COMPONENT OPERATION ／ HST Pump ・Inching valve assembly（YUKEN ／ Serial No. 1001 〜 4499） 1.The oil from the charging pump enters from port A and divides into two, going to the orifice ④ of the pressure control valve spool ① and the orifice of the valve body ② . 2.When the oil sent to the pressure control valve spool ① passes through the orifice ④ a different pressure is created before and after the orifice because the different pressure moves the spool ① to the spring ③ side against the spring force. 3.The valve body ② functions as the variable orifice. When the variable orifice ⑩ is closed, all the oil goes from the charging pump to the pressure control valve spool ① . When the variable orifice ⑩ is fully opened, all the oil goes from charging pump to port B through the valve Body ② . In this case, pilot pressure is not created. his function is connected with brake pedal of the machine, and is using as the inching control. 4.The oil from port B joins the oil from port D through the relief valve ⑧ and returns to the oil tank through the pump drain port. 5.The pilot pressure ( ΔPc) is led to port C to control the pump discharge quantity. The pilot pressure from port C goes to the piston chamber which controls the pump discharge, through the electromagnetic selector valve. 6.The pump speed changes the proportionally charging pump's discharge so that the engine speed is sensed after it has been converted to the charging pump's discharge.
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