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A hydraulic drive system for a spreader used to distribute a road surface treatment material, such as sand or salt, across a road surface. The hydraulic drive system enables the use of pressure-compensated proportional control valves in series relationship with the auger and spinner motors, by the p

A hydraulic drive system for a spreader used to distribute a road surface treatment material, such as sand or salt, across a road surface. The hydraulic drive system enables the use of pressure-compensated proportional control valves in series relationship with the auger and spinner motors, by the provision of small restricted flow passages across the outlets of the valves.

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1. A hydraulic system for operating a feed auger and spinner of a spreader, including: first and second fluid motors for driving the feed auger and spinner, the first and second fluid motors having respective fluid inlets and outlets;a first solenoid-operated pressure-compensated proportional contro

1. A hydraulic system for operating a feed auger and spinner of a spreader, including: first and second fluid motors for driving the feed auger and spinner, the first and second fluid motors having respective fluid inlets and outlets;a first solenoid-operated pressure-compensated proportional control valve including a pressure compensating spool and having an inlet configured to receive pressurized fluid from a source thereof, a regulated flow outlet connected to the inlet of the first fluid motor, and a bypass flow outlet, whereby operation of the first valve controls the volume of flow of pressurized fluid supplied to the inlet of the first fluid motor via the regulated flow outlet with the balance of flow bypassing the first fluid motor;a second solenoid-operated pressure-compensated proportional control valve including a pressure compensating spool and having an inlet connected to the outlet of the first fluid motor and the bypass flow outlet of the first valve, a regulated flow outlet connected to the inlet of the second fluid motor, and a bypass flow outlet, whereby operation of the second valve controls the volume of flow of pressurized fluid supplied to the inlet of the second fluid motor via the regulated flow outlet of the second valve with the balance of flow bypassing the second fluid motor; andfirst and second pressure-relieving restricted flow passages respectively connected between the regulated flow outlets and bypass flow outlets of the first and second valves for preventing pressure buildup at the regulated flow outlets of the first and second valves, thereby to assure proper operation of the compensator spools of the first and second valves. 2. A hydraulic system as set forth in claim 1, wherein the first and second restricted flow passages include an orifice of no greater than about 0.020 inch in diameter. 3. A hydraulic system as set forth in claim 1, wherein the first and second restricted flow passages each is sized to accommodate the difference between leakage flow through the respective valve and the respective fluid motor. 4. A hydraulic system as set forth in claim 1, wherein the first and second restricted flow passages are sized to provide a leakage flow of about 0.12 gallons per minute. 5. A hydraulic system as set forth in claim 1, wherein the first and second restricted flow passages include an orifice of no greater than about 0.020 inch in diameter, and wherein the first and second restricted flow passages each is sized to accommodate the difference between leakage flow through the respective valve and the respective fluid motor. 6. A hydraulic system as set forth in claim 1, wherein the first and second restricted flow passages include an orifice of no greater than about 0.020 inch in diameter, and wherein the first and second restricted flow passages are sized to provide a leakage flow of about 0.12 gallons per minute. 7. A hydraulic system as set forth in claim 1, wherein the first and second restricted flow passages each is sized to accommodate the difference between leakage flow through the respective valve and the respective fluid motor, and wherein the first and second restricted flow passages are sized to provide a leakage flow of about 0.12 gallons per minute. 8. A hydraulic system as set forth in claim 1, wherein the restricted flow passage includes an orifice and a filter upstream of the orifice to prevent clogging of the orifice. 9. A hydraulic system as set forth in claim 1, further comprising a pump for providing pressurized fluid to the inlet of the first valve. 10. A hydraulic system as set forth in claim 9, wherein the pump is configured for mounting in the engine compartment of a snow-ice control vehicle for being driven off the engine. 11. A hydraulic system as set forth in claim 10, in combination with the snow-ice vehicle, and wherein the vehicle includes an engine having an engine-driven belt, and the pump is driven by the belt. 12. A hydraulic system as set forth in claim 1, in combination with the auger and spinner. 13. A method of operating a spreader assembly in a snow-ice control vehicle including an engine for effecting movement of the vehicle along a road, the spreader assembly including a pump, first and second fluid motors for driving a feed auger and spinner, respectively, and first and second solenoid-operated pressure-compensated proportional control valves, wherein each valve includes an inlet, a regulated flow outlet, and a bypass flow outlet, the method including: driving the pump off the engine of the snow-ice control vehicle;supplying pressurized fluid from the pump to the first valve;controlling the feed auger using the first valve, wherein the fluid is supplied from the first valve to the first motor via the regulated flow outlet of the first valve;supplying the fluid from the bypass flow outlet of the first valve and an outlet of the first motor to the second valve;controlling the spinner using the second valve, wherein the fluid is supplied from the second valve to the second motor via the regulated flow outlet of the second valve;supplying the fluid from the bypass flow outlet of the second valve and an outlet of the second motor to a reservoir; andusing first and second pressure-relieving restricted flow passages respectively connected between the regulated flow outlets and bypass flow outlets of the first and second valves to prevent pressure buildup at the regulated flow outlets of the first and second valves, thereby to assure proper operation of the compensator spools of the first and second valves. 14. A method as set forth in claim 13, wherein the first and second restricted flow passages include an orifice of no greater than about 0.020 inch in diameter. 15. A method as set forth in claim 13, wherein the first and second restricted flow passages each is sized to accommodate the difference between leakage flow through the respective valve and the respective fluid motor. 16. A method as set forth in claim 13, wherein the first and second restricted flow passages include an orifice of no greater than about 0.020 inch in diameter, and wherein the first and second restricted flow passages each is sized to accommodate the difference between leakage flow through the respective valve and the respective fluid motor. 17. A method as set forth in claim 13, wherein the first and second restricted flow passages are sized to provide a leakage flow of about 0.12 gallons per minute. 18. A method as set forth in claim 13, wherein the restricted flow passage includes an orifice and a filter upstream of the orifice to prevent clogging of the orifice. 19. A method as set forth in claim 13, wherein the first and second restricted flow passages include an orifice of no greater than about 0.020 inch in diameter, and wherein the first and second restricted flow passages are sized to provide a leakage flow of about 0.12 gallons per minute. 20. A method as set forth in claim 13, wherein the first and second restricted flow passages each is sized to accommodate the difference between leakage flow through the respective valve and the respective fluid motor, and wherein the first and second restricted flow passages are sized to provide a leakage flow of about 0.12 gallons per minute.