Efficiency Check For The Travel Make-Up Flow During Travel Operation Caterpillar

Efficiency Check For The Travel Make-Up Flow During Travel Operation

Usage:

EXCAVATORSM312 (6TL),
M315 (7ML),
M318 (8AL, 6ES, 8SS),
M320 (6WL, 9PS) EXCAVATORS

Problem:

Hydraulic system debris resulting from travel motor and/or travel line relief valve failures can cause travel circuit check valves to not operate properly. Travel circuit check valve failures will decrease the make-up flow to the travel motor and shorten the service life of its components.

Solution:

If a travel motor and/or travel line relief valve fails you must check the make-up flow to the travel motor after the repair process is completed. Use the following procedure to check the make-up flow.

Procedure to check the make-up flow to the travel motor:

1. Perform the 145-6192 Relief Valve Group Product Improvement Program (Pi3035) procedure (if it applies to your model and PIN) prior to beginning the make-up flow check. Proceed to step 2 if this procedure has been completed.

2. Add a tee connector and a pressure gauge at the Tank Port of the main control valve (Illustration 1).

a. The pressure gauge should always read a minimum of 5 bar (72 psi). The 5 bar (72 psi) minimum must be maintained over the full rpm range of the excavator and during travel. The excavator must also maintain the 5 bar (72 psi) minimum while the engine is running and the machine is not traveling.

b. The pressure gauge should read a minimum of 5 bar (72 psi), when the machine is traveling full speed down a grade and the travel pedal is released suddenly.

Illustration 1.

(1) Add tee and p ressure gauge.

Travel make-up flow diagnosis and repair: (if the travel motor make-up flow is below the minimum of 5 bar (72 psi))

1. If the machine will travel in only one direction, the make-up oil is most likely being diverted through an open make-up valve inside the 121-9948 Travel Motor Brake Valve (Illustration 2).

Repair procedure:

Remove the brake valve.

Clean the suspect make-up valves.

Assemble the brake valve and reinstall it.

Illustration 2.

Travel motor brake valve.

(2) Suspect make-up valves.

2. If the machine travels normally but the travel make-up flow is below the minimum 5 bar (72 psi). The 8U-7566 Make-up Valve located in the oil return manifold (Illustration 3) is likely to be open.

Repair procedure:

Remove the 8U-7566 Valve.

Clean the valve and its seat and reinstall the valve.

Illustration 3.

Return oil manifold located at the hydraulic tank.

(3). 8U-7566 Make-up Valve.

3. If the make-up flow is below specifications after the two previous checks, the pilot flow must be checked at port T1/T2 of the pilot manifold (Illustration 6).

Specifications:

Machines equipped with a 19 ccm pilot pump (Illustration 4), should read 19 l/min, at T1/T2 when the engine runs at 1000 rpm.

Machines equipped with a 26 ccm pilot pump (Illustration 5), should read 26 l/min, at T1/T2 when the engine runs at 1000 rpm.

If the pilot pump flow is not within specifications, check the pilot pump and its drive.

Illustration 4.

19 ccm pilot pump (4). External diverter block for the steering pump.

Illustration 5.

26 ccm pilot pump (5). Integrated diverter valve for the steering pump.

Illustration 6.

Hydraulic travel circuit schematic.

NOTE: Illustration 6 is an overview of the hydraulic travel operation components. Use this schematic to troubleshoot the hydraulic travel circuit.