Valve to control hydraulic motor

   / Valve to control hydraulic motor #1  

Popeye1

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I have an old skid steer (Bobcat 610) It is belt drive with 4 clutches. The clutches are getting worn and I would prefer not to replace all of them since it would be more than I paid for the skidsteer.
I am considering connecting a hydraulic motor to the drive system on each side and bypassing the old drive system completely, this would also allow me to use a variety of engines if mine ever needs replaced.
I know that ideally I would get a hydrstatic pump, or variable displacement pump. However, this is a project to SAVE money, not spend it.
I already have several gear pumps and a vane pump that I have salvaged from other machinery. I also have several matching spool valves (Gresen 400).

Question:
Can I use regular spool valves or do I need something with a variable control in order to get fairly smooth operation? What would you recommend? I am just afraid it will be stop or full speed with these valves and was hoping for opinions.

Remember, this is a 40 year old machine, so I'm not expecting it to operate like a cadillac, just functionality and safety.
 
   / Valve to control hydraulic motor
  • Thread Starter
#3  
Any idea how the flow control would be with those valves? How jerky? I see that they can be open or closed center. Does that mean I could make it hold/brake the motor when the valve is in center like a hydrostatic?
 
   / Valve to control hydraulic motor #4  
   / Valve to control hydraulic motor
  • Thread Starter
#5  
If I understand correctly, A regular spool valve (not motor spool valve) will not allow the motor to freewheel? Is it correct that motor spool valves essentially have a float between the two lines when it is in center position?
 
   / Valve to control hydraulic motor #6  
That is true.

You could use an open cyl spool valve, but it would be jerky. When you released the valve it would stop/brake.

Your best bet is a hydrostatic transmission for smooth operation.

What size engine is in your machine?
 
   / Valve to control hydraulic motor #7  
That is true.
You could use an open cyl spool valve, but it would be jerky. When you released the valve it would stop/brake.
Your best bet is a hydrostatic transmission for smooth operation.
What if you put in a crossover relief valve such as Surplus Center - 1/2 NPT 30 GPM 1500-3000 PSI HYD CUSHION VALVE or Surplus Center - 3/4 NPT 30 GPM 1500-3000 PSI HYD CUSHION VALVE with a spool valve. That would allow it to "coast" to a stop but would slow/prevent creeping when in "neutral".

Aaron Z
 
   / Valve to control hydraulic motor
  • Thread Starter
#8  
Would I need one of those in each line (two lines per motor)? That would mean four of those little suckers if I only used two pumps.

The engine is 30 HP.
 
   / Valve to control hydraulic motor #9  
Popeye,
How smooth you start and stop depends some on the valve metering capabilities and some on the operator. If you move the valve to fast you will get sudden changes in flow.

Another problem you will have is load changes on the drive motors will potentially radically change the motor speed since these valves are not pressure compensated. More expensive mobile valves have pressure compensation for each valve section and typically better metering characteristics. I.e. Rexroth M4-12 , Sauer Danfoss PVG, etc.

I suspect you will also discover that your tractive effort (ability to do work) will decrease by 15% or more Vs the belt drive.
 
   / Valve to control hydraulic motor
  • Thread Starter
#10  
oldnslo,
Thanks for the insight on that. I imagine that without spending a lot of money (almost enough to upgrade to another skidsteer), that the controls will take some getting used to.
Good point on the loss of power due to efficiency, I will have to really think this through.
 
 
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