selbsttaetig operating valve device for the controlled causing prestressed ruecklauf fluid in the line between two series-connected pumps, in particular for the hydraulic line system of agricultural tractors

摘要

A hydraulic system having a reservoir fed charge pump supplying pressurized fluid through a charge passage and a filter to the inlet of a supply pump for direction controlled fluid devices includes a reservoir connected unloading valve assembly connected to the charge passage and parallel with the filter. The fluid devices return fluid through a return passage connected to the unloading valve assembly which maintains back pressure on the devices at charge passage pressure. The unloading valve assembly includes an unloading valve movable in response to a predetermined fluid pressure at the inlet of the supply pump to unload the charge and return passage by connecting them to the reservoir. As the devices require more fluid from the supply pump causing the pressure at the inlet of the supply pump to drop, the unloading valve proportionately blocks the charge and return passages from the reservoir to circulate return fluid into the charge passage. The unloading valve assembly further includes a signal valve which responds to a predetermined pressure differential across the filter to provide a signal indicative of a clogged filter and to cause the unloading valve to connect both the charge and return passages to the reservoir in such a situation.