later . the stretcher 10 also has an electric control panel 28 mounted at one end of the frame 22 , the control panel 28 being used to electrically control the hydraulic cylinders 16 and 17 in a manner described in more detail later . power for the circuitry associated with electric control panel 28 is obtained from a standard 110 volt wall outlet through a standard line cord 31 and plug 32 . it will be recognized that the bed could also have a similar control panel at the opposite end , but to avoid redundancy here only a single such panel is shown and described . the hydraulic circuit which controls the hydraulic cylinders 16 and 17 is shown in detail in fig2 . the housings of the hydraulic cylinders 16 and 17 enclose respective upright cylindrical chambers 36 and 37 which each have a respective piston 38 or 39 vertically movable disposed therein . the piston rods 18 and 19 are respectively secured to and extend upwardly from the pistons 38 and 39 . each of the pistons 38 and 39 has extending around it a respective annular seal 41 or 42 , which slidably sealingly engages the side walls of the associated chamber 36 or 37 . a drain conduit 43 provides fluid communication between the upper end of the chamber 36 in hydraulic cylinder 16 and a fluid reservoir 47 . to the extent that any hydraulic fluid leaks from the lower portion of chamber 36 up past the annular seal 41 , it can flow out through the drain conduit 43 to reservoir 47 as the piston 38 moves upwardly . a similar drain conduit 44 is provided between chamber 37 of hydraulic cylinder 17 and the reservoir 47 . a bypass conduit 48 communicates with chamber 36 of hydraulic cylinder 16 at a vertical location which is just below the underside of piston 38 when piston 38 is in its uppermost position , as shown in fig2 . the bypass conduit 48 communicates , through drain conduit 43 , with the reservoir 47 . when the piston 38 is below its uppermost position , the bypass conduit 48 is blocked by the piston so that no fluid from the lower portion of chamber 38 can flow into bypass conduit 48 , whereas when the piston 38 is in its uppermost position the bypass conduit 48 communicates with the lower portion of chamber 36 so that fluid from chamber 36 can flow through bypass conduit 48 and conduit 43 to the reservoir 47 . an equivalent bypass conduit 49 is provided for the hydraulic cylinder 17 . a limit switch 51 is mounted on top of the housing of hydraulic cylinder 16 , and is mechanically actuated by the bed frame 22 when the piston 38 of hydraulic cylinder 16 has dropped to its lowermost position . a similar limit switch 52 is provided on top of hydraulic cylinder 17 , and is mechanically actuated by the bed frame 22 when the piston 39 of hydraulic cylinder 17 has dropped to its lowermost position . the limit switches 51 and 52 are connected to a circuit which will be described in more detail later in association with fig3 . a control conduit 53 communicates with the chamber 36 of hydraulic cylinder 16 near the lower end of chamber 36 . as described below , fluid is supplied to the chamber 36 through conduit 53 in order to cause the piston 38 to move upwardly , and fluid is drained from the chamber 36 through conduit 53 in order to permit the weight of bed frame 22 to move piston 38 downwardly . an equivalent control conduit 54 is provided for the chamber 37 of hydraulic cylinder 17 . an electrically actuated pump mechanism 56 takes fluid from the reservoir 47 , and supplies it through respective outlets 57 and 58 to the inlets of respective check valves 59 and 60 which have their outlets respectively coupled to the control conduits 53 and 54 . a manually operated pump mechanism 62 takes fluid from the reservoir 47 and supplies it through respective outlets 63 and 64 to the inlets of check valves 59 and 60 . check valves 59 and 60 permit fluid to flow from the pump mechanisms 56 and 62 through control conduits 53 and 54 to chambers 36 and 37 , but prevent fluid flow from conduits 53 and 54 back to the pump mechanisms 56 and 62 . two normally closed , electrically actuated solenoid valves 66 and 67 have inlets which are respectively connected to the control conduits 53 and 54 . the valves 66 and 67 are electrically controlled by the circuit of fig3 in a manner described in more detail later . two normally closed , manually operated valves 68 and 69 have inlets which are also respectively coupled to the control conduits 53 and 54 . as mentioned above in association with fig1 the base 11 of stretcher 10 has three foot pedals , only one of which is shown at 27 in fig1 . the other two foot pedals are shown diagrammatically at 71 and 72 in fig2 and each opens a respective one of the valves 68 and 69 when manually operated . the four valves 66 - 69 are each a conventional and commercially available part , and their internal structure is therefore not described in detail here . the outlets of the two valves 66 and 68 are connected to each other and to an inlet of a manually adjustable throttle valve 73 , and in a similar manner the outlets of the valves 67 and 69 are connected to each other and to the inlet of a manually adjustable throttle valve 74 . the outlets of the throttle valves 73 and 74 are connected to each other and to the inlet of a conventional and commercially available filter unit 76 , the outlet of the filter unit 76 communicating with the reservoir 47 . a manually adjustable pressure regulating valve 78 has its inlet connected to the outlets 57 and 63 of pump mechanisms 56 and 62 , and has its outlet connected to the inlet of filter 76 . a similar pressure regulating valve 79 has its inlet connected to the outlets 58 and 64 of pump mechanisms 56 and 62 , and has its outlet connected to the inlet of filter 76 . if the outlet pressure produced by either of the pump mechanisms 56 and 62 exceeds a manually preset pressure value at either of valves 78 and 79 , that valve will bleed fluid from the pump outlet to the filter 76 so that the fluid pressure ultimately supplied through check valve 59 or check valve 60 does not exceed the preset pressure value of the associated regulating valve 78 or 79 . the regulating valves 78 and 79 are conventional and commercially available parts , and their internal structure is therefore not described here in detail . the manually operated pump mechanism 62 includes two mechanically operated pumps 83 and 84 which are conventionally and commercially available parts , the pumps 83 and 84 drawing fluid from reservoir 47 through respective check valves 86 and 87 , and supplying fluid through respective pump check valves 88 and 89 to the respective outlets 63 and 64 of pump mechanism 62 . the pumps 83 and 84 are both coupled to and simultaneously operated by the foot pedal shown at 27 in fig1 and 2 . the electrically actuated pump mechanism 56 includes two conventional and commercially available pump units 91 and 92 , which each draw fluid from the reservoir 47 and supply it through respective pump check valves 93 and 94 to the respective outlets 57 and 58 of pump mechanism 56 . in the preferred embodiment , the pumps 91 and 92 are parts obtained commercially from mechanical tool and engineering co ., in particular model no . s201013381 . the pumps 91 and 92 have rotatable drive shafts which are coupled together and driven simultaneously by a common electric motor 96 , the motor 96 being selectively electrically actuated by the electrical circuit which is shown in fig3 and described below . when the electrical pump mechanism 56 is deactuated and the manual pump mechanism 62 is being operated , the pump check valve 93 prevents fluid supplied to outlet 63 by pump 83 from flowing through pump 91 to the reservoir 47 , and the pump check valve 94 prevents fluid supplied to outlet 64 by pump 84 from flowing through pump 92 to the reservoir 47 . similarly , when the electrical pump mechanism 56 is actuated and the manual pump mechanism 62 is not being operated , the pump check valve 88 prevents fluid supplied to outlet 57 by pump 91 from flowing through pump 83 to reservoir 47 , and the pump check valve 89 prevents fluid supplied to outlet 58 by pump 92 from flowing through pump 84 to reservoir 47 . turning to fig3 the electrical control panel 28 includes four momentary push button switch units which are respectively labeled up , down , rev trend and trend . trend refers to the trendelenburg position , in which a patient is inclined so that his head is lower than his feet ( as in fig1 ), whereas rev trend refers to the reverse trendelenburg position in which the patient is inclined so that his feet are lower than his head . the up switch unit includes a single switch 99 , the down switch unit includes a single switch 100 , the rev trend switch unit is a conventional double pole single throw device having two separate switches 101 and 102 which operate simultaneously , and the trend switch unit is also a conventional double pole single throw device having two switches 103 and 104 which also operate simultaneously . switch 99 has one terminal connected to ground and the other terminal connected to the cathode of a diode 106 and one end of a pull - up resistor 107 . the switches 102 and 104 each have one terminal connected to ground and the other terminal connected to the cathode of a respective diode 108 and 109 and one end of a respective pull - up resistor 112 or 113 . the switch 100 has one terminal connected to ground and the other terminal connected to the cathodes of two diodes 116 and 117 and one end of a pull - up resistor 118 . the switch 101 has one terminal connected to ground and the other terminal connected to one end of limit switch 51 , the other end of limit switch 51 being connected to the cathode of a diode 121 and one end of a pull - up resistor 122 . the switch 103 has one terminal connected to ground and the other terminal connected to one end of limit switch 52 , the other end of limit switch 52 being connected to the cathode of a diode 123 and one end of a pull - up resistor 124 . the pull - up resistor 107 has its upper end in fig3 connected to a source of a constant positive d . c . voltage v , and the same is true of the other five pull - up resistors 112 , 113 , 118 , 122 and 124 in fig3 . the anodes of diodes of 106 , 121 and 123 are connected at 131 to each other and to a control input of a drive circuit 127 which can selectively energize the motor 96 of the pump mechanism 56 of fig2 in dependence on the state of its control input . the anodes of diodes 116 and 108 are connected at 132 to each other and to a control input of a drive circuit 128 , and the anodes of diodes 117 and 109 are connected at 133 to each other and to the control input of a drive circuit 129 , the drive circuits 128 and 129 respectively selectively energizing the solenoid valves 66 and 67 for the hydraulic circuit of fig2 in dependence on the state of the control signals at their control inputs . those of ordinary skill in the art are familiar with the type of circuitry commonly used for the drive circuits 127 - 129 , and the drive circuits 127 - 129 are therefore are not shown in detail . each might , for example , include a conventional relay , the coil of which is controlled by the signal present at the control input of the drive circuit , and the contact of which couples a conventional source of electrical power to the output of the drive circuit when the contact is closed . referring to fig2 the manner in which the hydraulic system can be manually controlled will be explained first . it is assumed that the pistons 38 and 39 are each initially in their lowermost positions within the hydraulic cylinders 16 and 17 . if the foot pedal 27 is repeatedly pressed , the pumps 83 and 84 will each draw fluid from the reservoir 47 and eject it into a respective outlet 63 or 64 , so that hydraulic fluid flows through each of the check valves 59 and 60 and into the lower portion of chambers 36 and 37 , causing pistons 38 and 39 to simultaneously move upwardly , which in turn causes the support frame 22 to move upwardly while remaining horizontal . when the operator stops pushing the pedal 27 , the pistons 38 and 39 will each stop at their current vertical level . if the operator continues to press the pedal 27 until the pistons 38 and 39 each reach their uppermost position , the openings to bypass conduits 48 and 49 will be exposed and thus any additional fluid flowing into the chambers 36 and 37 will flow out through the bypass conduits 48 and 49 to the reservoir 47 , so that there is no excess pressure built up in the hydraulic cylinders 16 and 17 . the foot pedals 71 and 72 for the normally closed manual valves 68 and 69 are preferably located adjacent each other so that an operator can step on them simultaneously . when an operator does step on them simultaneously , the valves 68 and 69 will simultaneously open , and fluid will flow from chamber 36 through conduit 53 , valve 68 , throttle 73 and filter 76 to the reservoir 47 , while fluid also flows from the chambers 37 through conduit 54 , valve 69 , throttle 74 and filter 76 to reservoir 47 . the throttles 73 and 74 are preferably adjusted so that the fluid flow rates through them are substantially identical , as a result of which the pistons 38 and 39 will drop at substantially the same rate so that the frame 22 will move vertically downwardly without any change in inclination . if the operator wishes to incline the frame 22 in the manner shown in fig1 so that the patient &# 39 ; s head is lower than his feet , the operator manually presses only the foot pedal 72 in fig2 so that valve 69 is opened and fluid escapes only from the chamber 37 and only the piston 39 drops downwardly , the position of the piston 38 remaining unchanged . alternatively , if the operator wished to achieve an inclination opposite that shown in fig1 namely where the patient &# 39 ; s feet are lower than his head , the operator would manually press only the foot pedal 71 in fig2 so that valve 68 would permit the escape of fluid only from chamber 36 in order to cause only the piston 38 to move downwardly , the piston 39 remaining in its current position without any change . if the frame 22 is already inclined and then the foot pedals 71 and 72 are pressed simultaneously , fluid will escape through valves 68 and 69 from both of the chambers 36 and 37 , so that the pistons 38 and 39 both move downwardly and the bed frame 22 moves downwardly without any change in its angle of inclination . of course , one of the pistons which is lower than the other will eventually reach its lowermost position and stop moving downwardly , after which the other will continue downwardly if the operator continues to press the associated foot pedal , the result of which will be that the frame 22 will gradually return to a horizontal orientation . at the hydraulic level , the electrically actuated pump mechanism 56 and the electrically actuated valves 66 and 67 correspond directly in function to the manually operated pump mechanism 62 and the manually operated valves 68 and 69 . in particular , if the motor 96 is actuated , the pumps 91 are 92 are both driven and respectively supply fluid through check valves 59 and 60 so that the pistons 38 and 39 both move upwardly simultaneously . if the valve 66 is electrically actuated , fluid can escape from chamber 36 so that piston 38 moves downwardly , whereas if the valve 69 is electrically actuated fluid can escape from chamber 37 so that the piston 39 moves downwardly . however , the manner in which the electrically actuated valves 66 and 67 and electrically actuated pump mechanism 56 are actuated is a little different from the manner in which the manually operated valves 68 and 69 and pump mechanism 62 are actuated , due to the presence of limit switches 51 and 52 and the circuit shown in fig3 . more specifically , when an operator presses and holds the switch unit labeled up on control panel 28 , the switch 99 is closed and grounds the cathode of diode 106 , pulling the control input 131 of drive circuit 127 to a lower voltage , which causes the drive circuit 127 to actuate the motor 96 for pump mechanism 56 of fig2 . accordingly , the pistons 38 and 39 simultaneously move upwardly , and each continues to move upwardly until it reaches its uppermost position or until the switch 99 opens , whichever occurs first . if the switch unit labeled down is pressed , the switch 100 closes and connects the cathodes of diodes 116 and 117 to ground , thereby pulling down the voltages at the control inputs 132 and 133 of the drive circuits 128 and 129 , so that the drive circuits 128 and 129 respectively electrically actuate the solenoid valves 66 and 67 of fig2 thereby opening these valves so that fluid escapes from each of the chambers 36 and 37 in the hydraulic cylinders 16 and 17 . the pistons 38 and 39 thus move simultaneously downwardly , and each continues to move downwardly until it reaches its lowermost position or until the switch 100 opens , whichever occurs first . the switch labeled rev trend in fig3 is pressed when an operator wishes to incline the frame so that the patient &# 39 ; s feet are lower than his head , whereas the switch unit labeled trend is pressed when the operator wishes to incline the frame so that , as shown in fig1 the patient &# 39 ; s head is lower than his feet . when the switch unit rev trend is pressed , the switches 101 and 102 are simultaneously closed . the switch 102 forces the cathode of diode 108 to ground , thereby causing drive circuit 128 to energize solenoid valve 66 of fig2 so that fluid escapes from the chamber 36 of hydraulic cylinder 16 and the piston 38 drops , the piston 39 of hydraulic cylinder 17 remaining stationary . thus , the patient &# 39 ; s feet begin to move downwardly relative to his head . if the piston 38 reaches its lowermost position and the operator continues to press the rev trend switch unit so that switches 101 and 102 remain closed , the engagement of frame 22 with limit switch 51 will cause limit switch 51 to close , and switches 101 and 51 will thus ground the cathode of diode 121 and cause the drive circuit 127 to energize motor 96 for the pump mechanism 56 of fig2 . thus , pumps 91 and 92 in fig2 will begin supplying fluid through check valves 59 and 60 . the fluid supplied through check valve 60 to chamber 37 will cause the piston 39 to begin moving upwardly . meanwhile , since the closed switch 102 is still keeping the valve 66 open , fluid supplied by pump 91 through check valve 59 will flow through valve 66 , throttle 73 and filter 76 back to the reservoir 47 , and will not flow into chamber 36 and will not cause piston 38 to move upwardly . consequently , inclination of the frame 22 in the desired manner will continue to occur , the patient &# 39 ; s feet becoming progressively lower relative to the patient &# 39 ; s head . when the rev trend switch unit is released by the operator , the bed frame 22 stops at and remains in its current angle of inclination . if the operator actuates the trend switch unit , a sequence which is basically a mirror image of that just described will occur . in particular , the valve 67 will initially be open so that fluid escapes from chamber 37 and piston 39 moves downwardly , and if piston 39 reaches it lowermost position the limit switch 52 will be actuated and energize the motor 96 so that pump mechanism 56 supplies fluid to chamber 36 and moves piston 38 upwardly , the open valve 67 preventing fluid from pump mechanism 56 from moving piston 39 upwardly . although a preferred embodiment of the present invention has been described in detail for illustrative purposes , it will be recognized that variations or modifications of the disclosed apparatus , including the rearrangement of parts , lie within the scope of the present invention .
a mobile hospital stretcher includes a movably supported base , and two spaced hydraulic cylinders on the base which vertically movably support a support member having an upwardly facing support surface . separate control systems are provided for the hydraulic cylinders , one of which is electrically powered and the other of which is mechanically powered . the electrically powered system includes an electrically actuable valve for selectively bleeding fluid from one of the cylinders , an electrically actuable pump for supplying fluid to the other cylinder , a limit arrangement which produces a signal when the first cylinder is fully retracted , a manually operable switch for electrically actuating the valve , and an arrangement responsive to the presence of the first signal during actuation of the switch for electrically actuating the pump .