Hydraulic Motor

   / Hydraulic Motor #1  

Jw5875

Gold Member
Joined
Aug 27, 2005
Messages
414
Location
NW Pa.
Tractor
Kubota L3400
What keeps a hydraulic motor from "Free Turning" when the control is set in neutral? Is there a check valve built in or a brake?

Curious mind!

JW 5875
 
   / Hydraulic Motor #3  
Yepper and pressure is just a few psi (low pressure mode on a 2 stage) with the open center control as viewed on the pressure meter at the entrance to the return filter attached to the reservoir.
 
   / Hydraulic Motor #4  
Some have counterbalance valves, some internal .......most times the control valve a & b ports are blocked in neutral
 
   / Hydraulic Motor
  • Thread Starter
#5  
Thank You Gents for the info!

Inquiring mind at age 68 -------Goals:

1: Wake up every day
2: Learn something new every day
3: Make some one smile every day

JW 5875
 
   / Hydraulic Motor #6  
What keeps a hydraulic motor from "Free Turning" when the control is set in neutral? Is there a check valve built in or a brake?

Curious mind!

JW 5875

Depends on the application and circuit.

Some examples:

Simple circuit like post hole auger can have a valve with the A & B ports blocked in neutral or can have a motor spool with A & B & T ports all connected together. Typically running slow with limited inertia.

On a wheel application like used on a scissor lift it may have counter balance valves and a brake to prevent free wheeling. You don't want the lift to run away while on a slope.

On hydraulic fan drives where there is high speed and lots of rotating mass they almost always incorporate a "run down" feature to prevent stopping the motor to quickly.
 
   / Hydraulic Motor #7  
"On hydraulic fan drives where there is high speed and lots of rotating mass they almost always incorporate a "run down" feature to prevent stopping the motor to quickly."

This can be a check valve across the motor to allow the motor to keep spinning, a hydraulic spool with A and B connected in neutral (aka motoring spool), an anti-cavitation valve, low pressure relief after the motor, etc. This applies to any hydraulic motor with a lot of inertia like mowers, fans, etc.

And as far as not turning in neutral don't forget that some systems naturally have a lot of friction. Think track drives, worm gearboxes....

ISZ
 
   / Hydraulic Motor
  • Thread Starter
#8  
"On hydraulic fan drives where there is high speed and lots of rotating mass they almost always incorporate a "run down" feature to prevent stopping the motor to quickly."

This can be a check valve across the motor to allow the motor to keep spinning, a hydraulic spool with A and B connected in neutral (aka motoring spool), an anti-cavitation valve, low pressure relief after the motor, etc. This applies to any hydraulic motor with a lot of inertia like mowers, fans, etc.

And as far as not turning in neutral don't forget that some systems naturally have a lot of friction. Think track drives, worm gearboxes....

ISZ


So in theory, you could run a hydraulic motor in place of a log splitter cylinder on a log splitter?

JW 5875
 
   / Hydraulic Motor #9  
Everybody is correct but to keep it simple; It depends on the motor design and the design of the equipment. Some will free spin when fluid flow stops and require a brake to stop. Others will stop when fluid flow stops but they will act as a pump if rotation force is applied. Various methods are used on these motors to "run down" or relieve back pressure. Still others are allowed to lock when flow stops.
 

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