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Discussion Starter #1 (Edited)
I know - it's not possible to fail-proof anything. But I'm building an offroad-oriented motorhome that I want to convert over to a full hydraulic steering setup, and I want to make it as safe as possible. This is a BIG truck (16,000lbs empty) and I'm going to be driving it on public roads. Plus, I'm going to be living in it full-time and, well, I don't want to crash my house.



The M35A2's all came with manual steering, and it's actually not as bad as I was expecting; at least when the truck is moving and the road is smooth/paved. But maneuvering in parking lots and steering through rough terrain is absolutely brutal. The M35A3's were outfitted with air-assisted power steering systems, and those air-assisted power steering systems were also retrofitted to some of the M35A2's. But I'm not at all interested in going that route. There is limited room to retrofit another (power) steering box, and no real way to run any type of crossover steering linkage. So here I am. I'm NOT asking whether or not I should run full-hydro steering on the street, so please don't turn this into another debate about whether or not full-hydro steering is legal/safe/etc. I'm comfortable with the idea of running full-hydro steering on the street - I'm only trying to figure out how to design and build the best/safest system for this application.

I've read through all the relevant threads that I could find, and I've read Billavista's tech articles. I know that all the components need to be carefully selected in order to create a balanced system, and let's just assume that the whole system will be regularly inspected and properly maintained. In some of the past discussions about running full-hydro steering on the street, we've talked about the back-up systems that they use in things like airplanes. I'd like to figure out whether it's possible/practical to design/build some kind of similar redundancy into this kind of steering system.

I'm most concerned about blowing pressure lines/hoses, as that's probably the type of failure that's most likely to result in a total loss of steering, right? I'm not too concerned about losing power/pressure, as that wouldn't be any worse than what I've got now (manual steering). But I guess the steering unit could fail somehow, or the ram/s could blow apart. Am I overlooking any other (realistic) types of potentially catastrophic failures that should be considered/addressed?

Having two completely separate/redundant hydraulic steering systems seems like one obvious solution, and that wouldn't be too difficult. But I'm wondering if I really need to double-up on EVERYTHING.

Is there any way to design/build a system that has two separate hydraulic circuits without using two pumps? I just don't have enough room to install a 2nd pump (at least not one that's engine-driven). I'm planning on using the stock 5-ton/LDS multifuel engine's power-steering pump. The specs on these pumps vary a little bit, but they're all positive-displacement type pumps, and they put out between 5-6gpm at 1000-1500psi (more info here). Could that be done with check-valves or something? Doesn't seem like that would be a problem.

What about the reservoir/s? Would it be a bad idea to use a common reservoir? I know that eventually a blown line would drain the system, but I'm going to have an extra-large reservoir (10-20 gallons) because I've also got a transfercase-mounted hydraulic PTO unit on this vehicle. I've got to use multiple reservoirs anyway due to space constraints, but I would like to be able to run all of the hydraulic fluid through the same filtration system if at all possible.

And what about the steering unit? I'm totally stumped here. No idea how to control two separate hydraulic systems with one steering unit. Is it just a matter of creative plumbing, or would I need a different type of steering unit? I definitely want to use something that's load-reactive, and I would like it to have a power-beyond port, but that's not essential.

After considering all the options (at least that I'm aware of), I think I'd like to use two cross-linked rams, mounted sort of like this:



But can I use unbalanced rams that aren't cross-linked?

I would consider using a single/balanced/centered ram, but I'm not thrilled about the side-loads. Especially on such a big heavy vehicle that's going to see a lot of street miles. Plus I like the fact that with two rams, I'd still have a backup if I lost one. More common and less expensive too (service/replacement).

Not sure how I'd use one (or more) of these, but I thought it was pretty cool:

 

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The number one thing I can think of as far as safety in a hydraulic system that has the potential to shut down or lose its source of pressure is an accumulator. We use them in our windturbines for emergency situations where the turbine has to shut down. When this happens it kills power to the hydraulic pump. The accumulators are a pressurized storage tank and carry enough capacity to pitch the blades back stop and apply brakes. If I ever built a fully hydro system for the street or where I would want some sort of back up in case of motor failure this is how I would do it. It will also help if you want to use one pump with two systems or possibly your back up. Either that or I would rig some sort of electrical back up pump.

For your steering of two rams like that I think your are on track with the creative plumbing. Take the time to draw out a line diagram and plan your system like you want it. You could valve it like you were saying to where if one ram failed you would have the other, but I think your steering would be a bit fast all of a sudden. If im thinking right if your using two rams plumbed like you have drawn you would need a orbital valve that would pump twice as much per turn as normal because it is feeding two rams instead of one.

I think a common reservoir would be best to prevent unless you can make sure your pick up will always be fed from the resivor/s without sucking air.

For filtration just put it inline before your pump and after your reservoir. That way only clean fluid enters the pump and there for the rest of your system. This will also eliminate the need for a high pressure filter which tend to be bulky.

As far as lines I would recommend getting the best/highest rated lines you can by the best manufacturer you can. This along with careful routing should minimize a chance of a blown line. If you want to further lower the chance run hard line wherever possible and keep your hoses to a minimum.

Like you say proper maintenance is key. We check out stuff every 6 months to keep a turbine from having the possibility of running away.
 

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have you looked at the inline control valves that howe uses for rack-n-pinion setups allowing for hydro assist? theyre small and compact

just a thought, no information for your full hydro
 

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Quality parts and hoses, standard setup, I'd run it. All that other shit, more shit to go wrong. I'd say keep it simple.
 

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Discussion Starter #5
have you looked at the inline control valves that howe uses for rack-n-pinion setups allowing for hydro assist? theyre small and compact

just a thought, no information for your full hydro
No! But that sounds like JUST what I need for my Tacoma. Stock rack and pinion fawking sucks...
 

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Discussion Starter #6
The number one thing I can think of as far as safety in a hydraulic system that has the potential to shut down or lose its source of pressure is an accumulator. We use them in our windturbines for emergency situations where the turbine has to shut down. When this happens it kills power to the hydraulic pump. The accumulators are a pressurized storage tank and carry enough capacity to pitch the blades back stop and apply brakes. If I ever built a fully hydro system for the street or where I would want some sort of back up in case of motor failure this is how I would do it. It will also help if you want to use one pump with two systems or possibly your back up. Either that or I would rig some sort of electrical back up pump.

For your steering of two rams like that I think your are on track with the creative plumbing. Take the time to draw out a line diagram and plan your system like you want it. You could valve it like you were saying to where if one ram failed you would have the other, but I think your steering would be a bit fast all of a sudden. If im thinking right if your using two rams plumbed like you have drawn you would need a orbital valve that would pump twice as much per turn as normal because it is feeding two rams instead of one.

I think a common reservoir would be best to prevent unless you can make sure your pick up will always be fed from the resivor/s without sucking air.

For filtration just put it inline before your pump and after your reservoir. That way only clean fluid enters the pump and there for the rest of your system. This will also eliminate the need for a high pressure filter which tend to be bulky.

As far as lines I would recommend getting the best/highest rated lines you can by the best manufacturer you can. This along with careful routing should minimize a chance of a blown line. If you want to further lower the chance run hard line wherever possible and keep your hoses to a minimum.

Like you say proper maintenance is key. We check out stuff every 6 months to keep a turbine from having the possibility of running away.
Thanks for the input. I read your posts about the accumulators in an old thread about this. But if I lose pressure due to a pump failure or the engine dying or something, I'll still be able to steer. I'm much more concerned about blowing a line, in which case, and accumulator is just going to spill more hydraulic fluid. And if I use two rams, I would size them so that they each provided 50% of the total power I need. So if I lost one of the rams, I would lose half the power. The steering wouldn't get faster.
 

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Discussion Starter #7
Quality parts and hoses, standard setup, I'd run it. All that other shit, more shit to go wrong. I'd say keep it simple.
I agree, and if it comes down to it, I will. But I'd like to see if I can design/build any additional safety into this system.
 

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I drove a 1976 Peterbuilt for a couple years that was equipped with air assist steering, it wasn't that bad.

Another option would be a used power steering set up from a 1980-2000 Pete or KW?
 

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why go to all this trouble and use a single reservoir? The failure scenario you are planning for is blowing a line and if that happens you could run out of fluid without noticing and then you are back to square one. cool rig though.
 

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Discussion Starter #10
I drove a 1976 Peterbuilt for a couple years that was equipped with air assist steering, it wasn't that bad.

Another option would be a used power steering set up from a 1980-2000 Pete or KW?
I don't want to deal with the stock draglink, and there's not room for crossover steering linkage. It's more about packaging and geometry than power.
why go to all this trouble and use a single reservoir? The failure scenario you are planning for is blowing a line and if that happens you could run out of fluid without noticing and then you are back to square one. cool rig though.
Didn't see that as much of a problem. Would be stupid-simple to incorporate some type of low-level sensor into the reservoir. You've got a good point though.
 

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Why not go for hydroassist on the truck. Put a Sweet Valve on the steering shaft and a big hydraulic cylinder on the axle.
 

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Discussion Starter #12
Why not go for hydroassist on the truck. Put a Sweet Valve on the steering shaft and a big hydraulic cylinder on the axle.
I don't want to deal with the stock draglink, and there's not room for crossover steering linkage. It's more about packaging and geometry than power.
Did you see this post?
 

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And if I use two rams, I would size them so that they each provided 50% of the total power I need. So if I lost one of the rams, I would lose half the power. The steering wouldn't get faster.
It would if you were to cap off the bad cylinder.

why go to all this trouble and use a single reservoir? The failure scenario you are planning for is blowing a line and if that happens you could run out of fluid without noticing and then you are back to square one. cool rig though.
So carry extra oil??


When you mention "Blowing a line", do you mean just a sudden rupture, or something ripping a line off the cylinder? I ask because I don't see a sudden failure likely. A quick look around (http://www.pirate4x4.com/tech/billavista/PR-Hydro_Steering/index2.html) tells me that automotive pumps put out less than 1500 psi, and there is hose available to 6000 psi. (http://www.gates.com/brochure.cfm?brochure=3044&location_id=3824) That gives you a FS of 4.
 

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Over Centre Valve , on or right next to the steering cylinder ...

Blow a hose ..
Oil dumps..
steering cylinder stays still , so you can hit brakes

????

Matt.
 

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I know you said you didn't want to do hydro assist...but I doubt it could be any harder than designing a "fail proof" full hydro setup.

Throw up some shots of the stock steering and see if that helps get you some ideas.
 

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Discussion Starter #17
If you use a DE ram as part of tie rod then you don't have to mess with the stock draglink or do cross over steering.
Not sure I'm following you. I understand how you could used a DE ram with hydro-assist, but I want to get rid of the stock steering box and drag-link and there's no room for cross-over steering linkage.

It would if you were to cap off the bad cylinder.
Yeah, I would carry spare parts to cap off a blown cylinder, replace a line, etc.

When you mention "Blowing a line", do you mean just a sudden rupture, or something ripping a line off the cylinder? I ask because I don't see a sudden failure likely. A quick look around (http://www.pirate4x4.com/tech/billavista/PR-Hydro_Steering/index2.html) tells me that automotive pumps put out less than 1500 psi, and there is hose available to 6000 psi. (http://www.gates.com/brochure.cfm?brochure=3044&location_id=3824) That gives you a FS of 4.
Either I guess, but I think something getting hit/pulled/damaged would be the most likely failure scenario.

Over Centre Valve , on or right next to the steering cylinder ...

Blow a hose ..
Oil dumps..
steering cylinder stays still , so you can hit brakes

????

Matt.
Thanks, someone else just told me about those last night. Would be cool if the steering returned to center in the event of a total failure. Should help with braking/slowing down/stopping.

I know you said you didn't want to do hydro assist...but I doubt it could be any harder than designing a "fail proof" full hydro setup.

Throw up some shots of the stock steering and see if that helps get you some ideas.
Harder? That doesn't really have anything to do with it. And trust me, there's no room from cross-over steering linkage. Sure, I could get creative, but at the point where I'm using bell-cranks and all that bullshit... I'd rather just go full-hydro.
 

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Harder? That doesn't really have anything to do with it. And trust me, there's no room from cross-over steering linkage. Sure, I could get creative, but at the point where I'm using bell-cranks and all that bullshit... I'd rather just go full-hydro.
I'm pretty sure if I wanted a full proof system I'd find a way to make hydro assist work, especially if you're worried about rupturing a 3000+ psi hydraulic line doing 55 down the freeway.
 

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My Dodge ripped the ball stud out of the socket on the passenger side TRE. This happened making a u-turn in a parking lot, after just having dropped a 10k load I had towed a few hundred miles down the highway. It hadn't seemed loose or anything; I was just turning back to opposite lock and suddenly it got a whole lot easier to move the wheel.

'Fail proof' is a nice idea, but a mechanical linkage isn't the answer either.
 

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Discussion Starter #20
Where did that number come from (3000psi)?

I'm much more concerned about the single-circuit brakes on this big old truck. I've completely rebuilt the entire braking system, but it's still not what I'd call fail-proof. Not even close. If there's a pressure-loss anywhere in the system, bye-bye brakes...
 
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