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Kubota BX1850, BX1860, BX1870 - LA203 Front End Loader

Kubota LA203 Front End Loader - Hydraulic Operations

UP position

1 - Boom Control Section, 2 - Bucket Control Section, 3 - Spool, 4 - P.B. Passage 1, 5 - Neutral Passage 1, 6 - Load Check Valve, 7 - Passage 1, 8 - Boom Cylinder, P - P Port (From Pump), T - T Port (To Tank), A1 - A1 Port (From Boom Cylinder), B1 - B1 Port (To Boom Cylinder), P.B - P.B. Port (To 3 Hitch), a - Low Pressure, b - High Pressure

When the hydraulic control lever is set to the “UP” position, the spool (3) of the boom control section (1) moves to the left, which forms oil passages between passage 1 (7) and B1 port, and between A1 port and P.B. passage 1 (4). As the oil passage from the neutral passage 1 (5) to the P.B. passage 1 (4) is closed by the spool (3), the pressure fed oil from the P port opens the load check valve (6) and flows through the notched section of the spool (3) and B1 port to extend the boom cylinder (8). Return oil from the boom cylinder (8) flows from the A1 port through the passage in the spool (3) and P.B. passage 1 (4) to the bucket control section (3).

DOWN position

1 - Boom Control Section, 2 - Bucket Control Section, 3 - Spool, 4 - P.B. Passage 1, 5 - Neutral Passage 1, 6 - Load Check Valve, 7 - Passage 1, 8 - Boom Cylinder, P - P Port (From Pump), T - T Port (To Tank), A1 - A1 Port (From Boom Cylinder), B1 - B1 Port (To Boom Cylinder), P.B - P.B. Port (To 3 Hitch), a - Low Pressure, b - High Pressure

When the hydraulic control lever is set to the “DOWN” position, the spool (3) moves to the right, which forms oil passages between passage 1 (7) and A1 port, and between B1 port and P.B. passage 1 (4). As the oil passage from the neutral passage 1 (5) to the P.B. passage 1 (4) is closed by the spool (3), the pressure fed oil from the P port opens the load check valve (6) and flows through the notched section of the spool (3) and A1 port to retract the boom cylinder (8). Return oil from the boom cylinder (8) flows from the B1 port through the passage in the spool (3) and P.B. passage 1 (4) to the bucket control section (2).

FLOAT position

1 - Boom Control Section, 2 - Bucket Control Section, 3 - Spool, 4 - P.B. Passage 1, 5 - Detent Mechanism, 6 - Neutral Passage 1, 7 - Boom Cylinder, P - P Port (From Pump), T - T Port (To Tank), A1 - A1 Port, B1 - B1 Port, P.B - P.B. Port (To 3 Hitch), a - Low Pressure

When the hydraulic control lever is set to the “FLOAT” position, the spool (3) moves further to the right from the “DOWN” position and is retained by the detent mechanism (5). This forms oil passages among the A1 port, B1 port and T port. As a result, oil in the boom cylinder (7) flows freely from the A1 port and B1 port through the T port to the transmission case. Oil entering the P port flows to the bucket control section (2) through the neutral passage 1 (6) and P.B. passage 1 (4).

Kubota LA203 Loader - ROLL-BACK position

1 - Boom Control Section, 2 - Bucket Control Section, 3 - P.B. Passage 1, 4 - Spool, 5 - Neutral Passage 2, 6 - P.B. Passage 2, 7 - Load Check Valve, 8 - Passage 2, 9 - Bucket Cylinder, P - P Port (From Pump), T - T Port (To Tank), P.B - P.B. Port (To 3 Hitch), A2 - A2 Port (From Bucket Cylinder), B2 - B2 Port (To Bucket Cylinder), a - Low Pressure, b - High Pressure

When the hydraulic control lever is set to the “ROLL-BACK” position, the spool (4) of the bucket control section (2) moves to the left, which forms oil passages between passage 2 (8) and B2 port, and between A2 port and T port. The pressure-fed oil from the P port flows to the neutral passage 2 (5) through the boom control section (1) and P.B. passage 1 (3). As the oil passage from the neutral passage 2 (5) to the P.B. passage 2 (6) is closed by the spool (4), this oil opens the load check valve (7), and flows through the notched section of the spool (4) and B2 port to retract the bucket cylinder (9). Return oil from the bucket cylinder (9) flows to the transmission case through the A2 port and T port.

DUMP 1 position

1 - Boom Control Section, 2 - Bucket Control Section, 3 - P.B. Passage 1, 4 - Spool, 5 - Neutral Passage 2, 6 - P.B. Passage 2, 7 - Load Check Valve, 8 - Passage 2, 9 - Bucket Cylinder, P - P Port (From Pump), T - T Port (To Tank), P.B - P.B. Port (To 3 Hitch), A2 - A2 Port (From Bucket Cylinder), B2 - B2 Port (To Bucket Cylinder), b - High Pressure

When the hydraulic control lever is set to the “DUMP 1” position, the spool (4), which forms oil passages among passage 2 (8), A2 port and B2 port. The pressure-fed oil from the P port flows through the boom control valve, opens the load check valve, and flows to the bucket cylinder to extend the cylinder through the notched section of the spool and A2 port. Return oil from the bucket cylinder (9) flows from the B2 port to the passage 2 (8), and flows to the A2 port together with the pressure-fed oil from the P port. As a result, the dump speed is increased. The oil pressure of the A2 port and B2 port is identical, but the bucket cylinder extends by the difference of received pressure area (cylinder rod part).

DUMP 2 position

1 - Boom Control Section, 2 - Bucket Control Section, 3 - P.B. Passage 1, 4 - Spool, 5 - Neutral Passage 2, 6 - P.B. Passage 2, 7 - Load Check Valve, 8 - Passage 2, 9 - Bucket Cylinder, P - P Port (From Pump), T - T Port (To Tank), P.B - P.B. Port (To 3 Hitch), A2 - A2 Port (From Bucket Cylinder), B2 - B2 Port (To Bucket Cylinder), a - Low Pressure, b - High Pressure

When the hydraulic control lever is set to the “DUMP 2” position, the spool (4) of the bucket control section (2) moves to the right of the bucket control section (2) moves further to the right from the “DUMP 1” position, which forms oil passages between passage 2 (8) and A2 port, and between B2 port and T port. The pressure-fed oil from the P port flows to the neutral passage 2 (5) through the boom control section (1) and P.B. passage 1 (3). As the oil passage from the neutral passage 2 (5) to the P.B. passage 2 (6) is closed by the spool (4), this oil opens the load check valve (7) and flows through the notched section of the spool (4) and B2 port to extend the bucket cylinder (9). Return oil from the bucket cylinder (9) flows to the transmission case through the B2 port and T port.

Kubota BX1850, BX1860, BX1870 - Boom Cylinder And Bucket Cylinder

1 - Nut, 2 - Piston, 3 - Cylinder Tube, 4 - Head, 5 - Piston Rod

Both boom cylinder and bucket cylinder consists of a head (4), cylinder tube (3), piston rod (5), piston (2), and other parts as shown in the figure above. They are single-rod double acting cylinder in which the reciprocating motion of the piston is controlled by hydraulic force applied to both of its ends.

Kubota BX1850, BX1860, BX1870 - Control Valve

1-Pipe, 2-Cruise Control Rod, 3-Front Loader Control Rod, 4-Arm, 5-Stay, 6-Loader Frame, 7-Valve Stay, 8-Control Valve, 9-Propeller Shaft, 10-Front Loader Control Lever, 11-Rod 1, 12-Rod 2, 13-Rod 3

Remove the loader frame (6). Disconnect the cruise control rod (2). Disconnect the frame loader control rods (3). Remove the brake spring. Remove the arms (4) from spool end. Remove the stay bolt (5). Remove the valve stay (7). Disconnect the pipes (1). Remove the control valve (8) with pipes. After reassembling a valve, check for oil leakage by starting up engine. When starting up engine, watch out for the rotating propeller shaft (9). When adjusting the length of rods, make the lever come to the neutral position. A = 145 mm (5.71 in.), B = 315 mm (12.4 in.), C = 448 mm (17.6 in.).

How to mount LA203 front end loader on Kubota BX1850, BX1860, BX1870 tractor

Side Frame and Hoses

1-Side Frame, 2-Main Frame, 3-Hose, 4-Loader Control Lever, 5-Spring Pin, 6-Stand

Slowly drive a Kubota BX1850, BX1860, BX1870 tractor between the loader side frames until the rear portion of both side frames touches the main frames. Stop the engine. Connect four hoses with couplers to the nipple on the control valve as indicated with color marks. Then connect the protective caps and plugs to each other. Start the engine and run at idle. Slowly move the loader control lever to dump position to lower the side frames into the main frames and engage the bosses of the main frames to the guide bosses of the side frames. Then lift the front wheels slightly with a Kubota LA203 loader. Do not attempt to lift the front wheels with the stand. Stop the engine. Reinstall the mounting pins and secure them with the locking rods. Start the engine. Raise the boom until the stand can be rotated. Stop the engine. Store the stand to their original positions and secure it with the spring pin. Start the engine. Lower the boom and level the bucket.

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