question about motor control valve

[marcuswayne]

I built about five years ago a fire wood processor that is run by Hydraulics. The processor has a 30" chainsaw bar with a 404 chain on it. I have a hydraulic spool valve that has an open center that is hooked to a hydraulic cylinder. The cylinder is hooked to the 30" chainsaw bar. This is what moves the 30" bar to cut through the log. The problem that I am having is its hard to control the speed as it cuts through the log. If I change the hydraulic spool valve to a motor control valve will this let me cut slower or faster if I need to?
Thanks for your help
marcus

 

[oldnslo]

You need some form of flow control to regulate the cylinder movement speed. Changing to motor spool will not help

 

[marcuswayne]

I do have a flow control valve on the system. The problem is its hard to control how fast the hydraulic cylinder moves in and out. I would like to be able to open the the spool valve a little for a slower cut if I needed. The spool valve is open or closed, hard to open just a little. If I adjust the flow valve to have less fluid then when I want to make a faster cut I would have to re adjust the flow valve. So a motor control valve wouldn't do that?
thanks for your help

 

[MossRoad]

A motor spool valve lets a motor spin down after you shut off flow to it. Otherwise there'd be a huge shock. It connects the neutral position back to the tank, as I recall. It doesn't affect speed as I understand it.

Speed is controlled with a flow valve.

At least I think that's how it all works. Maybe someone else will correct me if I'm wrong.

 

[MossRoad]

Couldn't you just use a valve like what's on a front end loader that raises and lowers the arms?

On my loader, the more I push it the faster it raises. The more I pull it, the faster it lowers. If I let off of it, it stays where it's at.

 

[oldnslo]

If you have the knowledge and skill a electrical proportion valve will do what you want but for precise control of low flows they are not inexpensive. For even better control You can “close the loop electronically” If electrical control is connected to a pressure transducer to indicate saw motor pressure to control cylinder speed - valve position.

Is your flow control pressure compensated or simple flow control?

Pressure compensated might provide a little more consistent speed but again will not change speed unless you adjust it.

 

[marcuswayne]

A motor spool valve lets a motor spin down after you shut off flow to it. Otherwise there'd be a huge shock. It connects the neutral position back to the tank, as I recall. It doesn't affect speed as I understand it.

Speed is controlled with a flow valve.

At least I think that's how it all works. Maybe someone else will correct me if I'm wrong.

thank you MossRoad
i have never used a motor spool valve in all the things I have built. That makes sense that the valve would let the motor spin down after it's shut off.

 

[marcuswayne]

If you have the knowledge and skill a electrical proportion valve will do what you want but for precise control of low flows they are not inexpensive. For even better control You can “close the loop electronically” If electrical control is connected to a pressure transducer to indicate saw motor pressure to control cylinder speed - valve position.

Is your flow control pressure compensated or simple flow control?

Pressure compensated might provide a little more consistent speed but again will not change speed unless you adjust it

 

[mrmikey]

A motor spool, other than allowing the motor to freewheel when returned to neutral sometimes has either a tapered land rather than an abrupt square edge or else cuts around the circumference of the land to allow easier feathering of the flow.
I've ground tapers on a spool before when I've been in a pinch and it's worked but it was more luck than skill as there's a good chance of warping the spool
Not good examples but all I could find:

 

[marcuswayne]

If you have the knowledge and skill a electrical proportion valve will do what you want but for precise control of low flows they are not inexpensive. For even better control You can “close the loop electronically” If electrical control is connected to a pressure transducer to indicate saw motor pressure to control cylinder speed - valve position.

Is your flow control pressure compensated or simple flow control?

Pressure compensated might provide a little more consistent speed but again will not change speed unless you adjust it.

the flow control is an inline pressure compensated valve.

 

[marcuswayne]

Couldn't you just use a valve like what's on a front end loader that raises and lowers the arms?

On my loader, the more I push it the faster it raises. The more I pull it, the faster it lowers. If I let off of it, it stays where it's at.

I think that is going to be my next thing to try. The valve that I am using came off a riding lawn mower ( small valve ). The valve is open or closed. If I use a lager valve that might work, giving me more control over the flow. Thank you

 

[MTGreen]

Did you use an oversized valve in terms of flow? My limited understanding is that if the valve is oversized it will be harder to make fine adjustments.

I also asked on TBN one time if there was a difference in feathering/fine adjustment ability with cheap/chi-com valves and quality high dollar valves and never got a really satisfactory answer. I suspect that there is a difference

 

[oldnslo]

MTgreen is correct that over size valve makes fine movements far more difficult. Typically but not always more expensive valves will have better metering characteristics for fine control and some will have built in compensator to make the valve spool pressure compensated for even more consistent flow control with varying inlet and work port pressure.

Marcus,
any idea what flow rate you are trying to control to that feed cylinder? I suspect probably less than 1 GPM for cutting. Am I close?

 

[marcuswayne]

Did you use an oversized valve in terms of flow? My limited understanding is that if the valve is oversized it will be harder to make fine adjustments.

I also asked on TBN one time if there was a difference in feathering/fine adjustment ability with cheap/chi-com valves and quality high dollar valves and never got a really satisfactory answer. I suspect that there is a difference

The valve that I used is a small valve used on like a 20hp riding lawn mower.

 

[marcuswayne]

MTgreen is correct that over size valve makes fine movements far more difficult. Typically but not always more expensive valves will have better metering characteristics for fine control and some will have built in compensator to make the valve spool pressure compensated for even more consistent flow control with varying inlet and work port pressure.

Marcus,
any idea what flow rate you are trying to control to that feed cylinder? I suspect probably less than 1 GPM for cutting. Am I close?

Not sure of the flow rate, it also is hooked to other valves to run like the log hold down and the hydraulic motor to move the logs forward. So Im sure the feed rate is much higher.

 

[rScotty]

instead of trying to deal with the hydraulic flow rate directly, maybe it would be easier to put speed control onto whatever is driving your hydraulic pump. That has the advantage of keeping the pressure more constant when changing the flow rate.

 

[marcuswayne]

instead of trying to deal with the hydraulic flow rate directly, maybe it would be easier to put speed control onto whatever is driving your hydraulic pump. That has the advantage of keeping the pressure more constant when changing the flow rate.

The problem with that is there are times when I would like to cut faster, like when I am cutting soft wood. When cutting hard wood I need to give the cutter bar more time to cut.
The way thing are right now is it works great until I cut into something really hard and need to give the chain more time to cut.

 

[LouNY]

So it sounds like all you need to do is adjust the rate of the cylinder that is moving your cutterbar.
Something like this would allow you to regulate the cylinder slower in one direction while retaining full speed in the other. This valve allows flow to be restricted one way but allows full flow back the other way.

 

[marcuswayne]

So it sounds like all you need to do is adjust the rate of the cylinder that is moving your cutterbar.
Something like this would allow you to regulate the cylinder slower in one direction while retaining full speed in the other. This valve allows flow to be restricted one way but allows full flow back the other way.
View attachment 858290

I think that you are right. it will labor the hydraulic pump but I can adjust the pressure relief valve. Thanks

 

[oldnslo]

Not sure of the flow rate, it also is hooked to other valves to run like the log hold down and the hydraulic motor to move the logs forward. So Im sure the feed rate is much higher.

Marcus
Are you manually operating the controls for saw feed or is it electrically operated? I was assuming electric but now not sure.

If manual then a good metering valve sized properly could help.

To determine required flow you can measure the cylinder movement in inches per second and with known cylinder size calculate the required flow rate.

Formula is: flow = cylinder velocity times cylinder area