I'm trying to modify a rotation gearbox on a boom truck. It currently has an integrated brake inside the gearbox that's spring applied (looks like a motorcycle clutch) and pressure released when you actuate the cw or ccw control lever. What I want to do is disable this internal brake and fabricate a manual foot operated external brake. If your familiar with cranes you'll know what im talking about. There's a list of things i'm trying to figure out. I need this geroler motor to be able to free spin when the shaft is under a load and the control lever is in the neutral position and not have the shaft snap or any other bad things happen. If I can figure out how to do that successfully, everything else will be fairly straight forward. I'm not sure exactly what these relief valves mounted to this manifold block are for? and are they are going to prevent this motor from free spinning? Note... The JIC fitting is just the pressure port that releases the internal brake. There's one for each port. I thought they might have been cross port reliefs but doesn't that mean the over pressure would blow into the opposite port? If so I can't see how that could happen, i took that thing all apart and looked it over for quite a while. They seem like they could completely stop the flow of oil into the motor if the oil got to the preset relief pressure but it doesn't appear to have an exit out of this manifold block if that happens. It's almost as if it stops the oil flow and then the relief valve back at the control valve would open to let the pressure back to the tank. But if that's the case why would you need these relief valves at all? What am I missing here? The next issue is the spool. The way it's setup right now, both ports are blocked off and do not return to the tank when the control is in neutral. I'm thinking I need to have a new spool made that would be open to the tank on both lines when the control is in neutral right? Any thoughts or advice is appreciated!!!
Does this boom truck handle/lift personnel?
nope, its a "crane" boom truck not a "cherry picker" type boom truck. A terex RS70100 to be exact.
The cartridge valves are most likely internal pilot counterbalance valves, they require internal pilot pressure to release them and allow oil flow, pretty common on hydraulic motors, and one of their purposes is to prevent "free rotation" or "runaway" of the motor, they require pressure input to the motor to make it turn. Not much of a way that I know of that you can modify or disable that with the configuration that you have. I don't know what you need to achieve what you wish to do, make a free swing boom with a foot brake, but whatever would make that happen would require an anti-cavitation system for both A and B ports when the control lever is in neutral and the boom is free swinging.
If I need to buy a different motor that doesn't have these valves on it I will certainly do that. What do you mean by "anti-cavitation" system?
I put 20 psi of air into those threaded hydraulic fittings where the hoses would be supplying oil for right or left operation and the valves opened. I couldn't get them to open from the other direction, seems like they are more like a check valve ?? But how would that work, if oil is going into the motor from one port it has to exit through the other port. Why would there need to be a valve on the exit side that doesn't open until a high pressure is met??
Any motor can be turned into a pump if enough external rotational force is applied to the output shaft. Say you have a large load swinging to your right slightly down hill. The force would try to pull more oil into the input port and create a suction on that circuit. The anticav valve on the output side would sense the zero value or suction value and close down the flow returning to tank to keep the load from running away. I would have to see a schematic of the block to see if removing them were possible. I'm guessing that removing the cartridges would allow all the oil to bypass the motor completely What you are describing that you want to do is have a free swing with a manual brake system. A free swing would require a motor spool in the supply valve. A motor spool in neutral allows oil on either side of the motor to be open to the hydraulic tank through the spool. The swing brake you are describing is a parking brake only. If it is in the block that you are showing, it is likely internally ported. That kind of a brake is usually only applied or released. There is no feel in it. You might talk to the manufacturer of the crane or at least the dealer about what you want to accomplish. Early in my career I had to run a P&H rough terrain crane that was set up as you describe. What I note about that crane is that free swing in a hydraulic unit is to mimic a friction crane. That is the last thing I ever wanted in something where I had to do some very precise landing of extremely heavy loads. When loading counterweights on the backs of large crawler cranes, the free swing feature tended to allow the counterweights to try to get away before the mounting bolts could be installed. The manual brake had to be used at the same time as the swing making it hard to get that fine movement exactly right.
When you grab the lever to swing, it likely raises the pressure in the line, so that it releases the brake first, before it allows it to swing. Otherwise you would be dragging against the spring applied brake all the time, with the swing motor pushing against the brake, before it had enough pressure to overcome the spring brakes. I was around one attempt at making a boom truck swap, from friction swing to free swing, and I don't think it ever did work correctly. With terex gone, the only help you're going to get "factory" wise is from load king in kansas city- they have all the old terex stuff. Aren't you glad you saved money buying terex instead of national? Is there a big planetary reduction box below the brake, before the swing gear? or is it straight brake to rotec? I haven't been around a 70100, just the older simon stuff that became terex. In fact, I think it was a simon that a guy I used to work for, tried to convert. Regardless, I'm guessing you're sick of friction swing, and want free swing, I'm going to suggest you just ditch the terex, and hope there's a buyer who doesn't know what they are looking at, and go national or manitex and don't look back. If that's not what you want to do, I can post up some pictures of how some different free swings are plumbed, and maybe you can work around it. You should be able to use the existing spring brake with just a 12v solenoid controlled valve, that would apply hyd. pressure to push off the springs, and let the hydraulic off to allow the springs to apply. That's the way the old nationals work. The brake is separate from the swing hyd. Some guys really like friction swing and get used to it, I've always preferred free swing.
Which is how I suspect it works, and which is why I suspect those cartridge valves are internal pilot operated counterbalance valves. The valves "lock" the oil inside the motor. When you apply pressure to one input port, take port A for example, the motor doesn't turn because the counterbalance valve on port B has the oil blocked, you have to develop a certain amount of pressure input on port A for the internal pilot line from port A to "unlock" the counterbalance valve on port B, this also gives you the needed pressure to release the brake through a shuttle valve between port A and B lines going to the brake.
Typical motor application with internal pilot operated counterbalance valves and shuttle valve for brake release.
And as John C mentioned, a free swing boom typically uses a control valve spool that has both lines connected together when the valve is in neutral allowing the oil to loop, and sometimes it's connected to tank line in neutral to provide anti-cavitation through the check valves at the motor
Typical rotate motor control valve. The two lines on the top are the pressure output lines to the motor. The line on bottom left is pump pressure, the line on bottom right is tank. When valve spool is in neutral the two output lines are looped together and both are connected to tank for anti-cavitation.