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USN
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Discussion Starter · #1 ·
My GT has hydrostatic drive with hydraulic lift using hydraulic pressure from the drive unit. If the hydrostatic drive operates at 500# pressure, does the lifting ram also have 500# thrust? If this is correct, it will help me determine the ram thrust I need to replace the hydraulic lift on the front of my GT to operate the front bucket/scoop.

Thanks
 

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My GT has hydrostatic drive with hydraulic lift using hydraulic pressure from the drive unit. If the hydrostatic drive operates at 500# pressure, does the lifting ram also have 500# thrust? If this is correct, it will help me determine the ram thrust I need to replace the hydraulic lift on the front of my GT to operate the front bucket/scoop.

Thanks
If you have 500 PSI it will be 500 pound per inch of cylinder. A 2" cylinder is 3.14" of area = 1570 lbs. less resistance.
 

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USN
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Discussion Starter · #3 ·
If you have 500 PSI it will be 500 pound per inch of cylinder. A 2" cylinder is 3.14" of area = 1570 lbs. less resistance.
Thanks. That makes sense. Of course, I don't know the actual pressure of the fluid, but I assume that 500psi would be a good guess. My manual says 500_50, which make no sense to me. Is it 500psi or 50psi? I suspect it is a typo, but don't know which is correct.
 

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Blacksmith
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Remember that the 500 psi is at a very low flow rate about 1.5 gpm. For a larger diameter cylinder like 2" it will take a long time to move it. I added another pump to run my FEL with 2" cylinders. The pump is over 4 gpm.
 

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USN
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Discussion Starter · #6 ·
......but read that as 500# on your high pressure side, and 50# on your return or low pressure. Is this correct?

Hadn't thought of that. Perhaps that is correct????

Remember that the 500 psi is at a very low flow rate about 1.5 gpm. For a larger diameter cylinder like 2" it will take a long time to move it. I added another pump to run my FEL with 2" cylinders. The pump is over 4 gpm.
I just measured my existing cylinder. It has a 1-5/8" bore and a 4.5" stroke. I was actually considering replacing it with a larger diameter cylinder......say 2". Does an added 3/8" diameter make that much difference with that low flow rate? At 500psi this cylinder has a thrust of just over 1000#. A 2" bore would increase that thrust to just over 1500#.......albeit at a slower rate. That adds 4.8 ci or about 50% volume, so I'd guess if it takes 2 seconds to raise the bucket it would add another second with the larger cylinder......if I did my math correctly. I did round things off some. so this is approximate.

Am I thinking correctly?
 

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Thanks. That makes sense. Of course, I don't know the actual pressure of the fluid, but I assume that 500psi would be a good guess. My manual says 500_50, which make no sense to me. Is it 500psi or 50psi? I suspect it is a typo, but don't know which is correct.
The charge pump supplies the drive pump with make-up fluid, and may or may not, depending on the options available for the tractor, also supply the implement lift hydraulics.

If there is no implement hydraulic circuit, the charge relief will be in the area of 50-110 psi, depending on the manufacturer. With the implement circuit, a different relief valve is used, the original charge relief is plugged off, and the 500-750 implement relief covers both jobs. The individual tractor manufacturers can sometimes spec the relief settings that they want, therefore the ranges that I have mentioned. 500/50 is actually about the lowest that you will find for the 2 relief pressures.

I just measured my existing cylinder. It has a 1-5/8" bore and a 4.5" stroke. I was actually considering replacing it with a larger diameter cylinder......say 2". Does an added 3/8" diameter make that much difference with that low flow rate? At 500psi this cylinder has a thrust of just over 1000#. A 2" bore would increase that thrust to just over 1500#.......albeit at a slower rate. That adds 4.8 ci or about 50% volume, so I'd guess if it takes 2 seconds to raise the bucket it would add another second with the larger cylinder......if I did my math correctly. I did round things off some. so this is approximate.

Am I thinking correctly?
Your math is correct. Another variable involved is engine rpm. The positive displacement charge pump is driven by the engine and varying the engine speed will also vary the flow rate. A charge pump that will flow 1.5 gpm at full throttle (3600 rpm) will flow 1 gpm at half throttle (2400 rpm).

Pressure defines how much work can be done and flow defines how fast work can be done.

1 Gallon = 231 cubic inches

Don't forget that the rod takes up volume on the return stroke, so it's a little quicker. Full stroke in 2 - 5 seconds is a comfortable time with raising or lowering implements. Too fast is not fun and too slow is boring. Most of the time it takes less than full stroke to lower the implement, but we usually tend to hold the lever long enough for full stroke when dropping it. Most implement lifts have a mechanical float function built into the linkage. For precise raising or lowering a bucket of any description, speed is not your friend.
 

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USN
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Discussion Starter · #8 ·
Don't forget that the rod takes up volume on the return stroke, so it's a little quicker.
I believe I'm getting it. You mentioned the rod (ram) taking up volume on the return stroke. That rod would also take up area from the piston and, in effect, make the return stroke less powerful. Correct? The bigger diameter of the ram, the less power the return stroke would have??? If that's true, lifting, as in a bucket, should be on the push stroke rather than the pull stroke.

My tractor is lifting on the push stroke on the front, but on the pull stroke on the back.

Lots to think about, but it coming together up stairs.
 

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I believe I'm getting it. You mentioned the rod (ram) taking up volume on the return stroke. That rod would also take up area from the piston and, in effect, make the return stroke less powerful. Correct? The bigger diameter of the ram, the less power the return stroke would have??? If that's true, lifting, as in a bucket, should be on the push stroke rather than the pull stroke.

My tractor is lifting on the push stroke on the front, but on the pull stroke on the back.

Lots to think about, but it coming together up stairs.
Correct! The piston has full area on the push stroke for the pressure to act against. On the return stroke, the rod takes some of that area away from the gross piston area leaving fewer square inches to work with.

Depending on the leverage involved, you should be okay either pushing or pulling. It would take a large rod to make a big difference.

Here's a primer for you.

http://www.edgeroamer.com/sweethaven/mechanics/hydraulics01/
 

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USN
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Discussion Starter · #11 ·
Trying to expand my horizons a bit. It seems another way to accomplish my task would be to disconnect the hydraulic lines (from the hydrostatic unit) to and from the control valve, plug them and add a pump that has a bit more pressure.

I have a belt driven PTO that is unused and I believe it could be used to drive an auxilary pump...perhaps a power steering pump. I've been reading past threads about using PS pumps and it seems feasible. The pump could be mounted under the tractor where a belly mounted mower would be (if it had one) and driven by the same belt system that drives a belly mounted mower. That puts it close to the control valve. My hoses already have been replaced with 2000 psi hoses and the cylinder has been rebuilt.

One question that comes to mind is.....can the PS pump be mounted facing downward with the sheave running horizontally? I've noticed the PS pump on my old Dodge Van has a remote reservoir, so a similar pump would be ideal.

The hydrostatic unit that powers my lift system now, has a built-in pressure relief. Is there a pressure relief built-in to the normal PS pump?

Is there any other reason why this would not be workable?
 

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Jack, a real good way to cook your hydro is to plug off the lines. If you don't want to make use of the circuit, route a single line between the 2 ports.

What GT do you have? Which hydro? Most hydros will put out 1 - 3 gpm for the implement lift hydraulics. Most automotive power steering pumps will flow 1.9 - 2.4 gpm. Not much gain involved for a lot of expensive and/or time consuming work. They do have an internal flow control and relief valve set at 1250 - 1450 psi for GM pumps and I hear that Dodge is now using the same pump.

Hydraulic pumps don't care how they are oriented, sideways, backwards, upside down or at an angle, as long as the input shaft turns the right direction and they get a sufficient supply of oil, they're happy.

Unless you're planning on using a much larger cylinder than the one you mentioned, there isn't any reason to add a pump. Stick with what you have. It's sized correctly for both volume and pressure.

If you plan on a hydraulic dump cart or log splitter, that's different. Build a complete system to do either of those jobs, but keep the implement lift system as it is, even with the new cylinder.
 

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USN
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Discussion Starter · #13 ·
Jack, a real good way to cook your hydro is to plug off the lines. If you don't want to make use of the circuit, route a single line between the 2 ports.

What GT do you have? Which hydro? Most hydros will put out 1 - 3 gpm for the implement lift hydraulics. Most automotive power steering pumps will flow 1.9 - 2.4 gpm. Not much gain involved for a lot of expensive and/or time consuming work. They do have an internal flow control and relief valve set at 1250 - 1450 psi for GM pumps and I hear that Dodge is now using the same pump.

Hydraulic pumps don't care how they are oriented, sideways, backwards, upside down or at an angle, as long as the input shaft turns the right direction and they get a sufficient supply of oil, they're happy.

Unless you're planning on using a much larger cylinder than the one you mentioned, there isn't any reason to add a pump. Stick with what you have. It's sized correctly for both volume and pressure.

If you plan on a hydraulic dump cart or log splitter, that's different. Build a complete system to do either of those jobs, but keep the implement lift system as it is, even with the new cylinder.
Good morning, Bob. I bought this old GT (a 1971 Wards/Gilson) in November for a Winter project, hoping it would make a good driveway maintenance tool. We have just under 2 acres, all landscaped, to maintain as well. My "project" is nearing completion, so I'm looking for ways to improve what I have. I built a driveway scraper/drag and I've converted the existing dozer blade to a scoop. Both work great and I'm happy with them, but there is still room for improvement.

I'm a tinkerer and always dreaming up new ways of doing things. One area that has room for improvement is power to raise the scoop/bucket. Thus the drive to learn about hydraulics. You've been a great help in that endeaver. Another area of improvement is to use separate power to the two implements by adding an actuator to raise the drag on the rear and using the hydraulics on the front only.

To answer your question, it is a Vickers, driven by driveshaft direct from the engine, rather then by belt. I don't know the model of Vickers. Both the engine and transmission are in VG condition. The hydrauic cylinder and hoses were leaking and I had new 2000 psi hoses made up and the cylinder re-built.

Earlier, I was contemplating changing the cylinder to a 2" bore, which would increase power to the bucket by about 50%. However, finding a cylinder that will fit has proven almost impossible. I could have one built, but I'm retired and funds are scarce. Then it occurred to me that I could accomplish the same thing by increasing pressure. If my Vickers has 500psi, increasing pressure to 1000 psi doubles the power available to the bucket (according to my calculations), but also makes the system faster (not a good thing). To solve that problem, I was wondering about a valve to restrict the flow. The pressure would be the same (I believe). I'm sure the lines can handle the added pressure, the cylinder can handle it, but not sure of the control valve. I can beef up the mechanical portions as necessary.

Anyway, this is all just in the thinking and research stage and if nothing sounds plausible, I'll be happy with it as it is. The bucket makes loading, hauling and dumping so much easier than shoveling by hand. I'll turn 72 next month and anything I can do to make things easier, will keep this old body from aching after a days work on the property.

If you're interested in seeing my old tractor and what I've done to it, there is a running gallery on my website here; http://www.metalsmithpro.com/Gilson.htm. There are a number of threads in this forum showing my progress, too.

Thank you very much for all the advice and knowledge you given me.
 

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G'day, Jack. That's a sharp looking refreshing job on your tractor!

Having never seen a Vickers hydro, my knowledge is limited to generalities. My experience is with the Sundstrand Series 15 hydros. Vickers is an old and well established name in hydraulics, and they make good stuff for the aviation and heavy industry. The GM P/S pump is a Vickers design for aviation from prior to WWII.

Here's a cylinder that I found on eBay. It appears to be a 2" x 4" cylinder, but I'm not positive.

http://www.ebay.com/itm/Wheelhorse-...958?pt=LH_DefaultDomain_0&hash=item5ae490651e

Several of the older GTs may have cylinders that might work for you. A concern that I have is with the cylinder mount on your tractor only being one sided. Over time, increasing the load on that type of mount may cause it to fail, at which point the cylinder rod will get bent. A 50% load increase shouldn't hurt it, but I won't say the same for doubling or tripling the load.

A short lesson on hydraulics. Pumps move oil, work creates pressure. All hydraulic systems have internal leakage due to clearances and lubrication needs. As pressure increases, so does the internal leakage. That's not a big deal, just explaining why the flow does not increase with more pressure. The only way to increase flow from a specific pump is to speed it up.

You're system components appear to be compatible for 1500 psi from what I can see in your pics. The cylinder looks to be consistant with others that I've seen that are rated for 2500 psi. Not too sure about the valve for that much pressure.

Get yourself a 2000 psi glycerine filled pressure guage and a "T" fitting that you can add to the junction of the valve and the pressure line and then add the guage to the "T". Start the tractor and run the cylinder either direction until it bottoms out and read the guage. That's your relief setting. Once you know that, then you can figure out where you have to go with this project. The next step is to calculate the mechanical disdvantage that the cylinder is working with, how much stroke to get how much blade movement.

I hear you on the retirement/lack of funds issue. I've got 2 hobbies and the tractors are the one that is getting short changed. I'm 65 and my company pension hasn't increased in 10 years.
 
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