Abstract: A hydraulic relief valve has a spring to offset an acting force of a spring resiliently supporting a main poppet so as to improve the make-up function of supplementing a hydraulic fluid since the outflow rate is higher than the inflow rate when the cylinder is retracted by an external force, in the case in which a pilot piston type of relief valve having a pilot piston displaceable in an orifice penetrating a main poppet is applied to a hydraulic system equipped with a cylinder. The pilot piston is provided with a circular rib on an external surface thereof, and an external surface of the orifice is partially cut to form a space around the external surface of the pilot piston. The external spring is installed between the valve seat and the external surface of the rib, and the internal spring is installed between the internal surface of the rib and the cut surface of the main poppet.

Abstract: A pressure compensating flow control hydraulic circuit having a holding valve is disclosed. The pressure compensating flow control hydraulic circuit can perform the function of a holding valve so as to prevent the naturally lowering phenomenon of a working unit due to the leakage of a hydraulic fluid when the working unit is located in a neutral position, and can perform the function of a flow control valve when the working unit is operated.

Abstract: Disclosed is a flow control apparatus for construction heavy equipment capable of maintaining constant set flow rate regardless of changes in load pressure and pump pressure. The flow control apparatus is composed of a control valve, a flow control valve, and a load check valve. The control valve has a parallel passage, a housing provided with a first load passage and a second load passage, and a control spool provided to be movable in the housing. The flow control valve having a logic check valve provided to be openable between the first load passage and the parallel passage, and a logic control valve controlling a flow rate supplied to a back pressure chamber of the logic check valve. The load check valve is provided between the second load passage and the parallel passage to restrict backflow from the second hydraulic cylinder.

Abstract: Disclosed is a relief valve, in which a flow rate of hydraulic fluid is not greatly changed even when temperature is changed, and thus providing smooth operation and preventing foreign materials contained in the hydraulic fluid from being introduced into the relief valve. The relief valve is comprised of a sleeve provided with a high-pressure inlet and a tank fluid channel; a main poppet provided with an inflow fluid passage and a back pressure chamber; an annular fluid passage provided on a front end of the main poppet; a seat provided with a seat fluid channel communicating with the back pressure chamber; and a pilot poppet communicating the seat fluid channel with the tank fluid channel.

Abstract: A relief valve, filtering foreign materials contained in hydraulic fluid, is comprised of a sleeve provided with a high-pressure inlet and a tank fluid channel; a main poppet provided with a back-pressure chamber and fitted in the sleeve so as to open/close the high-pressure inlet and the tank fluid channel; a piston provided with a piston fluid passage communicating the high-pressure inlet with the back-pressure chamber; an annular fluid passage defined by an inner wall of the poppet passage of the main poppet and an outer wall of the piston and communicating with the piston fluid passage; a seat fitted in a rear of the main poppet to support a rear end of the main poppet spring and provided with a seat fluid channel; and a pilot poppet fitted to open/close the seat fluid channel, and communicating the seat fluid channel with the tank fluid channel.

Abstract: The present invention discloses a structure for mounting a coin-filter filtering foreign materials contained in hydraulic fluid on a fixing groove formed at an inlet side of an orifice without using O-ring. A coin-filter mounting structure according to the present invention comprises a body having a fixing groove formed at an inlet side of an orifice, and a holder supporting the border of a coin-filter filtering out foreign materials contained in hydraulic fluid flowing through the orifice, and fixed to the fixing groove through plastic deformation after being mounted on the fixing groove.