Troubleshooting Propel Surge Caterpillar

Troubleshooting Propel Surge

Usage:

VIBRATORY SOIL COMPACTORCB-434C (4DN1-UP)

Problem:

Certain CB-434C Asphalt Compactors have experienced surging of the Propel System. The surging may occur and be most noticeable when initiating machine movement, or when propelling on positive, negative, or zero grades. Propel run-on or coasting at low speeds is another propel problem that has been noted. The propel run-on problem may be caused by cross-port seal leakage in the propel motor. Bad distributor valve seals can allow cross-port leakage, that will not cause increased case flow. If no solution is found through normal troubleshooting procedures, the following checks are recommended to evaluate the motor:

Solution:

As a preliminary check remove and check the high pressure relief valves. Make sure the springs are in the correct position. Physically check inside the pump to make sure the springs were not installed under the relief valve and remain stuck in the relief valve bores.

The propel circuit uses parallel flow with no flow divider, so a problem in either motor will result in the same symptoms. Both motors may need to be tested.

As part of the SOLUTION, perform the following test procedures for FOUR identified surge conditions:

1. SURGE WHEN INITIATING PROPEL: Install a high pressure flow meter to the return loop line of one of the motors. Operate the machine in a manner that will duplicate the surge condition. Duplicating the problem is necessary to accurately troubleshoot the machine. Slightly move the propel lever, but keep it at a point where the machine will not move. This is the point at which the flow meter must be observed. If the flow meter shows that flow is present in the return loop and the machine has not yet begun to move, it is an indication that a problem exists with the seals around the distributor valve of the motor.

2. SURGE WHEN PROPELLING ON FLAT OR UPHILL CONDITIONS: Install a high pressure flow meter to the return loop line of one of the motors. Install pressure gauges to read pressures on both the pressure and the return loops. Operate the machine to duplicate the surge condition while observing the flow meter and gauge in the high pressure side of the loop. A seal problem in this condition will be indicated by a near constant flow, with pressure fluctuations in the high pressure loop. The pressure will drop to approximately charge pressure when the machine coasts. It will then spike on the upstream or pressure side of the motor when the machine surges forward.

3. SURGE WHEN PROPELLING DOWNHILL: Install a high pressure flow meter to the return loop line of one of the motors. Install pressure gauges to read pressures to read on both the pressure and return line of the motor. Operate the machine to duplicate the surge condition while observing the flow meter and gauge in the return side of the loop. A seal problem in this condition will be indicated by a near constant flow, with pressure spikes in the return side of the loop when a breaking surge occurs. The return pressure may drop to charge pressure in a coast condition and spike as the seal reseats and allows hydrostatic braking to occur.

4. PROPEL RUN-ON AFTER THE CONTROL LEVER IS RETURNED TO NEUTRAL: Install pressure gauges and flow meter as described above. Operate the machine to duplicate the run-on condition while observing the flow meter and gauges in both sides of the loop. A seal problem in this condition will be indicated by continued machine run-on with zero flow and pressure gauges reading charge pressure on both sides of the loop.

NOTE: If the condition is duplicated and no flow/pressure problems are found in the motor being tested, check the remaining motor using the same procedures.

NOTE: If the valve seals are determined to be at fault, contact Caterpillar Paving Products to report seal problems and to get additional information before making repairs.