Parasitic drag of hydraulic motor question

[ParkerFly]

Got an unusual question I'm hoping you all can help with. While in float, does anyone know if a hydraulic motor (char-lynn) would have more parasitic drag on it if the hydraulic pump is turned on or off? Currently I have a setup like this where I put the valve controlling the motor in float and turn the hydraulic pump off (has a clutch on the pulley). I'm considering going to a constant flow pump so I don't have to worry about turning the pump on and off all the time. I don't need the motor creating any more parasitic drag though, it needs to be as free as possible. Would having the pump on/off affect this? Thanks,

Justin

 

[kennyd]

I assume you have a spool valve in between the motor and the pump?

 

[J_J]

How is the hyd motor doing anything if the pump is off. If the valve you are using to control the hyd motor has float, it is used when you turn the hyd motor off to free wheel.

After the motor has stopped, you put the valve lever to neutral.

Float connects all the ports.

Perhaps you should be using a motor spool valve.

Explain what you mean by parasitic drag.

The hyd motor is moving or not moving. You can however use external forces to turn a hyd motor with no pump flow.

http://en.wikipedia.org/wiki/Parasitic_drag

 

[ParkerFly]

Yes I am using a spool valve between the motor and pump. This motor is either working, or I have the valve locked in float letting it free wheel. When its in float it is constantly being turned by the device its attached to until I stop that device and use the motor to reposition it. Then back in float. So while in float, the motor is constantly turning. With the hydraulic pump off, there is no fluid flowing through the system, only the fluid that is left in the lines that may get pumped out as the motor gets turned. If I leave the pump on though there will be plenty of fluid in the lines, and I'm wondering if that makes it harder for the motor to freewheel. A hydraulic guy told me to beware of that once before.

 

[oldnslo]

If the motor is being driven by some external mechanical force you MUST keep both ports of the motor connected. When you are mechanically driving the motor it is acting like a pump and with one of the ports blocked the mechanical driving device will cause pressure to build in one of the motor ports until either:

A) The pressure creates enough load to stall the motor against it's mechanical load.

B) Some thing breaks.. I.e. hose, fitting, drive shaft, etc..

c) Motor cavitates from no inlet flow and slowly self destructs. (A good reason to use a float style spool)

Excess parasitic losses could be caused if the control valve is sized to small to handle full hydraulic pump flow as well as the flow being generated by the motor being mechanically driven. The sum of these two flow rates must pass through the spool valve.

Roy

 

[ParkerFly]

Yes I think I'm on the up and up about needing to keep the ports on the motor connected and will always be leaving my valve in the float position. I'm just trying to determine if it makes any difference whether the pump is pumping fluid through the lines or not while the motor is "floating". While in float it can be spun very fast (well beyond what the motor itself will turn when doing work) and I'm not sure if having fluid pumped through the lines will create the parasitic drag.

 

[J_J]

If you put that same valve back to neutral, the flow to the motor is blocked, however forces can perhaps turn the motor. My Power-trac has hyd motors on each wheel. If I park on a hill, the weight of the machine will cause the hyd motors to act as a pump and push fluid around the hyd circuit. or bypass the motors internally. How much pressure can be generated, I don't know.

They also tell us not to tow the machine very fast or any great distance as the fluid is passing over the relief valves, in a closed loop circuit, and will heat the fluid.

When in neutral, a relief valve across the hyd motor would relieve any pressure build up as the fluid is flowing from the OUT port, to the IN port of the hyd motor.

Just a little curious why you want the hyd motor turning when not in use.

 

[kennyd]

I would change the valve to one made for use with motors, then the work ports are isolated from the IN and OUT ports completey when the valve is in neutral. At that point it will not matter if the pump is on or not.

 

[ParkerFly]

I guess I'll show my ignorance, I didn't know there were different valves available for use with motors. Can you point me in the direction of one of those? And if there is an electric one it would be great too, but mechanical is fine also. Thanks.

 

[kennyd]

I guess I'll show my ignorance, I didn't know there were different valves available for use with motors. Can you point me in the direction of one of those? And if there is an electric one it would be great too, but mechanical is fine also. Thanks.

I can't link one now, but you want one with a "motor spool". They can be had in electric and manual versions. The two work ports are joined together when the valve is in neutral allowing the motor to coast or freewheel. Check the Surplus Center

 

[ParkerFly]

Do you care to explain the difference between a motor spool valve and a regular valve that has a float position? This is a new one for me.
I had my eye on an electric valve earlier that I thought might work for controlling this motor. Here is a link if you don't care to take a look and see what you think:
Northman Fluid Power Hydraulic Directional Control Valve – 26.4 GPM, 4500 PSI, 3-Position, Double Solenoid, Open Center Spool, 12 Volt DC Solenoids, Model# SWH-G03-C3-D12-10 | Power Solenoid | Northern Tool + Equipment
Thanks again,

 

[kennyd]

I have limited wireless access where I am at now, I can link and explain later if you not get an answer before I can get to my desktop-sorry for the delay.

 

[hayden]

I think the answer to your question is Yes, running the pump creates a parasitic load. With your value in float, the motor is circulating fluid in a circle to itself as long as it continues to rotate, and the pump is pumping fluid in a circle to itself as long as the pump is running. Both are parasitic loads, one creating drag on the motor, and the other creating load on whatever is driving the pump. It's not a huge load, but it does take work/energy to pump fluid around in circles.

 

[oldnslo]

Do you care to explain the difference between a motor spool valve and a regular valve that has a float position? This is a new one for me.
I had my eye on an electric valve earlier that I thought might work for controlling this motor. Here is a link if you don't care to take a look and see what you think:
Northman Fluid Power Hydraulic Directional Control Valve 26.4 GPM, 4500 PSI, 3-Position, Double Solenoid, Open Center Spool, 12 Volt DC Solenoids, Model# SWH-G03-C3-D12-10 | Power Solenoid | Northern Tool + Equipment
Thanks again,

Yes this valve will allow the motor to free wheel in the home position. In the home or center position all ports are common just like a "Float" spool.

 

[J_J]

ParkerFly,

You do realize when using a solenoid valve, the hyd motor speed jumps to it's max speed as dictated by the pumps GPM's . You can vary the hyd motor speed by regulating the pumps rpm.

A lever hyd valve can feather and control the speed, fwd or rev if manual operation is needed to vary the motor rpm. If you let it free wheel, there will be more wear and tear on the hyd motor, and perhaps more heat.

There are other ways to control the speed of the motor such as a flow control valve from 1 - 8 GPM's. This is used for one direction only, and has relief.

Surplus Center - 3/8 NPT HYD FLOW CONTROL VALVE W/RELIEF RDRS137-08

There are larger GPM valves available.

 

[SSdoxie]

What do you have this motor connected too that causes it to rotate from the mechanical force? With what I will call a laoder valve with float, when in float the fluid from the pump goes through the open center portion of the valve and back to tank. Both ports on the valve to the motor are open (connected) to each other and also to tank which allows the motor to rotate. To measure pump load on the engine at this point you need to know the pump flow GPM and pressure at the pump. GPM X PSI/1714 = required HP.

 

[ParkerFly]

I think the answer to your question is Yes, running the pump creates a parasitic load. With your value in float, the motor is circulating fluid in a circle to itself as long as it continues to rotate, and the pump is pumping fluid in a circle to itself as long as the pump is running. Both are parasitic loads, one creating drag on the motor, and the other creating load on whatever is driving the pump. It's not a huge load, but it does take work/energy to pump fluid around in circles.

Does running the pump increase the parasitic load on the motor though when it's in float, vs. when the pump is off?

ParkerFly,

You do realize when using a solenoid valve, the hyd motor speed jumps to it's max speed as dictated by the pumps GPM's . You can vary the hyd motor speed by regulating the pumps rpm.

A lever hyd valve can feather and control the speed, fwd or rev if manual operation is needed to vary the motor rpm. If you let it free wheel, there will be more wear and tear on the hyd motor, and perhaps more heat.

Yes, but max speed will be a good thing with my setup. Currently I have lever hyd valve controlling it and it works well, I just have every other hydraulic function on an electric valve and like the simplicity of it. I currently never feather my lever valve, it's always all or nothing. I am able to feather it by varying the RPM of my pump.

What do you have this motor connected too that causes it to rotate from the mechanical force? With what I will call a laoder valve with float, when in float the fluid from the pump goes through the open center portion of the valve and back to tank. Both ports on the valve to the motor are open (connected) to each other and also to tank which allows the motor to rotate. To measure pump load on the engine at this point you need to know the pump flow GPM and pressure at the pump. GPM X PSI/1714 = required HP.

The motor has a sprocket on it and is hooked into the driveline of a large weight. The weight is pulled forward by an axle, and the hydraulic motor is used to pull it back into place. My current pump is 12 GPM @ 2000 RPM - here is a link to the pump I use: https://www.surpluscenter.com/Item.asp?item=9-1737-S
The valve is regulated at 2000 psi. Thanks for all the help and sorry it took me a few days to get back on here and caught up.

 

[SSdoxie]

In answer to question of parasitic load on the hydraulic motor while in float. No, the open center flow from gear pump is not connected to the work ports when in float. Load on the engine at free flow should be less than 1 hp unless it takes more than 150 psi. just to flow the oil. It is rare to see free flowing/non-working pressure over 25 psi. If you do not have an oil cooler in system after the control valve I would suggest you install one. The hydraulic motor, when in float is cycling a small amount of oil through that motor which creates heat. Best to cool that oil down to help seals in the motor last longer.

 

[J_J]

He is using a clutch type hyd pump, and is only working part time to do a specific job, and then he probably shuts off the motor, The hyd motor with the weight attached, is acting as a pump for the time it takes to reel out the weight. The rpm on the hyd motor is probably not that great, and would be dictated by the amount of the weight.

The pump only uses 16 HP to run it.

This setup almost sounds like a system to pull a cover over a dump truck to cover the contenrs.

I am not even sure that parasitic drag has any affect in a short time operation..

 

[DRL]

Sounds more like a tractor pull sled to me. The axle pulls the weight forward during the run and the hydraulics pull it back to the start position.

DRL