I have a hitachi zx50u-2 that is bogging down under load and will sometimes stall. When crawling the motor will loose rpms and same with digging. I have replaced fuel filter and new electric fuel pump. Filled with new hyd oil. The machine sat for 8 years but was running great when parked. The motor was hydrolocked and had to be rebuilt. Pilot pressure is good but not very inclined on checking relief valves or anything else. Manual says to check revolution sensing valve but I'm not real sure what to do other than visually inspecting the valves
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Hitachi zx50u-2 bogging under load, has no digging power
- Thread starter davidc721
- Start date
Checking the Revolution sensing valve means testing the output pressure from the Revolution sensing valve and it is done as follows.
1. Connect a T with a pressure test point to the hose between the Revolution sensing valve and the PS valve on the main hydraulic pump.
2. Warmup the hydraulic oil to 122 degree F.
3. Check and if necessary adjust the pilot pressure. Correct value is 960psi at fast idle.
4. Check the output pressure of the Revolution sensing valve (pressure PGR) at slow idle (1150 rpm). Correct value is 71 psi.
5. Check pressure PGR at fast idle (2650 rpm). Correct value is 285 psi.
If the pressure PGR is too low the hydraulic power will be too low.
If the pressure PGR is too high the load on the engine will be too high (but not overloaded) at light duty operations but not at heavy duty operations.
Don t adjust the pressure PGR unless you really understand how to do it.
The pressure PGR and the pressure PLS from the pressure differencial valve in the main control valve balances against each other in the PS valve on the hydraulic pump to make the machine smooth and fuel efficient and not to control max power. Max power control is done internally in the hydraulic pump with a spring whitch balances the swashplate against the pressure from the plungers in the pump. The power control is adjusted by the allen bolt above the pilot pump and I would start by adjusting it out 1 full turn at the time. If the engine still is overloaded after 4-6 turns I would suspect the hydraulic pump. If the engine load decreases and the machine is slow after 4-6 turns the engine lacks power. Make notes of how much you adjust the pump to be able to reset it.
If the machine has aircondition i suggest you check the function of the torque control solenoid valve.
1. Connect a T with a pressure test point to the hose between the Revolution sensing valve and the PS valve on the main hydraulic pump.
2. Warmup the hydraulic oil to 122 degree F.
3. Check and if necessary adjust the pilot pressure. Correct value is 960psi at fast idle.
4. Check the output pressure of the Revolution sensing valve (pressure PGR) at slow idle (1150 rpm). Correct value is 71 psi.
5. Check pressure PGR at fast idle (2650 rpm). Correct value is 285 psi.
If the pressure PGR is too low the hydraulic power will be too low.
If the pressure PGR is too high the load on the engine will be too high (but not overloaded) at light duty operations but not at heavy duty operations.
Don t adjust the pressure PGR unless you really understand how to do it.
The pressure PGR and the pressure PLS from the pressure differencial valve in the main control valve balances against each other in the PS valve on the hydraulic pump to make the machine smooth and fuel efficient and not to control max power. Max power control is done internally in the hydraulic pump with a spring whitch balances the swashplate against the pressure from the plungers in the pump. The power control is adjusted by the allen bolt above the pilot pump and I would start by adjusting it out 1 full turn at the time. If the engine still is overloaded after 4-6 turns I would suspect the hydraulic pump. If the engine load decreases and the machine is slow after 4-6 turns the engine lacks power. Make notes of how much you adjust the pump to be able to reset it.
If the machine has aircondition i suggest you check the function of the torque control solenoid valve.
Hi Kjell,Checking the Revolution sensing valve means testing the output pressure from the Revolution sensing valve and it is done as follows.
1. Connect a T with a pressure test point to the hose between the Revolution sensing valve and the PS valve on the main hydraulic pump.
2. Warmup the hydraulic oil to 122 degree F.
3. Check and if necessary adjust the pilot pressure. Correct value is 960psi at fast idle.
4. Check the output pressure of the Revolution sensing valve (pressure PGR) at slow idle (1150 rpm). Correct value is 71 psi.
5. Check pressure PGR at fast idle (2650 rpm). Correct value is 285 psi.
If the pressure PGR is too low the hydraulic power will be too low.
If the pressure PGR is too high the load on the engine will be too high (but not overloaded) at light duty operations but not at heavy duty operations.
Don t adjust the pressure PGR unless you really understand how to do it.
The pressure PGR and the pressure PLS from the pressure differencial valve in the main control valve balances against each other in the PS valve on the hydraulic pump to make the machine smooth and fuel efficient and not to control max power. Max power control is done internally in the hydraulic pump with a spring whitch balances the swashplate against the pressure from the plungers in the pump. The power control is adjusted by the allen bolt above the pilot pump and I would start by adjusting it out 1 full turn at the time. If the engine still is overloaded after 4-6 turns I would suspect the hydraulic pump. If the engine load decreases and the machine is slow after 4-6 turns the engine lacks power. Make notes of how much you adjust the pump to be able to reset it.
If the machine has aircondition i suggest you check the function of the torque control solenoid valve.
I have just installed the complete hydraulic system from a zx50 into another excavator. Im pretty sure I have all the lines routed correctly multiple checking. My issue is when operating the hydraulic the cylinders will only move within the pin clearance and has absolutely no power, engine doesnt bog down or change pitch at all. It was a aircon machine and I have just capped the pc line. Do you have any ideas what might be going on? My thoughts is the smash plate in the pump isn't changing. Im just about to order a test system to test pressures.