neutral position when adequate pilot pressure is avail- be chosen manually. With the pilot valve 134 in the able, the brake saver valve 46 is automatically actuated position shown, pilot pressure is not applied to the to supply pilot fluid to breake releasing means 40, 42. valve 128 from the pilot system, so that open communiThus, the brake releasing means is normally responsive cation is provided between the juncture 120 and tank
to release the brake simultaneously with actuation of a 5 14. Movement of the pilot valve 134 to the other posidrive control valve. tion thereof applies pilot pressure to the valve 128 so
In the subject arrangement, as an example, the that communication is blocked between the juncture brakes require a minimum of 250 psi to be released 120 and tank 14.
completely. However, the pilot system will function In the operation of such system, the drive motors 26,
even ifthe supply pressure falls below 250 psi. Thus, 10 28 are operated in accordance with the above procewith the vehicle travelling under these conditions, the dure.
brakes will not fully release. This results in the brakes Assuming, for example, that the drive motors 26, 28 dragging and failing prematurely. However, the subject of the vehicle are not being operated, the distributor brake saver circuit is operative to prevent this. valve 104 may be shifted by appropriate use of the pilot
Upon the operator activating either of valves 48, 50, 15 valve 108, whereby communication is provided bepilot pressures is directed to pilot control valves 58, 60 tween the swing pump 100 and swing motor 106 for by way of conduits 64, 66, 68, 70. Two pairs of pilot operating the swing motor 106. With the swing motor lines 72 and 74 and 76 and 78 connect control valves 106 being operated, fluid communication between the 58, 60 to the main control valves 22 and 20, respec- swing pump 100 and the juncture 120 is blocked, as
tively. A three-way check or shuttle valve 80 intercon- 20 will be seen. If the swing motor 106 is not to be opernects the conduits 64, 68 by conduits 82, 84 to direct ated, fluid pressure from the pump 100 is relieved pilot pressure through a conduit 86 to the brake saver through the line 116, through the main valve 128 and valve 46 regardless of which of the valves 58, 60 is to tank 14, the main valve 128 being normally posiactuated. tioned as shown due to the selective positioning of the
Pressurized fluid from pump 36 is directed by way of 25 two-position pilot valve 134. Thus, the fluid swing lines 38, 52, 88 to shift the brake saver valve 46 right- motor 106 may selectively be placed in a driving or a ward against its spring. This permits pressurized fluid in non-driving state.
conduit 86 from the drive and steering pilot control Assuming that the drive motors 26, 28 are being system portion of the circuit to be directed by conduit operated in accordance with the above description, but
90 to shift the brake valve 44 against its spring and 30 with the two-positioning of the distributor valve 104 as permit pilot pressure in line 52 to be directed by con- shown, resulting in non-driving of the swing motor 106, duit 92 to the brake actuating means 40, 42, for disen- still provides that fluid pressure from the swing pump gaging the brake. A pilot pressure of at least 260 psi in 100 is released through main valve 128 to tank 14. conduit 88 is required to shift the brake saver valve 46 Again, normal swing operation of the swing motor 106
and communicate the pilot fluid pressure to shift valve 35 will occur upon appropriate actuation of the pilot valve 44 to provide communication of the pilot fluid to brake 108. If it is desired that swing pump fluid be directed to actuating means 40, 42, to overcome the spring pres- the drive motors 26, 28, the two-position pilot valve sure and release the brake. In the event that the pilot 134 is moved to its second, lower position to block off system supply pressure drops below 260 psi, the brake the juncture 120 form the tank 14. Then, with the
saver valve 46 shifts leftward under influence of its 40 distributor valve 104 in the position shown, blocking spring and vents line 90 to tank 14 via line 94. This communication between the swing pump 100 and permits valve 44 to shift to the left (to the position swing motor 106, fluid from the pump 100 is directed shown) and connects line 92 to tank 14 by way of line through conduit 116 to juncture 120 and into line 18 96, thus venting fluid from the releasing cylinders of and line 118 to the motors 26, 28, to increase overall
the brake actuating means 26, 28. 45 vehicle travel speed.
Referring now to the swing portion of the circuit of It is to be noted that, with the main valve 128 in a the drawing, a pump 100 draws fluid from the reservoir blocking position, if the distributor valve 104 is shifted 14 and supplies such fluid by way of line 102 to a dis- so that communication is provided between the swing tributor valve 104. The pump 100 is the source of fluid pump 100 and swing motor 106, communication be
for powering the swing motor 106 with distributor 50 tween the swing pump 100 and conduit 116 is blocked, valve 104 operative to direct fluid thereto. A pilot valve Thus, it will be seen that the system is designed to 108 is operatively connected with the distributor valve provide that the fluid from the fluid swing pump 100 104, to provide selective positioning of such distributor may be selectively directed to the drive motors 26, 28 valve 104, by means of lines 110, 112, 114. A conduit only with communication between the swing pump 100
116, connects the valve 104 and line 18, and a line 118 55 and swing motor 106 being blocked by the distributor also communicates the line 16 adjacent the pump 10 valve 104. As soon as the valve 104 is shifted in order and the conduit 116, the conduit 116, line 18 and line to provide operation of the swing motor 106, such 118 coming together at a common juncture 120. One- swing motor 106 will indeed operate, and fluid from the way check valves 122,124 are included in the lines 18, swing pump 100 is no longer directed to the motors 26,
118 respectively to block any possibility of the pump 60 28. Thus, an override feature is provided in association pumping fluid through the conduit 116 toward the with the swing pump 100 and motor 106, it being asvalve 104. Yet another line 126 communicates the sured that operation of the pilot valve 108 will achieve juncture 120 and a main valve 128, and a line 130 proper operation of the swing motor 106 as desired, communicates the main valve 128 with line 132 which With the system in the state wherein the two-position
in turn communicates with reservoir or tank 14. A 65 pilot valve 134 is in its second, lower position, and with two-position pilot valve 134 is operatively connected the distributor valve 104 in the position shown, the with the main valve, and includes detent means 136 for valve 128 is in a blocking position, and the pump 100 is maintaining the selected position thereof, which may in condition to supply fluid to the motors 26, 28 as