[Phil P]

MIMF

The hydraulic system in my trailer returns the fluid from the pressure relief valve directly in to the pump inlet port not the fluid reservoir. Under an extended run this will over heat the fluid. I have seen operators hold or have a control fail and do nothing about it until the unit caught on fire.

I have had mine apart to see about increasing the sizes of the reservoir so I could add hydraulic landing gear.

Your pressures are common to most industrial systems. Addition of cylinders of the same diameter would not necessarily require more pressure but defiantly would require more volume. You could double the number of cylinders with out increasing the volume by reducing the diameter of the cylinders. That may require more pressure unless the multiple cylinders are lifting the same gross weight. IE 2 cylinders lift 4,000 lbs and you increase the number to 4 cylinders of a smaller diameter but still lift only 4,000 lbs would require the same pressure. The reduction of size will have to be calculated to determine what reduction in sizes would make this work.

That 12-volt motor would go off like a flash bulb if it ever drew 100 amps.

The wiring to my unit is AWG #4 rated at 60 amps. This is the larges fuse / breaker that should be installed in this line regardless of what size motor you are trying to operate. (REF: Table 1 American Wire Gage cable / conductor sizes and properties copper conductor)

I agree with the OP that if his unit worked without tripping the breaker of 50 amps and now he is unable to make pressure relief without tripping the breaker then he has a problem that needs to be addressed. If he decides to increase the brake potential and he has determined the wire sizes to be AWG #4 then he should not go larger than 60 amps. (REF: Table 1 American Wire Gage cable / conductor sizes and properties copper conductor)

I agree with the OP that if in fact the motor will draw 100 amps and the wiring is not at least AWG #1 increasing the breaker to 80 amps is a fire hazard. (REF: Table 1 American Wire Gage cable / conductor sizes and properties copper conductor)

How ever in spite of this my system is protected by a 50-amp breaker and has never tripped the breaker and when I extend or retract the slides I run the pump until I hear the pressure relief valve open.

One time we had a wine rack get behind on of the slides and the hydraulics are so powerful that it pushed the front lip off the slide without ever loading the pump to pressure relief. This indicates that a slide would have to be severely binding to cause the pump to reach pressure relief with the slide only part way open but would not result in the breaker tripping unless there is a problem with the electrical system or motor.

It is still established by the engineers and training standards that the breaker is there to protect the wire not the motor.

Phil P