Importing and modifying a new mini excavator from China

[oldrustysteel]

Hello All. I'm new to the group. I just finished reading the comments from start to finish and wished I had done so before picking up my AGT L12 at auction about a week ago. I paid $4225 plus auction fees and sales tax for a total of about $4925 out the door. There were 22 AGT units up for auction, only 2 L12's, a couple of H15's, and the rest split between H12's and QH12's. All of the units went for low $4000's except for the H15's which were low $5000's.

I liked the L12 because of its openable "hood" and that it comes with a hydraulic cooler. Sadly, no spin on hydraulic filter, which I plan on remedying asap. The lcd hour meter was full of water and no functional, since replaced with an electric/mechanical style. The digging force is very weak, I hope due to the relief valve being set too low. I cranked it up a bit and it seemed to help, but don't want to push it until I can get the adapter to get a gauge on it. I've already been ejected from the drivers seat, picking up a pretty good hunk of freshly cut firewood and pivoting sideways. She's a tippy one.

Congratulations on the L12. I really like mine. You got a good price IMO.

 

[dfkrug]

I've already been ejected from the drivers seat, picking up a pretty good hunk of freshly cut firewood and pivoting sideways. She's a tippy one.

First, welcome to TBN.

Ejected? Did you tip over?

Good to see you already flipped your boom cylinder around to protect the hoses. Or did it come that way?

 

[gmbaird]

First, welcome to TBN.

Ejected? Did you tip over?

Good to see you already flipped your boom cylinder around to protect the hoses. Or did it come that way?

It came the way you see it. Yes, I tipped over and slid off of the seat onto the ground. I was partially rotated and the machine came to rest on the bucket still clutching the big chunk of sugar maple. Scared the crap out of me, but thankfully no injury. It was pretty easy to upright the machine by hand.

 

[JamesTheNextDoor]

What about locating 2 crossover RVs or counterbalance valves inside the house to protect the wheel motors? Not ideal location on the motors, but there is room inside, and adapting to wheel motor near the valve is not hard.

As you know, it's best to position the RVs as close to the motor as possible for optimal performance. In theory, connecting the RVs to the motor using metal piping helps minimize pressure drop. In small equipment operating at 2400 psi, hose connections may not present issues. However, one may have to sacrifice one of the advantages of the counterbalance, which is holding the actuator even during hose failure. Additionally, I'm a bit concerned about the swivel joint in the middle of the line.
So, there are some drawbacks, I can't be sure, but it seems like it'll work.

 

[USMC43]

See my post #100.

Congrats on the EM15.

You have another option since you have servo (pilot) controls. You can do the swap on the main valve, or you can swap hoses in the arm rests. You need to open up the machine anyway to tighten bolts, adjust the main relief valve, sleeve hoses that rub, and see what you got.

In particular, check for hyd return filter(s) under the floor panel.

Pilot operated controls via a joystick doesn't equal servo. It seems you have used that terminology a lot in this thread. 16 years working for Cat, most of it hydraulics, I have never heard pilot pressure valves referred to as servo valves.

Newer name brand excavators do use servo valves. They are electronic controlled pilot pressure valves. Servo implies that something has feed back. The controller(machines computer) receives input from the operator via a potentiometer in the joystick. It then sends a current to the valve to operate the valve.

An LVDT sensor mounted internally in the valve sends feed back to the machine so the computer can determine if it was successful in its command and tweak the power to achieve the result desired if not via a closed loop.

Industrial hydraulics do something similar but there is typically a controller card that handles the direct control of the valve and the PLC just sends the card the desired function but leaves the feedback loop to the card. They are typically referred to as proportional valves in industrial world.

Both are touchy to contamination (2 micron pressure filters typically used)

 

[dfkrug]

Pilot operated controls via a joystick doesn't equal servo. It seems you have used that terminology a lot in this thread. 16 years working for Cat, most of it hydraulics, I have never heard pilot pressure valves referred to as servo valves.

First, welcome to TBN.

I deliberately used the term "servo" to describe what are usually called "pilot-operated" valve. The term, servo, short for servomechanism or servomotor describes a system that uses a secondary power source to operate a primary power source to operate a device that does work. Usually, some form of feedback of the position of the secondary mechanism is involved. That feedback could be electrical, electronic, hydraulic, or even visual. Without this feedback, we would have what engineers call an "open-loop" system.

In our excavator, we have an operator-controlled lever, that controls a small spool valve that supplies hydraulic power to the the spool of a larger primary valve, which then spins a motor or moves a cylinder. Feedback is visual, as the operator feathers the joystick valve control to proportionally move the secondary valve spool.

In industrial fluid power, secondary control can be hydraulic, electric, electronic (proportional or on-off), even pneumatic. As in any industry, there is a lot of jargon. It seems to me that the term servo (as in servant or slave) may be clearer to outsiders than "pilot-operated".

 

[jaylast]

Pretty interesting I've always associated servo / servomechanism as having to contain electrical mechanical elements of separation / control (from user and/or from the rest of 'circuit')

Personally for myself it was slightly confusing to refer to simple hydraulic pilot controls as 'servos' but after the explanation and some reading I suppose technically servo in this sense could describe the simpler hydraulic pilot system, using visual feedback and the actual operator as the electro mechanical aspect.

There could also be instances of cable (or other rudimentary means) pilot controls?
Best to use servo pilot, hydraulic pilot, or mechanical/air pilot etc as they fit best? . . . But i'd have to say technically 'servo' could also describe all in these circumstances.

I'm in the camp that 'language constricts thought', not the inverse, so always fun stuff.

 

[USMC43]

First, welcome to TBN.

I deliberately used the term "servo" to describe what are usually called "pilot-operated" valve. The term, servo, short for servomechanism or servomotor describes a system that uses a secondary power source to operate a primary power source to operate a device that does work. Usually, some form of feedback of the position of the secondary mechanism is involved. That feedback could be electrical, electronic, hydraulic, or even visual. Without this feedback, we would have what engineers call an "open-loop" system.

In our excavator, we have an operator-controlled lever, that controls a small spool valve that supplies hydraulic power to the the spool of a larger primary valve, which then spins a motor or moves a cylinder. Feedback is visual, as the operator feathers the joystick valve control to proportionally move the secondary valve spool.

In industrial fluid power, secondary control can be hydraulic, electric, electronic (proportional or on-off), even pneumatic. As in any industry, there is a lot of jargon. It seems to me that the term servo (as in servant or slave) may be clearer to outsiders than "pilot-operated".

The dictionary defines servo as-"

1. A feedback system that consists of a sensing element, amplifier, and servomotor, used in the automatic control of a mechanical device.
2. A self-regulating feedback system or mechanism.
3. An electronically controlled mechanical or hydraulic device permitting a large action or strong forces to be controlled by a small electrical signal."

If you say the operator functions as the feedback mechanism, then all valves, say a standard spool valve, or even simple gate/ball valve are servo valves by your attempt to define it having the operator act as the feed back mechanism in contrary to the definition.

Yes there is a lot of jargon, and no one in the industry calls manually operated "pilot pressure valves" "servo valves" because it makes it unclear what your talking about.

This is due to higher cost construction equipment for the last 20 plus years does actually use servo valves with electronic feed back mechanism and electronic joysticks as the user interface with the operator.

 

[USMC43]

I'm in the camp that 'language constricts thought', not the inverse, so always fun stuff.

In this case it doesn't constrict thought at all, it clarifies it. Doesn't make it so muddy.

Caterpillar standardized on pilot operated hydraulics in the 70's. They were the first to bring it across the line on their equipment and by the early 80 nearly everyone else in the construction industry had followed suit.

50 years of nomenclature shouldn't be thrown out on a whim.

 

[dfkrug]

The dictionary defines servo as-"

1. A feedback system that consists of a sensing element, amplifier, and servomotor, used in the automatic control of a mechanical device.
2. A self-regulating feedback system or mechanism.
3. An electronically controlled mechanical or hydraulic device permitting a large action or strong forces to be controlled by a small electrical signal."

I think #1 or #2 support my usage of 'servo'.