best way to reduce 200 bar to 100 bar? 1

[NL4L1F3]

Hello,

I am working on a project that uses the hydraulic pump of a tractor. The tractor has a openloop-system that has a pressure of 200 bar, with a flow of 52.5 L/min. I would like to power 2 hydraulic motors with a high RPM. I have 2 motors that have a working pressure of 100 bar each, that are otherwise perfect for the job. What is the best way to connect these to the system?

Thanks in advance

 

[HPost]

Do you really need to reduce the pressure?

If the motors are only working up to 100 BAR, then that is all they need and system won't deliver more than needed.

If you want to limit the motor pressure to protect them against occasional over pressure, then use cross line relief valves.

You would only really need to reduce the pressure if your motor circuit is likely to stall out frequently or if the down stream circuit is a closed system. In this case you would use a pressure reducing valve. However, controlling pressure at that flow rate will require a big valve.

You need to question whether you really need to reduce the pressure or just limit it.

 

[NL4L1F3]

thanks for the fast response!

A bit more information: this is the motor i was talking about:

https://www.kramp.com/shop-de/en/940241/495059/0/Orbital+motor+type+OMM.

it says the continuous pressure is 100 bar, with max pressure of 140bar (10% of the time) and 200 bar peak.

The pump compensates pressure using load sensing.

If i understand this correctly: If i were to connect this motor to the pump, the pump will sense it only needs 100 bar and not use anymore? even though the system pressure is 200 bar?

 

[hydtools]

The pump will deliver only what the motors demand.

Ted

 

[HPost]

Sounds like you need cross line relief valve that will bolt on to the motor. Set to 120 BAR.

It is the natural fluid dynamics that give only what pressure is needed and no more. That is one of positive points of hydraulic systems. That and the power to weight ratio.

The 200 BAR is the maximum of the pump, not the normal working pressure.

The load sensing is power control that matches the pump flow to the requirement of the motors.

An even better solution would be to install a load sense relief valve and set that to 120 BAR. That way the pump will be controlled by the pressure at the motor and you'll get a better power match between the pump and the motors.

A load sense relief set at 120 BAR would give 120 + margin at the pump (approx 137 to 140 BAR). Once the load sense relief is opened, the pump will reduce its flow.

How you set this up is dependent on the duty profile of the motors and what you want them to do when they get up to max pressure.

 

[NL4L1F3]

Okay thanks for the help. Ill look into it.

 

[3DDave]

If the pump is putting out 53.5 l/minute and the motors aren't free to turn fast enough to clear that volumetric rate, then won't the pressure rise to 200 bar, damaging the motors?

 

[HPost]

No they won't get damaged. At least not if there is a relief at the ports on the motor.

In any case, exceeding the fill limit of a motor will cause the pressure to build in the lines up to the inlet port. The motor itself won't see that pressure.

If the outlet is restricted and the motor pressure rises, that would hurt the motor. In this case, the relief valve would catch the pressure anyway.

For a fixed displacement pump, a cross line relief would be best.

As this system has a load sensing pump, it makes more sense to use a load sense relief valve and to set that just above the maximum working pressure of the motors.

 

[NL4L1F3]

the problem is that i cant set the pressure of the load sense pump. the tractor has 2 connections for the + and - flow only. The speed at which the oil is moving is determined by a handle in the cabin. Thats all i can work with.

Thinking about this, there is a leak connection as well that i can't connect anywhere because it needs low pressure. hmm

 

[HPost]

Does the handle in cabin change the engine speed?

Or

Does the handle adjust a valve that varies the margin and thus changes the pump displacement (flow rate)?

 

[NL4L1F3]

I think you control a valve, because with the handle you can tell a cylinder to go inwards or outwards. That wont be possible with only changing the engine speed. (I think. Not 100% sure)

 

[HPost]

That’s the directional control valve.

There will be a hoses between the pump and that valve. The pressure supply and the load sense line. The return line from the control valve will go back to the tank. You will want to connect the motor case drain to that hose.

Are you going to get another control valve to control the motors or are you planning on using the cylinder control valve?

 

[NL4L1F3]

Would something like this work?

connect the pressure supply of the hydraulic valve to this valve in front of the motor:

https://www.kramp.com/shop-gb/en/411076/510732/224820/CP2001001+Relief+valve+CP200-1+3+8"BSP+ext

(i think this is one of the components you meant?), connect it to the 2 motors (parallel or in series?) and connect it to the return line of the valve.

I plan on using the cylinder control valve. The motors will be controlled from inside the cabin.


EDIT: just saw your new message, changed some text

 

[HPost]

That valve will do 75 litres per minute. That can be used as a relief valve.

It would be advisable to use something smaller as a load sense relief valve.

The load sense relief valve would be connected in the same way, but would be used to limit the pump displacement and so could be smaller and cheaper.

What you are trying to do makes sense and it’s not like you are trying to reinvent the wheel.

Which motors are you looking to use? Displacement wise I mean...

 

[NL4L1F3]

8.2 CC/rev. The load isn't that heavy. What do you mean with the "load sense relief valve"? is "relief valve" the shortened version of it or is it another component?

I appreciate your help a lot, I'm learning a lot

 

[HPost]

Your motors will be doing 3200 rpm

The load sense relief valve is just a relief valve. It limits the pressure in the load sense line and so limits the max pressure of the pump.

The load sense line runs from the control valve to the pump. The load sense relief valve sits in this line and limits the pressure in the load sense line and therefore limits the pressure that pump will generate.

Motor torque will be 120 Newton metres at 100 Bar. Less a little for efficiency.

 

[hydtools]

That cylinder valve will bring the motors to a hard stop when the valve is moved to the off position unless you plumb the motors to run in only one direction.
How much in not much motor load?

Ted

 

[NL4L1F3]

The 2 motors drive a wheel thats hanging freely in the air. Another mechanism feeds the wheels with a round briquette. This briquette will be fired by the wheels. It is the same mechanism used in tennis ball launchers, but enlarged . The load will be very low. I added a screenshot of a cad-drawing in the attachments. This is just a rough drawing to get the point across.

 

[HPost]

To Ted’s point, you are going to need to change the spool in the control valve. Otherwise the inertia in that setup will kill the motors when the spool is returned to neutral.

If your motors will run in one direction only, then you can add a free wheel check valve to allow the motors to run on when the valve is moved to neutral.

 

[NL4L1F3]

the valve isn't just On or off, you can select a middle ground aswell. Would something like that still be required? i ask becouse I've seen machines that only had a motor that was connected to the pressure line and return line with nothing in between and these worked fine aswell.