travel motor

Systems Operation 330D Excavator Hydraulic System

Travel Counterbalance Valve SMCS - 5051-KV

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Product: EXCAVATOR Model: 330D L EXCAVATOR B6H Configuration: 330D L Excavator B6H00001-UP (MACHINE) POWERED BY C9 Engine

Media Number -RENR9584-00 Publication Date -01/01/2006 Date Updated -01/02/2006

i02472619

Illustration 1 g00821157Left travel motor and travel counterbalance valve

(1) Crossover relief valve (reverse travel)

(16) Crossover relief valve (forward travel)

(24) Port (supply port for forward travel)

(27) Port (supply port for reverse travel)

(33) Counterbalance valve

(35) Travel counterbalance valve

Travel counterbalance valve (35) consists of counterbalance valve (33), crossover relief valve (1) and crossover relief valve (16). The travel counterbalance valve is bolted to the travel motor. The travel counterbalance valve has the following four functions.

The travel counterbalance valve prevents a shock load when travel is stopped.

The travel counterbalance valve prevents overspeed while the machine is travelling down a slope.

The travel counterbalance valve prevents cavitation.

The travel counterbalance valve routes a portion of the oil to the travel parking brake in order to release the brake.

Counterbalance Valve Operation During Level Travel

(36) Left travel motor

Illustration 2 g01233153

Travel counterbalance valve (level travel)


(2) Passage

(3) Valve

(4) Passage

(5) Passage

(6) Passage

(7) Passage

(8) Valve

(9) Spool

(10) Spring

(11) Passage

(12) Spring

(13) Spring

(14) Damper Spool

(15) Ball


(17) Passage

(18) Spring chamber

(19) Passage

(20) Damper Chamber

(21) Orifice

(22) Passage

(23) Check valve


(25) Passage

(26) Passage


Counterbalance valve (33) consists of spool (9), check valve (23), check valve (28), spring (13) and spring (30). During forward travel on level ground, pump oil is supplied to port (24). The oil flows through port (24), passage (25), and check valve (23). The oil flow forces check valve (23) to open. This allows oil to flow through port (24), passage (25), check valve (23), passage (2), and the port to the rotary group of the travel motor.

A portion of the oil delivery from the drive pump in port (24) flows through passage (22) and passage (17) against ball (15). Ball (15) moves to the right against the force of spring (12) in damper spool (14). The oil delivery then flows through passage (19) into spring chamber (18). The oil pressure in damper chamber (20) acts on the end of spool (9). Spool (9) shifts to the right against the force of spring (30). Passage (7) opens.

As spool (9) shifts to the right, return oil from the travel motor flows through the port, passage (7), passage (26), and port (27) to the hydraulic tank.

When the oil flow from port (24) is blocked, the pressure in damper chamber (20) decreases. The force of spring (30) shifts spool (9) to the left. Passage (7) closes. Return oil from the travel motor is blocked and the rotation of the travel motor stops.

When the direction of travel is reversed, pump oil flows to spool (9) through port (27). Spool (9) shifts to the left. The return oil flows through port (24). During reverse travel, the travel counterbalance valve operates in the same manner as the forward travel operation.

Counterbalance Valve Operation During Slope Travel

(28) Check valve

(29) Passage

(30) Spring

(32) Passage




Travel counterbalance valve (slope travel)


(2) Passage

(3) Valve

(4) Passage

(5) Passage

(6) Passage

(7) Passage

(8) Valve

(9) Spool

When the machine travels down a slope, the travel motors rotate at a higher speed. The higher speed is due to the mass (weight and size) of the machine. When this condition occurs, the pumps cannot maintain the oil supply to the travel motors. The lack of oil supply will cause cavitation in the travel motor. A pressure decrease occurs at port (24). A pressure decrease occurs in spring chamber (18) as well.

The force of spring (30) moves spool (9) to the left. Passage (7) begins to close. This blocks oil flow between passage (7) and passage (26). The return oil from the travel motor and the oil flow to the suction port of the travel motor are restricted. The rotation of the travel motor slows down.

(10) Spring

(11) Passage

(12) Spring

(13) Spring

(14) Damper Spool

(15) Ball


(17) Passage

(18) Spring chamber

(19) Passage

(20) Damper Chamber

(21) Orifice

(22) Passage

(23) Check valve


(25) Passage

(26) Passage


(28) Check valve

(29) Passage

(30) Spring

(32) Passage



The pressure of the oil delivery from the drive pump at port (24) increases. Part of the oil flows through passage (17). Spool (9) shifts to the right. Passage (7) opens. Return oil from the travel motor flows through port (27). The modulation of spool (9) maintains the proper opening of passage (7) when the machine travels down a slope. The travel motor begins to rotate in accordance with the amount of pump oil supply. This prevents cavitation in the travel motors.

When the machine is travelling down a slope, or the machine is suddenly stopped, spool (9) suddenly closes passage (7). This causes a hydraulic pressure spike to occur. A damper is provided at both ends of spool (9) in order to prevent hydraulic pressure spikes. As spool (9) shifts to the left, the oil in damper chamber (20) is pressurized. Ball (15) moves to the left. The oil in spring chamber (18) flows through orifice (21) and into passage (22). Spool (9) slowly moves to the left. Passage (7) slowly closes. The size and the position of orifice (21) maintains the proper shock damper.

Operation Of Travel Crossover Relief Valves During Machine Stop


Travel counterbalance valve (travel stop)


(2) Passage

(3) Valve

(4) Passage

(5) Passage

(6) Passage

(7) Passage

(8) Valve

(9) Spool

(10) Spring

(11) Passage

(12) Spring

(13) Spring

(14) Damper Spool

(15) Ball


(17) Passage

(18) Spring chamber

(19) Passage

(20) Damper Chamber

(21) Orifice

(22) Passage

(23) Check valve


(25) Passage

(26) Passage


(28) Check valve

If the travel levers/pedals are returned to the NEUTRAL position during machine movement, the oil delivery from the pumps is blocked from the travel motors. The pressure at port (24) of the travel counterbalance valve decreases. The force of spring (30) moves spool (9) to the left to the neutral position. The mass (weight and size) of the machine causes the travel motor to continue to rotate. Passage (7) is closed and the flow of return oil is blocked. A sudden pressure increase occurs in passage (11). The return oil in passage (11) flows through passage (6) to crossover relief valve (1). Valve (3) shifts to the left. The return oil in passage (6) flows past the open valve (3) into suction passage (2) of the travel motor.

(29) Passage

(30) Spring

(32) Passage




Travel crossover relief valve

(3) Valve

(2) Passage

(6) Passage

(39) Body

(40) Orifice

(41) Orifice

(42) Orifice

The return oil pressure in passage (6) flows through orifice (41) in valve (3). The oil then flows through orifices (40) and (42) in stem (43). The return oil now flows through passage (44). Shock reducing piston (45) shifts to the right. The travel crossover relief valve maintains the circuit pressure at a lower pressure until the right end of shock reducing piston (45) contacts stem (43). When the shock reducing piston is fully shifted to the right, the oil pressure in passage (6) increases to the pressure setting of the crossover relief valve. All of the oil flow in passage (6) now flows past valve (3) into return passage (2) .

The oil pressure gradually increases until the shock reducing piston shifts fully to the right. Pressure spikes in the travel circuit are eliminated. This is called a two-stage relief operation. The two-stage relief operation absorbs the shock load at the stop of a travel operation.

During forward travel of the left travel motor, oil flow opens crossover relief valve (1) when the machine is stopping. During reverse travel of the left travel motor, crossover relief valve (16) is activated when the machine is stopping.

Crossover relief valves (1) and (16) protect the travel motor by releasing the high pressure oil.

Crossover relief valves (1) and (16) also provide makeup oil from the outlet side of the travel motor to the inlet side of the travel motor. This makeup oil prevents a vacuum condition in the travel motor.

In order to adjust the pressure setting of the crossover relief valves, refer to the crossover relief valves by the functions of the travel control levers. Refer to crossover relief valve (16) as left travel (forward). Refer to crossover relief valve (1) as left travel (reverse).

ReferenceFor more information concerning the pressure settings of the travel crossover relief valves, refer to Testing and Adjusting, "Relief Valve (Crossover) - Test and Adjust".

Travel Parking Brake Operation When the oil delivery from the drive pump at port (24) of the travel counterbalance valve is blocked, spool (9) moves to the right. Passage (4) opens. A portion of the oil delivery in passage (25) flows through passage (4) and passage (32) in order to release the travel parking brake. Since passage (4) opens before passage (7), the rotation of the motor rotary group does not start until the travel parking brake is released.

When the oil delivery to port (24) is blocked in order to stop the rotation of the travel motor, spool (9) returns to the NEUTRAL position. Passage (4) closes after passage (7) closes. This allows the movement of the machine to stop before the travel parking brake is engaged.

ReferenceFor more information concerning the operation of the travel parking brake, refer toSystems Operation, "Travel Parking Brake".

(43) Stem

(44) Passage

(45) Shock reducing piston

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Wed Feb 28 19:53:48 EST 2007

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