What happens when you choke a HYD motor?

[tpulley]

I was wondering what would happen with a Hyd motor if you use a supressor (for lack of what it may be called) to limit the amount of fluid (this would result in rpm speed). From what I read it appears a hyd motor say runs a 320 rpm and can cut say up to 1.5 inch branches (using a sickle bar). If I limit the flow of fluid to say 1/6 of the speed to keep from overheating the sicklebar mower does this also reduce the strength or its ability to cut limbs?

Thank you for your help.

 

[IceStationZebra]

Potentially you will blow the motor up and won't be cutting anything. ISZ

 

[SPYDERLK]

I dont think youll have any trouble with overheating the bar at 320 cycles per minute. You should not lose appreciable torque as you slow it tho. Lowering tractor and therefore pump rpm is a good way to lower the motor speed without using a restrictor.
larry

 

[Tractor Seabee]

I was wondering what would happen with a Hyd motor if you use a supressor (for lack of what it may be called) to limit the amount of fluid (this would result in rpm speed). From what I read it appears a hyd motor say runs a 320 rpm and can cut say up to 1.5 inch branches (using a sickle bar). If I limit the flow of fluid to say 1/6 of the speed to keep from overheating the sicklebar mower does this also reduce the strength or its ability to cut limbs?

Thank you for your help.

Depends on the type of pump, reciprocating, gear, rotary vane (turbine type), or centrifugal.

Recip and gear pumps are positive displacement; when the discharge is restricted they will still continue to pump and build the pressure to the stall point or pop the relief valve, which it probably has, then keep pumping into the tank. If the relief valve works not too much probably except a lot of noise, vibration, and wear, if it sticks and the pump goes to the stall point the weakest link in the drive chain will break or stall the prime mover. Thee longer on the relief line the hotter the oil gets in the tank, that horsepower/energy is then all converted to heat not power.

Vane and centrifugal are self limiting based on the pump curve, or the relief setting which ever is higher. They will generate the heat with in the pump due to the bypassing of fluid around the impeller. They can get hot enough to burn the paint and the oil.

Lesson: do not do something that restricts the pump output to where the relief lifts regularly or consistent.

Ron

 

[Willl]

To slow it down and still regain power, I would gear down the HYD motor output shaft.

Don't slow the motor, gear down it's output.

 

[J_J]

Your hyd motor is rated for and can develop a certain HP give the flow and resistance.

The displacement in cu in, and GPM's determine the rpm.

The cu in of the motor and pressure determine the torque.

When you cut something, you are providing resistance for the motor to develop the pressure and therefore the power to cut.

If it was designed to cut a 1 in limb, and develop 2500 psi when cutting, then you could expect the pressure to be much lower when cutting 1/4 in limbs and less torque.

If you slow the motor, it will just not cut as fast. The cyclic rate is slower.

The hyd motor will generate more heat when developing max pressure.

If the sickle bar cutter was correctly designed to run at 320 rpm, it should not overheat.

If it is overheating, I would clean it, check the bolts for correct torque, lube well as noted in the manual, etc

It just might be that a hyd motor running at full volume and pressure would take more heat away from the motor.

 

[MHarryE]

Like JJ said, motor torque is displacement (cubic inches) times pressure (psi) giving in. lb. but if you slow a sickle speed you lose momentum which is a big thing in cutting something heavy. Sickle mowers are typically higher than 500 cycles per minute and don't like slow speed.

 

[tpulley]

Its hard to gage what is fast enough when you see one of them run. I saw/see some videos as well as reading from a previous poster how his unit was going too fast and over heated the unit. I believe the manufacturer states (I read this on their web site) that the blades should just be under a blur and you should be able to determine the individual action. Or something to that affect. How would one determine the speed of the motor by watching one work. Would the cycles be one to one or 2 to one as the stroke is going back and forth per revolution?

 

[DSteiner]

I was wondering what would happen with a Hyd motor if you use a supressor (for lack of what it may be called) to limit the amount of fluid (this would result in rpm speed). From what I read it appears a hyd motor say runs a 320 rpm and can cut say up to 1.5 inch branches (using a sickle bar). If I limit the flow of fluid to say 1/6 of the speed to keep from overheating the sicklebar mower does this also reduce the strength or its ability to cut limbs?

Thank you for your help.

Using one of these will give the hyd motor full torque but give you infinite control over the speed of it. Save the stress on both motor and pump.

 

[tpulley]

Cool. This I think will answer my delima. I will report back in a few months once I get it built.

Thanks guys for all the info.

Terry