zz28zz

1. Is it a valve? Is it a pump? Are their different types (in regards to principle of operation)?

2. If it's a valve, how can it be rated in displacement?

3. Will it continue to operate when P/S pump press is lost?

4. Do the right and left hyd hoses have press all the time when eng is running? If so, roughly how much?

5. Is the P/S pump a variable or positive displacement pump?

6. I know there's no permanent center position for the steering wheel but if my steering wheel has a elec trim switch mounted, will the wires eventually get twisted up?

Rookie

iTrader: (4)

Read parts 1, 2, and 3, at the bottom of the page. Enjoy
http://www.pirate4x4.com/tech/billav...ydro_Steering/

Rookie

iTrader: (4)

1. Yes, Yes and Yes (Open center, closed center and open center power beyond) You need open center non-load reaction
2. It's a flow control valve
3.Yes, mine works really well still. (some are real hard to turn)
4. Yes, I believe the power steering pumps can put out between 700-1000psi.
5. I believe positive displacement. Don't quote me.
6. It still maintain a loc to loc position. After a while it might tangle.

No Coast

I'll try and help out. The helm unit used in marine applications is described as an open center unit. When the steering wheel is not rotated the fluid flows through the helm open center and out the return line back to the pump. If the steering wheel is turned to the right, fluid flows out the right port and in the left port, the amount of flow is controlled by an office. The flow is usually described as cc's of flow in one revolution of steering wheel revolution. Twin cylinders need more volume than single's, and more flow reduces the lock to lock revolutions or increases the steering speed.

hallj

Here we go,

It is a directional valve with a geroter style pump to meter oil (cu. In. Per revolution) to the load (cylinder, motor, a balloon, your clothes, engine compartment, the floor under your dash) the size of the geroter set along with the volumetric capacity of the load determines the steering ratio.

The valve section is considered a servo and is a spool in type and is proportional or infinite positioning (not on off like a trim pump solenoid or a starter solenoid)
Is has springs to determine the amount of assist compared to the amount of torque put in the wheel just like the steering in your rack and pinion (the part with tubing connected to it where the steering shaft connects)

If it has a manual steering check valve in it, it will continue to work if you loose your pump belt, it would then be considered manual steering.

There are different valve sections you can choose from. If you have a fixed displacement pump (power steering pump on your boat) you will select an open center type. In it's normal state (no torque into the wheel) it will connect the pressure port directly to the tank port (oil is circulating around and around with little or no pressure, just line losses) If your start putting torque into the wheel, the valve will move proportionally and
Start porting oil from "P" to the "Right" port while equally porting "Tank" to "Left" depending on which way you turn the wheel.
Don't forget that oil is metered through the geroter set which is directly connected to the wheel(it rotates with the wheel). If you move the wheel a little bit back and forth you can feel the spring assembly. The pump will build pressure but only enough to move the load. Power steering pumps are usually capable of 1100 PSI or so, that doesn't mean that there is that much pressure all of the time. There is only enough pressure in the system to move the load required. If you hit an object in the water, you could over pressure the cylinder and hoses because the ports are blocked unless you are putting torque into the wheel.
This is a good application for a relief valve. If pressure gets to high it will allow oil to relieve to the tank. Of course the drive may kick over but it's better than having a broken gimble and a drive hanging from a cylinder or tie bar.


If you have a variable displacement pump as in a pressure compensated pump or a hydrostatic pump (higher end riding lawn mower), one who's displacement is determined by the load requirement. (It sits at a constant pressure no matter if oil is flowing or not) you would choose a closed center valve. You put torque into the wheel and the pump will start increasing in stroke to keep the system at a programmed pressure then stroke back when the demand goes away. The pressure output of the pump is constant and the flow is not.

If you are just driving straight ahead with no torque on the wheel, the cylinder ports are blocked. The amount of pressure on these lines will depend on the load placed at the cylinder.

The steering wheel never centers in the same place so your trim switch will be randomly placed.
They make steering columns with a slip ring for electrical connections like the horn in your car. I'm not sure how many channels are available though. I have only seen one contact for a horn.

I can post some schematics of the valve section tomorrow.

Most marine kits use an Eaton series 6 hydraulic steering unit. There are other brands as well.

There are a few options like "power beyond" and "load reacting".
Power beyond is interesting. I am switching mine over to this option.
This allows oil to be available for other accessories but always giving priority to the steering system. I'm swapping out my Bennet tabs for some heavy duty tabs. I have no reason to run the tabs with the engine off, so I would rather not have to add two more trim pumps. I don't have the space. The steering unit has an extra port for powering auxiliary systems. I will use this with another hydraulic manifold/valve assembly to run the tabs. The manifold will go in place of the existing Bennet pump there by taking up no more space than what is there already. Remember with this setup, you will only be able to run the tabs if the engine is running.

Load reacting will give feedback into the wheel.

I hope that explains the basics.

Jeff

zz28zz

The pirate4x4 site had a lot of good info.
I have some background in hydraulic sys, but never dug into the inner workings of a full hydraulic steering unit.
I can see now that a gerotor is incorporated within the steering unit to pump fluid between the LEFT and RIGHT circuits when no P/S pump press is present (and the check valve has closed preventing fluid from returning to the reservoir). That's pretty slick!

Thx guys!

Just saw hallj's post. That backs up what I was reading while you were typing. Thx for the detailed explanation. It filled in a couple of gaps I had.

I found these pics on pirate4x4's site. They're not labeled very well, but I was able to figure out what was what.

[ATTACH=CONFIG]551269[/ATTACH]

[ATTACH=CONFIG]551270[/ATTACH]

[ATTACH=CONFIG]551268[/ATTACH]

hallj

This is quite helpful as well,
http://www.eaton.com/ecm/groups/publ...t/pll_1585.pdf

If you are buying a new unit, you might as well get the power beyond option. You may want to use it later on.

Jeff