Running a Hydraulic Motor - Valve Question

[ddivinia]

I used a hydraulic motor for the first time this weekend. I have a John Deere 5525 and a Grassworks Weed Wiper. I had to rig a bungee cord to hold the lever in the proper position to run the motor. Is there any difference between that bungee cord I have and having to pay $1500+ for the deluxe valves with the selectable motor option? I know that on the deluxe version valve 1 has a flow regulator. The weed wiper has one, so no biggie.

I can live with the bungee cord - I just want to make sure I am not hurting anything. Next time, I am getting the deluxe valves. I didn't know they existed when I bought my 5525.

Thanks,
D.

 

[john_bud]

No direct knowledge of the JD valves, but in general...

When running a hydraulic motor, you have to remember that it is really a pump in disguise. So, if there is a lot of rotational momentum (like a rough cut mower), the motor will keep turning from that momentum. You stop the flow of fluid to the motor it can't instantly stop. It will then start acting like a pump, but the lines will be deadheaded with no relief. If the momentum can provide enough instant engery, the pressure can get very high very fast and "bad things" may happen.

Motor spool valves allow for free wheeling in neutral. Standard spool valves don't. At a guess, the "deluxe" valves may have a relief built in? You may want to add a relief valve between the inlet and outlet of the motor for protection.
Fairly cheap and easy to do. Parts from surpluscenter.com.


jb

 

[DRL]

jb is right about the motor valve. Another way is use a cushion valve at the motor, then you can get away with a regular valve. A cushion valve is nothing more than 2 relief valves in 1 housing so the motor can be protected when turning ether direction. Be nice to have detents instead of the bungee.

DRL

Surplus Center Item Detail

 

[Soundguy]

Yep.. detents. and the freewheel.. though, if the motor has an ORC installed.. it won't be an issue. One thing good about htedetents.. is if a stoppage is encountered.. most valves with detents will auto - center.. etc. With the bunji.. you may / will be running against relief.. etc.

soundguy

 

[RickB]

The bungee will work just fine, save your money. Farmers used orbit motors for 25 years before anyone knew what a motor control valve was or put one on a tractor. The concern about shock loads when stopping are valid, but can be mitigated by using a zero pressure return (in the hydraulic fill tube on a 5520 not sure about a 25) rather than the existing SCV coupler for return oil. That solution should run about $100 unless the fitting is already in your fill tube, then it's less. Alternatively, use the "lower" postion of the SCV control to power the orbit motor and shift it to "float" to stop rather than neutral. Either solution is cheap and effective unless you require the motor to run both directions. Then a crossover relief is the best solution for your present setup. Detents set above relief (as in motor spools) are fine until you forget to reset them for common cylinder use; then they are a liability and can damage pumps if the valves do not return at the end of the cylinder's stroke.

 

[Soundguy]

I like the float idea.. whoever I'm assuming not everybody has a float setting that opens both ports... My deluxe remotes on my NH do.. but my older ford remotes.. detent or not don't. I'm sure there is variance all over the board between remote setup... however.. if the motor is 1-way.. and ORC coupled int he driveline will make all that no problem..

soundugy

 

[RickB]

The zero pressure return for applications requiring only one direction of rotation is actually more foolproof. Instantly stopping flow on the pressure side is of no consequence; the problems start when the return is suddenly closed.

 

[Soundguy]

Sounds like it would be akin to deadheading a pump if the motor had a heavy inertial load and NO ORC protection. if the return was blocked suddenly.. ( and no relief on the output was present).

Soundguy

 

[RickB]

Sounds like it would be akin to deadheading a pump if the motor had a heavy inertial load and NO ORC protection. if the return was blocked suddenly.. ( and no relief on the output was present).

Soundguy

I'm not picking on you, Chris, really. I just can't develop any enthusiasm for your mechanical answer to a hydraulic concern. It is just one more frigging thing to have to design into an implement or whatever that someone else has presumably done at least a fair job of engineering. The vast majority of off-the-shelf hydraulic motors in applications germain to this discussion would have round, keyed shafts of one inch diameter or possibly a little more. Never have I seen one with a 1-1/8" or 1-3/8 " six splined output shaft. So we get to adapt a round keyed shaft on the motor to a splined shaft to accept our ORC that just cost us $45-$60. Then we get to adapt the ORC's output BACK to the round, keyed drive coupler the implement had to accept the motor to begin with. Go find one or two orbit motor applications and check out what would be required. Makes a zero pressure return or crossover relief look pretty inviting IMHO. BTW, you are missing out on the 9 inches of snow I just had to blow out of my drive up here.

 

[DRL]

You could just put a check valve between the IN and OUT lines to the motor and do the same as an ORC.

DRL