Usage:
All Caterpillar Products With Axial Piston Pumps
Whenever you rebuild or replace parts of the rotating group (barrel assembly and pistons) of a piston pump, you should follow the correct priming and break-in procedure. This is very important since failures in rebuilt piston pumps not properly primed/broken-in have been known to occur at relatively low hours of operation, leaving little or no evidence as to the cause of failure.
A typical failure of this nature usually results in total destruction of the lower end of the pump. More specifically, slippers are pulled from the pistons, the retraction plate breaks into numerous pieces and the retraction bearing and retaining bolts are destroyed. If the pistons can be removed from the barrel assembly, you may find elongated shiny areas on the inside diameter of the sleeves. This usually indicates a piston seized sometime during initial start-up. Piston seizure may have caused the retraction plate to bend upward in the middle (become convex), or slippers to become loose on the pistons and/or retraction bearing retaining bolts to become loosened by elongation.
Break-in of a rebuilt pump and/or hydrostatic transmission should be conducted according to the procedure in "Bench Testing of Hydraulic Components," Form No. SEHS7972. However, if the use of a hydraulic test bench is not practical, use one of the following procedures.
Pump Break-In For Hydraulic Excavators And Wheel Loaders
1. After installing the pump on the machine, fill the pump housing with oil through the case drain port.
2. Loosen the discharge line on the pump and the fill cap on the hydraulic tank. (Be sure the oil level is correct.)
3. With the throttle in the OFF position, prime the pump by turning the engine with the starter until oil seeps from the discharge connection at the pump.
4. Tighten the discharge line and fill cap. (Once again, be sure the oil level is correct.)
5. Start the engine and let it run at low idle. Operate the hydraulic circuits until the system reaches operating temperature (about 15 minutes).
| NOTICE |
|---|
Do not operate the hydraulic system at relief pressures before the system reaches operating temperature.
|
6. Increase engine speed to approximately 1500 rpm. Operate the hydraulic circuits at relief pressures for a maximum of 8 seconds, wait a minimum of 30 seconds and repeat. Repeat this procedure 8 to 10 times.
7. Increase engine speed to high idle and repeat the 8 seconds "on," 30 seconds "off" operation just described.
| NOTICE |
|---|
Do not allow hydraulic oil temperature to rise above 80°C (180°F) at any time during the break-in procedure.
|
8. Return controls to their HOLD position and run the engine at high idle for a minimum of 5 minutes.
Pump Break-In For Motor Graders
1. After installing the pump on the machine, fill the pump housing with oil through the case drain port.
2. Loosen the discharge line and the fill cap on the hydraulic tank. (Be sure the oil level is correct.)
3. With the throttle in the OFF position, prime the pump by turning the engine with the starter until oil seeps from the discharge connection at the pump.
4. Tighten the discharge line and fill cap. (Once again, be sure the oil level is correct.)
5. Disengage the unloader valve and start the engine. Run at low idle until the oil system temperature is about 52°C (125°F).
6. With the engine still at low idle, carefully release the unloader valve and operate the blade up and down. Take care not to reach the end of the cylinder travel. Do this for about 10 minutes.
7. Increase engine speed to approximately 1500 rpm and operate the circle drive back and forth for approximately 15 minutes.
8. On 130G, 140G, 12G, 14G and 16G Motor Graders, check pumps for staging. Pumps should downstage to the standby pressure of 14 800 kPa (2150 psi) from the second stage pressure of 24 100 kPa (3500 psi) in 5 to 10 seconds. Failure of the pump to stage correctly could be the result of a leaking ball check in the main control valve, excessive case drainage, a faulty servo or pressure reducing valve, a leaking/sticking shuttle valve, an improperly adjusted main relief, or leakage at the unloader valve.
Break-In Procedure For Hydrostatic Transmissions
1. After installing the unit on the machine, prime the pumps by filling the transmission case to the FULL mark on 963 and 973 Loaders and to 220 mm (8.7") above the FULL mark on 943 and 953 Loaders. Fill the transmission filter housing.
2. With the throttle in the OFF position, turn the transmission with the engine starter for three 5-second intervals.
3. Start the engine twice at low idle, each time, stopping when the charge pressure reaches 400 kPa (58 psi).
4. Drain the transmission case on 943 and 953 Loaders only until the oil level is 100 mm (4.0") above the FULL mark.
5. If the unit has not been tested on a hydraulic test bench as outlined in "Bench Testing Hydraulic Components," Form No. SEHS7927, use the following break-in procedure:
a. After completing steps 1, 2, 3 and 4, put the U-tube in the test position.
b. Start the engine and run it at low idle for about 5 minutes.
c. Increase engine speed to 1000 rpm. Occasionally pull transmission speed control toward forward, then toward reverse speed to obtain 10 300 kPa (1500 psi). Do this for about 5 minutes.
d. Increase engine speed to 1500 rpm. Occasionally pull transmission speed control toward forward, then toward reverse speed to obtain 37 900 kPa (5500 psi). Do this for about 5 minutes.
e. Increase engine speed to high idle. Occasionally pull the transmission speed control toward forward, then toward reverse to obtain 37 900 kPa (5500 psi). Do this for about 5 minutes.
6. Stop the engine and adjust the transmission case oil level to the FULL mark.
NOTE: This article was also printed in "Analyzing Axial Piston Pump And Motor Failures," Form SEBD0641.