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Old April 28th, 2012, 01:06 PM   #1
liv2mx
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Default school me on hydro steering

so how do you figure what orbital and oil pressure needed.have not really seen many figures on this.everyone just calls a company and they tell them what to get.i had a break
down sheet sent to me on my orbital but have no idea really what it means.
with thousands of different orbitals out there would be nice to have something to work from.
if you want 1 turn lock to lock how do you figure out what you need?
if you have a 2 inch ram how does that play into the figures ?
if you have a double ended ram and want 3 turns lock to lock?

after doing my hydro setup off what someone else told me what will work i would like to be able to figure out the details next time and maybe be able to pick a matched system for what each person wants.

have wheeled with a ton of people with full hydro.have not ever talked to too many people that do not have complaints with each system.
so how smart are you guys on this and how do you make a good system that really works?
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Old April 28th, 2012, 01:25 PM   #2
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You never struck me as much of a "math" guy. I can't help much because I got a complete system from psc. Oh and I have no complaints about mine.
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Old April 28th, 2012, 01:29 PM   #3
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so you never have to fight yours? it always turns good and is fast enough?is it a return to center system? does it have a blow off and keep turning? seems to be a bunch of different variables in each system.
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Old April 28th, 2012, 01:49 PM   #4
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Originally Posted by liv2mx View Post
so you never have to fight yours? it always turns good and is fast enough?is it a return to center system? does it have a blow off and keep turning? seems to be a bunch of different variables in each system.
Fight? No. Fast enough? Plenty for me but I wanted it to be about the same as stock in speed and lock to lock, and it is. Can't say I would really need a return to center set up as mine feels pretty good. That also has to do with the amount of caster you have and the weight of your tires and the air pressure in them. Not sure what you mean by a blow off? If a line blows off then it's going to push your fluid out. In the three years I've had mine I've never had a hose or fitting fail. I believe the hoses are rated way about what a pump like ours is going to put out. Usually a line will only "blow" if it's already damaged or worn thin. I do carry spare line, fittings, and fluid though. Keep in mind that there is no way I would want or need a one turn lock to lock system. I would think if it was one turn lock to lock it would seem plenty fast!
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Old April 28th, 2012, 05:19 PM   #5
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That's all basic hydraulics. The "speed" comes from the oil flow rate compared to the diameter of the cylinder.The pressure is just a matter of how much resistance the cylinder has against it, and will self-regulate according to that up until it hits the setting of the relief valve.
If you were to increase the diameter of the cylinder, and everything else in the system remained the same, then the system would be "slower" because it would take longer to flow enough oil to fill a larger cylinder. If you decreased the diameter of the cylinder, then the system would work faster for the same reason. This is where the main difference between a single ended cylinder and a double ended cylinder comes in. The single has only 1 rod taking up space, so the volume of that side is effectively smaller then the volume of the area on the other side of the cylinder head, or gland. This makes it slower in one direction (pushing the rod out) because it has a greater volume to fill with the same flow rate. A double ended cylinder is basically balanced according to flow rate. The area on each side that needs to be filled is equal, since both side have a rod of the same diameter filling up some pf the area.
Pressure is nothing more then the resistance to flow. In this system, if you raised the tires and turned the wheel while monitoring the pressure, there would be very little pressure. If you put the tires on the ground with a large rock against one, and tried turning against that rock, there would be considerably more pressure. If you turned the wheel to the lock position, and then tried turning more, even though the system is mechanically stopped, then you would see the set pressure of the relief valve. If the pressure needed for the tires to move the rock out of their way is lower then the set pressure of the relief valve, then the rock would move. If it take more pressure then what the relief valve is set at, then the system would sit still and the oil would flow over the relief valve and back to the reservoir.
The flow rate of the steering valve (orbital or orbit-roll) is basically a max flow rate that it can handle. Obviously it cannot push out more oil then it gets from the pump. The flow rate of the system is completely determined by the pump, and the pressure relief valve is built into a automotive type power steering pump. The relief valve can be modified to adjust the setting, but the flow rate cannot be modified in that type of pump.
The problem most people have when piecing a system together is using a steering valve that is rated too low, often taken from a fork lift. The steering cylinder on those are usually very small diameter, so flow rate for the original system is very low comparatively. They then try to modify the pump to make the system work "better". What those two problems combined create is a lot of heat as the low flow rate at a higher pressure just forces the system to run over relief sooner and more often. Flow without work = heat.
Look at it this way. If the pump flows 5 gallons a minute (just picking numbers out of the air, not necessarily what any pump actually does), but the steering valve came off a forklift that only needed an output of 2 gallons a minute, then where does the excess oil go? It flows over the relief valve in the pump, keeping the system at max pressure any time the wheel is turned.
The other problem is the actual mounting position of all of the steering components, and the resistance against the tires turning. If the system is not working as expected, and the flow rate of the steering valve is not the issue, then I would suggest looking at this before even considering any modifications to the pump.
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Old April 28th, 2012, 07:57 PM   #6
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so how do you decide how much volume the orbital should have? i am running a stock gm pump.i will change it if i feel it does not work correct.i have drove a couple that you had to turn the wheel 4 times to stop.that sucked.my ram is a 2x7 1/2 stroke single end. he says they make them to flow almost the same pushing or pulling.that is why i got that ram.
i know you can also change the ram to be quicker or slower depending on were it is mounted on your knuckles.
i just dont understand how to pick a orbital. i called scott at sunfire and he said there is a formula that is used to decide how big a orbital and how many lock to lock turns you get.he did not tell me it though.
i know the lines are also a big factor on how your system works.if they are not big enough they will not give enough oil.

some good info you gave yota bill.just trying to understand the system.there are a bunch of different ideas on how to make a system work out there.
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Old April 28th, 2012, 08:59 PM   #7
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The oil flow of the stock pump is probably sufficient. If you want to know what it flows, then first calculate how many RPMs it turns at a given engine RPM, I would suggest calculating it at idle. That's pretty easily done by comparing the size of the pulleys. Then, disconnect the output line and put it in a measuring container, rotate the pump by hand 1 full turn, or 10 full turns (easier) and multiply the amount that it has pumped at that point by the RPM already calculated by the pulley size. Don't forget to move the decimal point if you go with 10 full turns. That will tell you how much oil is going in to the orbital at idle. You can do the math to calculate it at different engine RPMs from there as well.

Steering valves have two separate ratings for oil flow. One is the flow rate, or what it will accept, usually noted in gallons per minute (GPM). That number you would need to look up according to the numbers on the unit, and is what needs to match the flow rate of the pump. The 2nd rating is the output flow rate, and that's the one that you seem to be more concerned with. It is also the one you can easily measure. It is normally noted in cubic centimeters per revolution (cm3/r) or cubic inches per revolution (in3/r). To measure it, simply supply it with oil from a suspended container (gravity feed), rotate the shaft 1 full turn, and measure the amount of oil that comes out. Compare that to the area of the cylinder that it needs to fill, and you can figure out the number of turns to full stroke. If the steering valve displaces 1/3 of the total amount of oil the cylinder needs to move from closed to extended, then it will take 3 full turns. If the steering valve displaces the same amount as what the cylinder needs to fully extend or retract, then it will go lock to lock in 1 turn of the steering wheel, and be very fast and difficult to have any fine control.

On a side note, if you want to get the same number of turns lock to lock in both directions (like a double ended cylinder will do), and at the same time increase the effective force applied to the steering system without raising the pressure, you can install 2 single ended cylinders of the same size and plumb them together, but point them in opposite directions. This would make one cylinder retract as the other extends, and vice versa. It would also increase (almost double) the surface area of the gland that the oil is pushing against to move the cylinder, which would also almost double the effective force of the system as a whole, while using the same pressure. You would still need a tie rod connecting the two tires together, or they would end up moving separately of each other. Of course, this would also double the amount of oil needed to move both cylinders fully, or double the number the number of turns of the steering wheel.

For example, you are already using a 2" diameter cylinder with a 7.5" stroke. If you replaced that cylinder with 2 cylinders that both had a 1" diameter and a 7.5" stroke, but pointed them in opposite directions, you would use the same amount of oil to go from lock to lock, have the same effective force, but the steering wheel would turn the exact same amount in both directions. If you kept the cylinder you have, and added another one the same size, you would double the effective force without changing the pressure, but the systems speed would be cut in half, and the steering wheel would again turn the exact same amount in both directions.

4 Wheel steer with 3 separate modes (crab, 4 wheel opposed, and 2 wheel) can also be done in a similar fashion, with the addition of a simple directional valve like the ones used on log splitters.

Last edited by Yota Bill; April 28th, 2012 at 09:06 PM.
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Old April 28th, 2012, 09:09 PM   #8
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Just wondering, who is "he"?
You cannot get a single ended, double acting cylinder to flow the same amount in both directions, because the rod is in one side taking up some space. The larger the diameter of the rod, the more space it takes up, and the more differential there is in the cylinder. For the two sides to be even close would mean a rod that is very small, which would make it more susceptible to being bent under the force of the system.
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Old April 28th, 2012, 10:00 PM   #9
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I just read the answers regarding the hydraulic steering question. Good explanations.

I have a question regarding a portion of the answer. I figure that 2, 1"x7.5" cylinders would use about 1/2 of the fluid of a single 2"x7.5" cylinder, not be equal. The surface area of each 1" ram would be .7854 square inches or 1.56 square inches for the pair. The surface area of the 2" ram would be about 3.2 square inches.

Since the length of the cylinders remains the same wouldn't the volume then be the same proportions as the surface area of the rams?

Hope I am not confusing a the explanations given so far and surely hope I am not messing up the thread with bad math.
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Old April 28th, 2012, 10:04 PM   #10
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I didn't do any math, just guestimated.

*edit*


just did the math and got the same numbers as you, so you are correct. Pi makes guestimating wrong.

Last edited by Yota Bill; April 28th, 2012 at 10:07 PM.
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Old April 28th, 2012, 10:07 PM   #11
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Even though I am not the OP, thanks again for the explanations.
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Old April 29th, 2012, 05:45 AM   #12
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Erin,
You can't do the math on oil volumes till you also know the diameter of the rod. There are 2 different ways to calculate volume. I use one that doesn't worry about pi (3.14159...) First you determine the area (diameter based) and then multiply it by the stroke. Here's the formula I use.
Diameter squared (diameter x diameter) x .7854 x stroke. (.7854 is a constant) So,

2^2 x .7854 = 3.1416 (this is the area of your 2" cylinder)

3.1416 x 7.5 stroke = 23.562 cubic inches. This is the amount of oil it will take to stroke your cylinder from fully compressed to fully extended.

Now, to calculate the volume required to retract your cylinder, you will need to subtract the area that the rod takes up from the area of the cylinder. For easy math, let's say you have a 1" diameter rod. Using the formula above, the area of your 1" rod is .7854 square inches. (see that constant number .7854?) Now, .7854 square inches x 7.5" stroke = 5.8905 cubic inches.

So, it takes 5.8905 square inches LESS to retract your cylinder than extend it, or 17.6715 square inches.

Extend = 23.562
Retract = 17.6715
Difference = 1.333%

So, Yota Bill is right, there is no way you can get a single ended ram to work both ways lock to lock. However, you may not notice the difference. Assume 3 turns lock to lock to extend. To retract, divide 3 by 1.333 = 2.25 turns lock to lock to retract.
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Old April 29th, 2012, 08:42 AM   #13
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See Erin, you're in the "math" zone now! It's good to see you wanna know the how's and why's of a system though.
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Old April 29th, 2012, 09:46 AM   #14
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http://www.pirate4x4.com/tech/billav...ing/index.html

Calc
http://www.pirate4x4.com/tech/billav.../Steering.html
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Old April 29th, 2012, 06:44 PM   #15
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here is a good arcticle on making a stock chevy pump better.

i plan to give this to joe...

http://westtexasoffroad.homestead.co...rsteering.html

Last edited by liv2mx; April 29th, 2012 at 06:52 PM.
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Old April 29th, 2012, 06:50 PM   #16
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eagle machine gauranteed me i will be able to pull my steering wheel off and turn with my fingures. if you watch any of these guys rigs work they are fast and turn the same both ways.i have done excactly what brian cole told me so we shall see how it works.

i just want the info so i can understand how to mach a system. thanks for the good info guys. i will let you know if my system works or not.
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Old April 29th, 2012, 08:04 PM   #17
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Quote:
Originally Posted by Yota Bill View Post
The oil flow of the stock pump is probably sufficient. If you want to know what it flows, then first calculate how many RPMs it turns at a given engine RPM, I would suggest calculating it at idle. That's pretty easily done by comparing the size of the pulleys. Then, disconnect the output line and put it in a measuring container, rotate the pump by hand 1 full turn, or 10 full turns (easier) and multiply the amount that it has pumped at that point by the RPM already calculated by the pulley size. Don't forget to move the decimal point if you go with 10 full turns. That will tell you how much oil is going in to the orbital at idle. You can do the math to calculate it at different engine RPMs from there as well.

Steering valves have two separate ratings for oil flow. One is the flow rate, or what it will accept, usually noted in gallons per minute (GPM). That number you would need to look up according to the numbers on the unit, and is what needs to match the flow rate of the pump. The 2nd rating is the output flow rate, and that's the one that you seem to be more concerned with. It is also the one you can easily measure. It is normally noted in cubic centimeters per revolution (cm3/r) or cubic inches per revolution (in3/r). To measure it, simply supply it with oil from a suspended container (gravity feed), rotate the shaft 1 full turn, and measure the amount of oil that comes out. Compare that to the area of the cylinder that it needs to fill, and you can figure out the number of turns to full stroke. If the steering valve displaces 1/3 of the total amount of oil the cylinder needs to move from closed to extended, then it will take 3 full turns. If the steering valve displaces the same amount as what the cylinder needs to fully extend or retract, then it will go lock to lock in 1 turn of the steering wheel, and be very fast and difficult to have any fine control.

On a side note, if you want to get the same number of turns lock to lock in both directions (like a double ended cylinder will do), and at the same time increase the effective force applied to the steering system without raising the pressure, you can install 2 single ended cylinders of the same size and plumb them together, but point them in opposite directions. This would make one cylinder retract as the other extends, and vice versa. It would also increase (almost double) the surface area of the gland that the oil is pushing against to move the cylinder, which would also almost double the effective force of the system as a whole, while using the same pressure. You would still need a tie rod connecting the two tires together, or they would end up moving separately of each other. Of course, this would also double the amount of oil needed to move both cylinders fully, or double the number the number of turns of the steering wheel.

For example, you are already using a 2" diameter cylinder with a 7.5" stroke. If you replaced that cylinder with 2 cylinders that both had a 1" diameter and a 7.5" stroke, but pointed them in opposite directions, you would use the same amount of oil to go from lock to lock, have the same effective force, but the steering wheel would turn the exact same amount in both directions. If you kept the cylinder you have, and added another one the same size, you would double the effective force without changing the pressure, but the systems speed would be cut in half, and the steering wheel would again turn the exact same amount in both directions.

4 Wheel steer with 3 separate modes (crab, 4 wheel opposed, and 2 wheel) can also be done in a similar fashion, with the addition of a simple directional valve like the ones used on log splitters.
that is some very easy to understend terms. nice job.
the guys running rear steer down south are running 2 pumps,2 inch se ram's. they are stupid fast.
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