Originally Posted by Grumpy Grampa
Thanks. I have the four hydraulic lines for each jack coming off the pump. What are the orange hoses coming off the pump, next to the four hoses?
Before CV-19, the high pressure lines to raise the coach were orange and the low pressure return lines were blue, now it appears all may be orange. Although the system raises the coach in pairs it lowers all jacks together, therefore there are only two return lines for the coach. The return lines are joined in pairs at the front and rear of the coach.
The way the systems works in auto follows:
The computer located in the center of the coach above the drive shaft, senses an out of level situation and computes leveling sequence. The computer starts with the greatest tilt. Although the system works with pairs of rams when lifting, it grounds each jack separately. Grounding is necessary, so that the coach is lifted squarely. After the first two jacks are grounded, the computer direct oil into the tops of both rams at the same pressure until the computer senses the coach is level in that cardinal direction.
Hopefully only one more jack needs to the grounded to complete the leveling. After that jack is grounded that pair of jacks (one is from the previous lift sequence) pressurized to level the coach. To stabilize the coach the fourth jack is grounded and the computer waits for 10 to 15 seconds to check the coach level, as a jack may have settled into the soil or gravel. If the coach is out of level and can be correct by continuing to level using the the previously used jacks the computer will raise or lower the rams as needed. If the fourth jack is involved the coach must be raised.
This sequence uses the minimum amount of movements. If the coach is parked racked, that is one wheel very high or low when compared to the others this will require to additional jerky movements to square and level the coach. There can be up or down depending on the computers calculations. Fluid in the bottom of the ram (below the seal) is returned to the tank through the two return lines and is not under pressure.
The retraction sequence is entirely different. The four lifting valves are opened allowing the coach to settle onto the springs. The fluid is returned to the tank by the high pressure lines, but it is not under pressure. The pump pressures the two return lines that go to the bottom of the rams forcing the ramps into the up position. When the pressure in the return lines reaches 1,500 psi, the pump stops and the computer assumes all jacks are up. Should the return line pressure drop to 1,300 psi the pump will start to pressurize the return, and turn on the warning tone and indicate there is a jack error.