To provide a piping rupture control device capable of achieving the control for moderating the load descending speed by the small flow rate control, mounting the same pilot spool in different hydraulic work machines, shortening the total length of the pilot spool, and facilitating the manufacture of a diaphragm.
The device comprises a cylinder port 19 continuous to a boom cylinder 6, a control valve port 20 continuous to a direction control valve 10, the pilot spool 22 for controlling a poppet 21, and an oil pathway 28 with the diaphragm function for making the cylinder port 19 and a back pressure chamber 29 communicate with each other. The pilot spool 22 has a variable diaphragm for making the back pressure chamber 29 and the direction control valve 10 communicate with each other, and also has signal pathways 32 and 33 formed in a housing 18 located outside the poppet 21 for making the cylinder port 19 and the back pressure chamber 29 of the poppet 21 communicate with each other and a fixed diaphragm 34 disposed in the signal pathway 33.
NOZAWA YUSAKU
ITO HIDEAKI
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