Hydraulic toplink advice

[Bennevis]

I have a remote hydraulic set up for my 851 & I am thinking a hydraulic toplink would be a good idea. Do you guys have any suggestions on specific toplink brands/resources? I know there is a basic range for the hydraulic toplink - just like a manual one, but I adjust my manual toplink to different lengths depending on the implement (so, I'm kinda confused on measuring the toplink, since it's adjustable & not specific to my tractor). Any help is greatly appreciated!

 

[Jim.ME]

I have a remote hydraulic set up for my 851 & I am thinking a hydraulic toplink would be a good idea. Do you guys have any suggestions on specific toplink brands/resources? I know there is a basic range for the hydraulic toplink - just like a manual one, but I adjust my manual toplink to different lengths depending on the implement (so, I'm kinda confused on measuring the toplink, since it's adjustable & not specific to my tractor). Any help is greatly appreciated!

You are looking for cylinder range. If you know the lengths you adjust your manual top link to, you need a top link with a retracted length shorter than your shortest adjustment and extended length longer than your longest adjustment length. You just measure center of your manual top link pin hole to the center of the other pin hole at your shortest and longest adjustments and get a cylinder that covers that range, pin hole to pin hole, retracted and extended. You use the remote to adjust the cylinder length within that cylinder range.

 

[Texasmark]

I thought about a top link once but realized that hydraulic fluid expands (like most fluids) with an increase in temp. That means that you start out with one length and over time it changes with the fluid temp changes. I decided that the manual, screw type would be the better decision as you set it and forget it.

You asked I replied.

 

[Ozlander]

I've got hydraulic top links on both of my tractors. Best addition I could make.

 

[Jim.ME]

I thought about a top link once but realized that hydraulic fluid expands (like most fluids) with an increase in temp. That means that you start out with one length and over time it changes with the fluid temp changes. I decided that the manual, screw type would be the better decision as you set it and forget it.

You asked I replied.

Each of us can choose which we want to use. Your implements must all be exactly the same geometry at the hitch points, if you never have to adjust your top link.

Expansion will be minimal. The oil will expand on both sides of the piston which will minimize movement of the rod. Your manual screw top link expands and contracts as well. Just saying I don't see expansion being a problem.

 

[Fritz Maurer]

I don't understand why oil trapped in the cylinder would get hot.

 

[TheOldHokie]

I have a remote hydraulic set up for my 851 & I am thinking a hydraulic toplink would be a good idea. Do you guys have any suggestions on specific toplink brands/resources? I know there is a basic range for the hydraulic toplink - just like a manual one, but I adjust my manual toplink to different lengths depending on the implement (so, I'm kinda confused on measuring the toplink, since it's adjustable & not specific to my tractor). Any help is greatly appreciated!

Measure the minimum and maximum length of your manual toplink and buy a hydraulic link that matches

I suggest you get one with a check valve to prevent cylinder drift when in use.

TOH

 

[TheOldHokie]

I thought about a top link once but realized that hydraulic fluid expands (like most fluids) with an increase in temp. That means that you start out with one length and over time it changes with the fluid temp changes. I decided that the manual, screw type would be the better decision as you set it and forget it.

You asked I replied.

Hydraulic oil is also incompressible. With both ports blocked the cylinder is hydraulically locked and cylinder pressure may go up or down with temperature but it cannot change length.

TOH

 

[Sean in PA]

I don't understand why oil trapped in the cylinder would get hot.

The implement bouncing up and down when you transport an implement causes the hydraulic toplink to compress and extend slightly repeatedly, and that causes pressure. Fluids under pressure in a sealed environment heat up.

 

[TheOldHokie]

The implement bouncing up and down when you transport an implement causes the hydraulic toplink to compress and extend slightly repeatedly, and that causes pressure. Fluids under pressure in a sealed environment heat up.

The oil cannot compress or expand. Its the pressure spikes that generate heat. Not to mention the sun.

TOH

 

[Jim.ME]

I don't understand why oil trapped in the cylinder would get hot.

Have you ever had trouble connecting quick couplers to a tractor after an implement was unhooked in cooler conditions? That is caused by the oil warmed by the sun and ambient temperature increase, expanding the cylinder and oil while setting. A metal top link will expand under the same conditions. The fact is the expansion will only be a few thousands of an inch. I don't think a top link adjustment is precision enough that the change to an implement setting will be noticed.

If a cylinder is stroking a good bit and a tractor is warm the warm oil will transfer into the cylinder as it cycles. I would not expect it to be an issue with a top link.

 

[TheOldHokie]

Have you ever had trouble connecting quick couplers to a tractor after an implement was unhooked in cooler conditions? That is caused by the oil warmed by the sun and ambient temperature increase, expanding the cylinder and oil while setting. A metal top link will expand under the same conditions. The fact is the expansion will only be a few thousands of an inch. I don't think a top link adjustment is precision enough that the change to an implement setting will be noticed.

If a cylinder is stroking a good bit and a tractor is warm the warm oil will transfer into the cylinder as it cycles. I would not expect it to be an issue with a top link.

One more time.

The cylinder is sealed and the rod is hydraulically locked. It cannot move.

For all practical purposes here the oil is incompressible and cannot expand. The added heat energy causes the pressure inside the cylinder to increase.

TOH

 

[Jim.ME]

One more time.

The cylinder is sealed and the rod is hydraulically locked. It cannot move.

The oil is incompressible and cannot expand but the added heat causes the pressure inside the cylinder to increase.

TOH

I agree oil for practical purposes does not compress. Sorry I was not clear in saying that the metal cylinder dimensions grow, so OAL of the rod will grow a few thousandths of an inch. Some of what both of us are saying can be just different ways of saying the same thing but if you research oil expansion, I believe you will find it does expand (and contract when cooled), and oil can be compressed under some conditions.

The metal cylinder will expand as it warms, and it dimensions will increase. Cool the cylinder and it shrinks. The oil in it will react similarly as well. It may not expand as much as it would if it was in an open container, but it will expand and that expansion or contraction of the oil causes the pressure to increase or decrease in the cylinder. If the oil was not trying to expand as it warms, the pressure would drop as the metal cylinder warmed and grew, wouldn't it.

If you have a locked cylinder with a relief valve ported directly in the cylinder. The cylinder is completely filled with oil and pressurized to the relief valve pressure and the inlet and outlet ports are closed. Then you heat the cylinder, we agree the pressure will increase. When the relief valve opens due to excess pressure above its setting, I believe oil will come out, would you agree on that? If the oil has not expanded, will the cylinder have an air pocket and no longer be full? It would seem that there would be a void inside the cylinder if the oil had not expanded.

This is basically what is seen when the cylinder on an implement being connected using remote couplers. Unhook it in cold weather (32 degrees ambient) then go to hook up in warm sunny weather (80 degrees ambient) and, if there are no leaks, generally you have to release oil from the coupling before it can be connected, at least in this area you have to. The pressure in the coupling increased due to expansion of the fluid in that system increasing the pressure. Unhook the hoses at 90 degrees ambient temp and hook up at 32 degrees is not a problem, contraction lowers the pressure in the system. If expansion of the oil/fluid due to warming is not causing the pressure increase, what is? Heat causes expansion, expansion increases the pressure.

Is pressure or expansion/contraction of a fluid the reason a closed captive cooling system works? Why does the radiator stay full if the fluid has not expanded when some has gone to the catch tank?

Interesting discussion, but beyond the original question. We both have suggested he get a hydraulic unit based on the length adjustment range of his manual link. And I agree it should be one with the check/holding valve do prevent unwanted drifting.

 

[TheOldHokie]

I agree oil for practical purposes does not compress. Sorry I was not clear in saying that the metal cylinder dimensions grow, so OAL of the rod will grow a few thousandths of an inch. Some of what both of us are saying can be just different ways of saying the same thing but if you research oil expansion, I believe you will find it does expand (and contract when cooled), and oil can be compressed under some conditions.

The metal cylinder will expand as it warms, and it dimensions will increase. Cool the cylinder and it shrinks. The oil in it will react similarly as well. It may not expand as much as it would if it was in an open container, but it will expand and that expansion or contraction of the oil causes the pressure to increase or decrease in the cylinder. If the oil was not trying to expand as it warms, the pressure would drop as the metal cylinder warmed and grew, wouldn't it.

If you have a locked cylinder with a relief valve ported directly in the cylinder. The cylinder is completely filled with oil and pressurized to the relief valve pressure and the inlet and outlet ports are closed. Then you heat the cylinder, we agree the pressure will increase. When the relief valve opens due to excess pressure above its setting, I believe oil will come out, would you agree on that? If the oil has not expanded, will the cylinder have an air pocket and no longer be full? It would seem that there would be a void inside the cylinder if the oil had not expanded.

This is basically what is seen when the cylinder on an implement being connected using remote couplers. Unhook it in cold weather (32 degrees ambient) then go to hook up in warm sunny weather (80 degrees ambient) and, if there are no leaks, generally you have to release oil from the coupling before it can be connected, at least in this area you have to. The pressure in the coupling increased due to expansion of the fluid in that system increasing the pressure. Unhook the hoses at 90 degrees ambient temp and hook up at 32 degrees is not a problem, contraction lowers the pressure in the system. If expansion of the oil/fluid due to warming is not causing the pressure increase, what is? Heat causes expansion, expansion increases the pressure.

Is pressure or expansion/contraction of a fluid the reason a closed captive cooling system works? Why does the radiator stay full if the fluid has not expanded when some has gone to the catch tank?

Interesting discussion, but beyond the original question. We both have suggested he get a hydraulic unit based on the length adjustment range of his manual link. And I agree it should be one with the check/holding valve do prevent unwanted drifting.

Yes, things have wandered into the weeds a bit. But its importabt to dispel myths.

If you want to understand hydrailic cylinders you need to understand the underlying physics. Your analysis is throwing in a lot of elements that obscure that underlying physics. Things like the rod increasing in length are totally irelevant and thermal expansion of cylinder and fluid is so insignificant it can be ignored.

For a basic hydraulic cylinder of this type the number one and dominant factor in the hydrostatic pressure increase is the increase in molecular kinetic energy from the heat. And unlike heating a gas the oil cannot be compressed so there is no stored potential energy that will launch a stream of fluid out that relief valve. A tiny dribble almost instantly drops fluid pressure below cracking pressure and the relief closes..Try it and see.

TOH

 

[Jim.ME]

I did not say there would be a stream of fluid out the relief valve, only that it opens and oil comes out. I know the pressure drop as soon as it opens and a bit of oil escapes. I have used oil and pumps to tear down large air cylinders with stuck gland heads for that reason, as soon as oil can get by the gland the pressure is gone, no explosion and flying parts as will happen when air is used.

I got into the expansion in reply to Texasmark's comment about the hydraulic link changing length due to the fluid expanding and was trying to point out the mechanical top link expands as well and that I didn't see expansion as a problem with either.

While considered non or in-compressible for practical purposes, the fact is Oil/fluids can be compressed under some high-pressure conditions. Also, Oil/fluids will expand when heated and contract when cooled. To me, the pressure increasing when heated indicates the fluid is trying to expand and is expanding as evidenced if it escapes from the relief. How else do you explain the hook up issues with remote cylinders I mentioned and captive cooling systems in layman's terms?

With respect it may just be that we are wording things somewhat differently and not that far apart.

 

[TheOldHokie]

I did not say there would be a stream of fluid out the relief valve, only that it opens and oil comes out. I know the pressure drop as soon as it opens and a bit of oil escapes. I have used oil and pumps to tear down large air cylinders with stuck gland heads for that reason, as soon as oil can get by the gland the pressure is gone, no explosion and flying parts as will happen when air is used.

I got into the expansion in reply to Texasmark's comment about the hydraulic link changing length due to the fluid expanding and was trying to point out the mechanical top link expands as well and that I didn't see expansion as a problem with either.

While considered non or in-compressible for practical purposes, the fact is Oil/fluids can be compressed under some high-pressure conditions. Also, Oil/fluids will expand when heated and contract when cooled.

Almost but with one caveat. Liquids will expand when heated but not when contained in a filled and sealed pressure vessel. Its an important distinction and the reason you dont get that "explosion" if the vessel ruptures.

TOH

 

[Sean in PA]

The oil cannot compress or expand. Its the pressure spikes that generate heat. Not to mention the sun.

TOH

OK, it causes the top link to "try to compress" which causes the heat.

 

[TheOldHokie]

OK, it causes the top link to "try to compress" which ca9uses the heat.

Yes.

The point I am trying to make here is discussions of internal cylinder pressure is a red herring. Jim came close but did not say it quite this explicitly

As long as there is no external fluid leakage a hydraulic top link behaves just like a steel rod.

Thats why the double check valves are used. Without them you will generally see leakage and a very noticeable amount of cylinder drift.

TOH

 

[Jim.ME]

Yes.

The point I am trying to make here is discussions of internal cylinder pressure is a red herring. Jim came close but did not say it quite this explicitly

As long as there is no external fluid leakage a hydraulic top link behaves just like a steel rod.

Thats why the double check valves are used. Without them you will generally see leakage and a very noticeable amount of cylinder drift.

TOH

Agreed, that was the point I was trying to make in regard to Texasmark's comment in his post (#3) about the hydraulic top link's length changing and his manual one being "set it and forget it"; however poorly I worded it.

.

 

[showcrop]

I have a remote hydraulic set up for my 851 & I am thinking a hydraulic toplink would be a good idea. Do you guys have any suggestions on specific toplink brands/resources? I know there is a basic range for the hydraulic toplink - just like a manual one, but I adjust my manual toplink to different lengths depending on the implement (so, I'm kinda confused on measuring the toplink, since it's adjustable & not specific to my tractor). Any help is greatly appreciated!

Top links are nearly always sized not by the length but by category. 0; 1; 2; 3, etc. they are all adjusted for different implements. Your 851 takes a cat 1. Your hyd. unit needs to be sized the same way.