Needle valve vs. motor spool

[teg]

I don't have a motor spool but would like to power a hydraulic motor using a spring to center spool with detent. I was planning to use the valve in detent with a needle valve to start and stop the motor (I don't mind if it's slow).

I would have the needle valve closed, put the valve into Detent mode, open the needle valve slowly until the motor was at the right speed. Use it and when I'm done dial the needle valve down until it closes, thus slowing the motor down gradually.

The Motor I'm planning to use is: https://www.surpluscenter.com/item.asp?item=9-1365&catname=hydraulic
Specs are not ideal: the PSI is 1,200 Max.!!! and 5,000 RPM @ 6 GPM Max!

Tractor is L2800 hst with 2400 psi and 6.5 GPM. I can not reduce the PSI on the valves.

My questions are these (along with my guess, following it)

1) If I run the tractor at lower rpms, I should have less GPM, correct? (my guess, yes and I don't think flow will be the issue, pressure might be.)

2) Does a needle valve reduce the pressure so I don't have to worry about the 1200psi spec? (needle valves do reduce flow and the motor should not allow pressure to build up, it will just run, so again yes? I hope?)

3) Main problem with this project is the motor will NOT be able to "free wheel" if the valve shuts off, (motor spool will allow it to coast to a stop) I could blow a hose with the motor shutting off quickly.... Is there anything I can do to help with that? (my guess, No, I just have to be very careful).

4) Any problem using 1/4" hose for this build? (should be fine?)

Thanks for your time and looking forward to the replies...

 

[J_J]

Just add a relief valve across the hyd motor.

This is a flow control valve with flow adjustable from 0 - 8 GPM, and adjustable relief.

http://www.surpluscenter.com/item.asp?item=9-064-38&catname=hydraulic

Full tractor hyd flow is flowing through this valve, and you are setting the flow for the rpm you want.

Needle valve does not adjust pressure.

If you use the detent valve with the needle valve closed, the relief would activate.

The hyd motor can build up to your tractor pressure as it gets to work harder until it stalls, and the relief would go off, or fluid would bypass in the motor.

 

[oldnslo]

I don't have a motor spool but would like to power a hydraulic motor using a spring to center spool with detent. I was planning to use the valve in detent with a needle valve to start and stop the motor (I don't mind if it's slow).

I would have the needle valve closed, put the valve into Detent mode, open the needle valve slowly until the motor was at the right speed. Use it and when I'm done dial the needle valve down until it closes, thus slowing the motor down gradually.

The Motor I'm planning to use is: https://www.surpluscenter.com/item.asp?item=9-1365&catname=hydraulic
Specs are not ideal: the PSI is 1,200 Max.!!! and 5,000 RPM @ 6 GPM Max!

Tractor is L2800 hst with 2400 psi and 6.5 GPM. I can not reduce the PSI on the valves.

My questions are these (along with my guess, following it)

1) If I run the tractor at lower rpms, I should have less GPM, correct? (my guess, yes and I don't think flow will be the issue, pressure might be.)...

Yes, lower RPM equals lower flow.

2) Does a needle valve reduce the pressure so I don't have to worry about the 1200psi spec? (needle valves do reduce flow and the motor should not allow pressure to build up, it will just run, so again yes? I hope?)

No, a needle valve will not reduce the pressure. For this you will need either a pressure reducing valve or a relief in the motor circuit.

3) Main problem with this project is the motor will NOT be able to "free wheel" if the valve shuts off, (motor spool will allow it to coast to a stop) I could blow a hose with the motor shutting off quickly.... Is there anything I can do to help with that? (my guess, No, I just have to be very careful)

Yes, you can install a check valve between the motor ports. This will allow oil to travel from the "tank" port of the motor the "pressure" port of the motor during run down. NOTE: Tank and pressure are during normal operation.

4) Any problem using 1/4" hose for this build? (should be fine?)

What RPM do want the motor to operate at or worded another way, what is the flow required in GPM? 1/4" hose will only flow 1.5 GPM at 10 feet/second. 3/8" hose will flow 3.4 GPM.

Thanks for your time and looking forward to the replies...

Your welcome

Roy

 

[J_J]

Have you considered getting a motor spool valve with 3 position detent like this?

Surplus Center - 1 SPOOL 8 GPM PRINCE MB11C5C1 MOTOR SPOOL VALVE

You could also use a flow control valve with relief