Apparatus for controlling work element operating pressures in a fluid system

Claim 2

In a fluid system having a pressurized fluid source connected to at least one working element through a safety pressure relief valve constructed to open in response to a first preselected pressure, and a control valve assembly having a flow control valve positioned between a directional control valve and the pressurized fluid source, said directional control valve having a first conduit connected to one end of the work element for controllably passing fluid therebetween, the improvement comprising: signal means in fluid communication with the first conduit for sensing the fluid pressure in said conduit and delivering said sensed pressure as a pressure signal to the flow control valve for controllably biasing said flow control valve toward an open position in response to said delivered pressure signal; and a signal pressure relief valve connected in fluid communication with the signal means for controllably passing fluid from the signal means for limiting the pressure on the working element to a second preselected value, said second preselected value being less than said first preselected value of said safety pressure relief valve.

Claim 3

Apparatus, as set forth in claim 1, wherein the pressurized fluid source is connected to a plurality of working elements through the safety pressure relief valve, each working element being connected to a separate control valve assembly having a respective flow control valve positioned between a respective directional control valve and the pressurized fluid source, each directional control valve having a first conduit connected to a respective work element for controllably passing fluid therebetween, and including: separate signal means each being in fluid communication with a respective first conduit for sensing the fluid pressure in said conduit and delivering said sensed pressure as a separate pressure signal to a respective flow control valve for controllably biasing said flow control valves toward open positions in response to said delivered pressure signals; and separate signal pressure relief valve each being connected in fluid communication with a respective signal means for controllably, separately passing fluid from the signal pressure relief valve for maintaining the pressures on said respective working elements at preselected values.

Claim 4

Apparatus, as set forth in claim 2, wherein the plurality of signal pressure relief valves each have a preselected pressure, said preselected pressures of the plurality of signal pressure relief valves are each of a lower magnitude than the first preselected pressure of the safety pressure relief valve, and at least one of the signal pressure relief valves has a preselected pressure of a different magnitude than other relief valve preselected pressures.

Claim 5

Apparatus, as set forth in claim 1, including: a second conduit connected to another end of the work element and to the directional control valve for controllably passing fluid therebetween; and wherein the signal means is in fluid communication with the second conduit and is of a construction for delivering the larger of the sensed pressures of the first and second conduits as said pressure signal.

Claim 6

Apparatus, as set forth in claim 1, wherein said flow control valve is a two-way valve movable between a first position at which flow is blocked between the pressurized fluid source and the directional control valve and a second position at which the pressurized fluid source and the directional control valve are in fluid communication.