hydr motor pressure limit question how to restrict power output

   / hydr motor pressure limit question how to restrict power output #1  

burntside bob

New member
Joined
Jun 14, 2010
Messages
24
I have purchased a White WR255400 hydraulic motor to power a home made rock drill and regulate the down pressure on the drill bit.
The factory representative of Kubota Tractor (the drill will mount to a Kubota mini excavator) said, the diesel engine and hydraulic pump puts out 1475 PSI at the hydraulic motor tool (the white motor) at 17-18 GPM at max engine RPM of 2800 RPM.
If I cut back the engine to 1400 RPM the GPM should drop to 8-9 GPM, this is what I want, for pulling the drill bit out of the hole via steel roller chain on drill mast.
My question is how do I limit the hydraulic force being applied to the drill bit, I mean the hydraulic motor (white WR255400) applying down pressure on the drill bit.
Would a pressure relief valve work placed in the supply line to the WR255400 hydraulic motor?
I want around 400 pounds of force from the WR255400 hyd motor on the drill bit and also (very important) use the 1,000 lb hydraulic force from the WR255400 hyd motor at 1500PSI to pull the drill and drill steel up out of the hole.
What comments and suggestions do you have?

ADDITIONAL COMMENTS: next day posted in reply to questions asked.

In reply to the posts replying to this question:
When drilling into the hole I want, need 400 pounds of down force applied to the drill bit, like placng many many concrete blocks on top of the drill to increase the force of the drill bit hitting the rock, speeding the hole drilling.
When pulling the drill bit out of the hole after the depth has been reached, I want to use all the force/power of the WR225400 hydraulic motor I can get which at 1500 PSI is about 1,000 pounds of force, this 1,000 is after having factored in the 4 inch sprocket wheels of the roller chain drive system powered by the WR255400 motors power. If PSI is reduced to 400 PSI (the factory chart for hyd motor communicates the pulling force is reduced to only 300 pounds of force, too little for my need).
On Duff's comment of using the valve levers to control the hyd oil flow, good comment, but it would result in more or less down pressure then the 400 pounds thrust force I want. Need to do something else then randomly moving the valve lever to different positons, although close to the same location each time a hole is drilled. Away that will consitently repeatably result in 400 pounds down thrust is what I need.
Also I can not reduce the PSI to the WR255400 hyd motor as I need the 1475 PSI from the excavator to get the power to pull the drill up the drill mast and drill steel out of the hole.
Need a way to regulate the down pressure on the drill bit at 1475 PSI to around 400 pounds force on the drill bit.
The Kubota engine is to be run at 1/2 throtle to get around 8 GPM flow, this will result in the WR255400 hydr motor turning the sprocket wheels at 63 times a minute which I need to control the speed of pulling the drill up out of the hole.
The only hydraulics being worked while drilling is the WR255400 hyd motor the rest of the hyd controls are not touched.
I seldom ever open the engine up wide open, don't need the power or all that hyd fluid speed it provides.
On a Pressure Reducer Value would I need a pressure relief valve or something else ?
Thank you for replying to this question, it is much appreciated and very helpfull.
 
Last edited:
   / hydr motor pressure limit question how to restrict power output #2  
Try using a Pressure Reducer Valve.
I think from reading your question, you want to reduce your pressure from 1475 PSI to 400 PSI.
The difference between a Pressure Relief valve and Pressure Reducer, is the Pressure Relief valve dumps oil back to the tank after hits the set pressure ( creating allot of heat ! ).
The Pressure Reducer valve is a regulator, and will maintain the set pressure that you want, with out dumping oil back to the tank. The valve is contantly moving, as it get its to its set pressure it starts to close. As the pressure starts to drop, it opens up, giving you a constant pressure.

As a side note:
Try and maintain RPM at its highest level ( This is not a hard and fast rule ), but if you start lowering your revs, then when the hydraulics start to work hard, then your engine is going to bog down and then stall.

Control the flow of the oil, with your valve levers. Dont open up fully, just open up a little.
If your impliments are still flying around to quick, then you can put in flow restrictors on your return oil for that impliment circuit.


Duff
 
   / hydr motor pressure limit question how to restrict power output #3  
The down force will have to come from something else, as the hyd fluid is just turning the motor. It could be a small hyd cyl, designed for low push force, or a spring force of 400 lbs. You might check the push force on the shaft end of the hyd motor to see if there will be a problem with the bearings.

A 1 in bore hyd cyl with a .5 in rod, and 510 psi will produce about 401 lbs of push force and 376 of pull force.

The GPM's will determine the speed of the hyd motor, and the pressure will determine the torque.

https://www.surpluscenter.com/item.asp?item=9-1649-04&catname=hydraulic
 
   / hydr motor pressure limit question how to restrict power output #4  
Can you show some rough drawings and some pictures of the drilling rig.

Are you using the bucket cylinder now to get the down pressure? If you are, then a gage in the cab would register the down pressure on the bucket cyl. There are electronic hyd regulators like on a laser scraper blade, that continuously adjust the pressure and raise or lower the cyl on the blade.

I have a pressure gage in the lift cyl on my PT, and at any instant, I can see what the pressure is. With no load, just bucket, very little pressure. With max load, I peak out at about 2750 psi. You can also see spikes from back pressure.
 
   / hydr motor pressure limit question how to restrict power output #5  
Ok Bob

You can put a a Pressure Reducer ( with a check valve ) on one side of the motor circuit. This will allow your pressure to be reduced to 400 PSI when drilling, but allow you full pressure to bring the drill string back out of the hole.

I have done a rough hydraulic schematic, which looks like it should do the job.
I will add some flow restrictors as optional extras, so you can adjust the speed of which you want to the hydraulic motor to turn when going up or going down with your top drive.

I just need to clean up my mistakes, scan it, do a few jobs around the house and I will send.

Duff
 
   / hydr motor pressure limit question how to restrict power output #6  
If your impliments are still flying around to quick, then you can put in flow restrictors on your return oil for that impliment circuit.


Duff

Be carefull with this, better to check max back pressure from White if a case drain port is not used on this motor (you might blow out the shaft seal with too much back pressure).....if no case drain port returning back to tank, better to use "Meter In" rather than "Meter Out" to slow things down.....

Bill:)
 
   / hydr motor pressure limit question how to restrict power output #7  
Hi Bob

I have done the one schematic in the nuteral, down and up position.
I have tried to colour in the different pressure oil to help you get a understandng of it.

In the schematic, Im assuming;
1/ you have fixed displacement gear pump
2/ you have a fixed displacement gear motor
3/ Your relief valve is set at 1500 PSI ( as you have mentioned )

I have added flow restrictors, so that you can adjust your speed for up and down.
I have not added return filters on the schematic, but Im sure there on your system.

OK, Im sure there will be critisim or quirey's, will do my best to answer all, time permitting.

Duff
 

Attachments

  • Top Drive Nuteral Position.jpg
    Top Drive Nuteral Position.jpg
    23.1 KB · Views: 202
  • Top Drive Down.jpg
    Top Drive Down.jpg
    34.9 KB · Views: 268
  • Top Drive Up.jpg
    Top Drive Up.jpg
    31.1 KB · Views: 206
   / hydr motor pressure limit question how to restrict power output #8  
Be carefull with this, better to check max back pressure from White if a case drain port is not used on this motor (you might blow out the shaft seal with too much back pressure).....if no case drain port returning back to tank, better to use "Meter In" rather than "Meter Out" to slow things down.....

Bill:)

Hi Bill

If its a piston motor, then it will have to have a case drain ( and it should not be blocked, or it will blow a seal ! ) But you can put flow restrictors on the return side, as the shaft seal does not see full pressure ( Unless your pressure plate in the motor has had it !! ).
If it is a gear motor, it should not matter too, because if the motor is stalled out anyway, it must be capable of taking full pressure ( 2500 PSI ).

You had me thinking on the reason why manufactuers always put there flow restrictors on the return side. As having a flow restrictor on the pressure side would work too.
But I think it comes down to effeciency. The pump/ engine ( more fuel ) would have to work harder to do the same job, because the oil would have to get through a restriction 1st before it had to do its job, at the actuator.

With the flow restrictor on the return side, the oil would do the work at the actuator 1st ( with out any restriction ) before its restricted on the way back to tank.

However your right, when your using flow restrictors, you must be careful how much you restrict the oil, as in cylinder circuit, you can get "pressure intensification" and blow hoses etc.

Cheers
Duff
 
   / hydr motor pressure limit question how to restrict power output #9  
You had me thinking on the reason why manufactuers always put there flow restrictors on the return side. As having a flow restrictor on the pressure side would work too.

If inertia and/or gravity can make the motor move/drift, meter out restriction (return side), will cure that problem

If motor is designed for bi-directional use, a meter out restriction should be ok.....
(reservation for meter out restriction on extending a double action cylinder, calculate the back pressure before final design)


Btw....You did some great drawings and it all looks good to me....:thumbsup:
 
   / hydr motor pressure limit question how to restrict power output #10  
Duff,

yea efficiency is probably why they do it....(Meter out)....I also think they use meter out to prevent boosting to smooth out the flow.....but I guess I'm used to using case ports for that cuz by the time I see um they're blown out,

Some motor mfg's have case ports built in (tho you don't need them with no BP), all you need to do is remove plug and run a line to res....I always use case drain if avail on multiple motors in series (upstream motors only)...

Also the OP mentions White Hyd Mtr....you mentioned Piston Motor? Never seen a White Piston Motor....usually the White's I've seen are geroler motors and can take a stall at high pressure but no need for case drain..

Also Gear motors can also stall at high pressure with no trouble but not back pressure of same.....Yikes .....:confused2:
 
 
Top