single action cylinder question(s)

[blenderbender]

I picked up a Chinese sickle bar mower that has a single action hydraulic cylinder, power up/gravity down. My Kubota tractor has a single set of rear remotes on a dual action control. I don't understand hydraulics nearly well enough, but I'm guessing this is a problem in terms of using this single action cylinder and I don't have a clue what my options might be other than swapping out for a dual acting cylinder. Any thoughts appreciated!

 

[TheOldHokie]

I picked up a Chinese sickle bar mower that has a single action hydraulic cylinder, power up/gravity down. My Kubota tractor has a single set of rear remotes on a dual action control. I don't understand hydraulics nearly well enough, but I'm guessing this is a problem in terms of using this single action cylinder and I don't have a clue what my options might be other than swapping out for a dual acting cylinder. Any thoughts appreciated!

You can use one port as is (not recommended) or connect the unused port to a tank return (recommended).

Dan

 

[McMXi]

You can use one port as is (not recommended)

The Land Pride RC3712 12ft folding cutter came set up that way for all three cylinders. One hydraulic hose for the two wings, and one for the center deck. No problems to report so far.

 

[TheOldHokie]

The Land Pride RC3712 12ft folding cutter came set up that way for all three cylinders. One hydraulic hose for the two wings, and one for the center deck. No problems to report so far.

View attachment 149146

View attachment 149143

View attachment 149144

View attachment 149145

You are deadheading the pump every time you retract the SA cylinders. Like I said it works but its not the best way to plumb the valve.

 

[McMXi]

You are deadheading the pump every time you retract the SA cylinders. Like I said it works but its not the best way to plumb the valve.

The wings don't get lifted much unless I'm putting the tractor and cutter on the trailer, but the center deck is raised regularly when cutting, but not necessarily to the limit of the lifting cylinder. When fully raising the wings or the center deck, the pump is dead headed for less than a second. I'd be curious to see data comparing the service life of an hydraulic pump that gets dead headed for a less than a second a few thousands times vs. one that never gets dead headed.

But perhaps it wouldn't be hard to make up a couple of hoses to run from the other fittings back to the tank. Given the cost of the folding cutter, I would hope that Kubota/Land Pride aren't knowingly setting customers up for problems down the road.

 

[TheOldHokie]

The wings don't get lifted much unless I'm putting the tractor and cutter on the trailer, but the center deck is raised regularly when cutting, but not necessarily to the limit of the lifting cylinder. When fully raising the wings or the center deck, the pump is dead headed for less than a second. I'd be curious to see data comparing the service life of an hydraulic pump that gets dead headed for a less than a second a few thousands times vs. one that never gets dead headed.

Have it your way.

Dan

 

[McMXi]

Have it your way.

Dan

I intend to.

And for those not familiar with the concept of dead heading a pump, here's a brief explanation.

What is dead-heading a pump?
A dead-head is caused when a centrifugal pump operates with no flow through the pump due to a closed discharge valve or blockage in the line. The pump is forced to circulate the pumped medium, causing the temperature to continually rise. As the fluid churns inside the pump it heats into a vapor. Once a vapor is created, any bushings or mechanical seals in the pump heat to the point that they begin to crack, shatter, score or compromise the elastomers - killing the pump.

Effects of Dead Heading
1. Increased Pressure: When a pump is dead headed, pressure can build up to dangerous levels, risking damage to the pump and piping.
2. Overheating: Continuous operation against a closed discharge can cause the pump to overheat, leading to seal failure and other mechanical issues.
3. Cavitation: In some cases, the drop in pressure within the pump can lead to cavitation, which can cause severe damage to the pump components.
4. Reduced Efficiency: Operating under dead head conditions is inefficient and can lead to increased energy consumption and operational costs.

So from a practical point of view, is a one second or less dead head event likely to lead to any of the issues described?

 

[TheOldHokie]

I intend to.

And for those not familiar with the concept of dead heading a pump, here's a brief explanation.

What is dead-heading a pump?
A dead-head is caused when a centrifugal pump operates with no flow through the pump due to a closed discharge valve or blockage in the line. The pump is forced to circulate the pumped medium, causing the temperature to continually rise. As the fluid churns inside the pump it heats into a vapor. Once a vapor is created, any bushings or mechanical seals in the pump heat to the point that they begin to crack, shatter, score or compromise the elastomers - killing the pump.

You are also overpressuring the T port on the valve by about 2000 PSI. Over time you can and probably will blow the spool seals. Happens to the BH backhoe valves on a regular basis. But have it your way.

Dan

 

[McMXi]

You are also overpressuring the T port on the valve by about 2000 PSI. Over time you can and probably will blow the spool seals. Happens to the BH backhoe valves on a regular basis. But have it your way.

Dan

OK ... this is a more compelling reason to add a hose(s) to return oil to the tank. For the record, I ordered and received new spool seals for the Faster connectors to address a leak, but one of them was leaking long before I bought the RC3712, and the folding cutter is the first implement I've owned with single acting cylinders.

So additional hoses might be added to spring/summer project list.

 

[North Idaho Wolfman]

OK ... this is a more compelling reason to add a hose(s) to return oil to the tank. For the record, I ordered and received new spool seals for the Faster connectors to address a leak, but one of them was leaking long before I bought the RC3712, and the folding cutter is the first implement I've owned with single acting cylinders.

So additional hoses might be added to spring/summer project list.

I looked it up and as I thought there does appear to be a provision for bypass for a single action cylinder.
I'll see if I can get confirmation to that effect.

 

[Kennyd4110]

You are deadheading the pump every time you retract the SA cylinders.

No, the PRV (pressure relief valve) prevents that from happening.

 

[RCW]

EDIT: I think I answered my own questions after some thought.

I'll leave the rest of my post for what it's worth, but I don't think it's applicable to the question at hand.

I can't think of anything we had with D-A cylinders. I don't think the MF had two ports on its remote either. I believe that was set up for just S-A cylinders if my memory serves.

Just for my own information/recollection.

I've been off the farm for several decades; wasn't it common to use one side of a remote for a single-acting cylinder years ago? Or am I just not recalling correctly (entirely possible)?

We had a MF Super 90 that (I think) we connected that way for our Crimper's SA lift, but other implements used both "sides".

Was that a difference between open-center and closed-center, or were we just lucky we didn't have problems? Or is it likely that 1966 MF didn't have a remote with two connections?

My old Minneapolis Moline is only equipped for single action, both loader and rear remote.

Again, my memory may be off. One of my jobs as a youngster was hooking stuff up while my grandfather or father backed up to them. By 6-7 years of age, my job was backing up, then getting down and hooking implements up by myself...

 

[TheOldHokie]

EDIT: I think I answered my own questions after some thought.

I'll leave the rest of my post for what it's worth, but I don't think it's applicable to the question at hand.

I can't think of anything we had with D-A cylinders. I don't think the MF had two ports on its remote either. I believe that was set up for just S-A cylinders if my memory serves.

Just for my own information/recollection.

I've been off the farm for several decades; wasn't it common to use one side of a remote for a single-acting cylinder years ago? Or am I just not recalling correctly (entirely possible)?

We had a MF Super 90 that (I think) we connected that way for our Crimper's SA lift, but other implements used both "sides".

Was that a difference between open-center and closed-center, or were we just lucky we didn't have problems? Or is it likely that 1966 MF didn't have a remote with two connections?

My old Minneapolis Moline is only equipped for single action, both loader and rear remote.

Again, my memory may be off. One of my jobs as a youngster was hooking stuff up while my grandfather or father backed up to them. By 6-7 years of age, my job was backing up, then getting down and hooking implements up by myself...

Fords of that vintage used valves that could be switched between single and double acting. Nothing more than a selector on the valve body that connected one side to tank. Thats still the case on many agricultural tractors today.

Dan

 

[TheOldHokie]

No, the PRV (pressure relief valve) prevents that from happening.

That is semantics. If you prefer the pump is "unloading" across the PRV at max system pressure. Thats a totally unnecesary and undesirable situation you can easily avoid with a simple tank return loop.

Dan

 

[Kennyd4110]

That is semantics. If you prefer the pump is "unloading" across the PRV at max system pressure. Thats a totally unnecesary and undesirable situation you can easily avoid with a simple tank return loop.

Dan

It happens just about EVERYTIME one uses their loader.

 

[TheOldHokie]

It happens just about EVERYTIME one uses their loader.

Like I said up front - it works but its not the best way to do it. Theres a reason real AG tractors with open center hydraulics have DA/SA switchable valves.

I stand by my recommendation - provide a tank return for the unused work port. Feel free to ignore that recommendation.

Dan