How does automotive type power steering work?

[etpm]

I know, a really generic question so I will narrow it down. I am using a power steering cylinder and valve combo made as an add on for a YM2310 Yanmar tractor to add power steering to my YM2310 tractor. I will most likely be using a power steering pump instead of the tractor hydraulics because I want to keep them separate.
I think the power steering valve on the cylinder must be the open center type, otherwise a pressure limiting valve would always be forced open when the power steering cylinder is stationary but not at the travel limits.
From what I have read the power steering cylinder I bought new from a reputable dealer has a pressure limit of 1800 PSI. The dealer provided no documentation and has not responded to my emails so I don't know for sure. If 1800 PSI is the limit and the pump I buy is able to provide more I guess I will need to buy some sort of valve that bypasses higher pressure oil to the low side plumbing that goes to the oil reservoir. I guess I better get a gauge too.
So I am asking if my descriptions above are correct and suggestions regarding which bypass valve I should buy and where to buy.
Thanks,
Eric

 

[oldnslo]

Are you using a steering pump with built in reservoir? If yes I believe the system relief is built in but you would have find a model code to confirm this.

yes you would require an open center steering unit so that in neutral position oil just circulates back to tank.

 

[PILOON]

W ell I know most are hydraulic but there are some that are electric as well.

 

[zzvyb6]

Cars and trucks use open center hydraulic systems. In a rack and pinion type "steering gear" A pump (specified in gallons per minute) supplies flow all the time. Flow rates are generally in the 2 to 4 gallons per minute. The steering gear "Top Hat" contains a special pinion with a valve assembly attached to it. The "T-bar" produces a mechanical connection to the pinion gear which engages the rack. A valve body is also in the top hat and surrounds the T-bar. When force is applied to the steering wheel/steering column, the T-bar twists a bit providing mechanical force to the rack AND the valve also opens a bit as a result of the twist. As the valve opens, hydraulic flow is diverted to lines into the rack body to push the rack in the desired direction. This action also untwists the T-bar in a closed loop type control. So, you get to "feel" the rim force induced by the front wheels but not all of it. The thicker the t-bar, the more mechanical force you feel because there is less valve opening and thus less hydraulic assist. Likewise, a force induced by the steered wheels also engages the pinion which twists the T-bar, which adds hydraulic flow to reduce the incoming rim force. A recirculating ball gear essentially works the same way. A rim force or a Pitman arm force is reacted by a valve assembly which has a T-bat and hydraulic ports to close the T-bar twist. Note that most tractors have closed center steering and a velve with no T-bar. That's why your steering wheel can assume any rotary position when flow is cut off. This is not acceptable to vehicle drivers.

 

[etpm]

That was a good post. Since I will be using a cylinder and valve meant for adding to a tractor I had better determine which type of valve I have. I guess when the valve, which is a push/pull type type, is in the neutral position I should be able to blow into the intake and the air should flow just as freely out of the exhaust if the valve is the open center type. If I cannot blow air through then the valve must be of the closed center type. If closed center then I cannot use a car power steering pump. Tomorrow I will determine the valve type on my power steering cylinder. Thanks again for your very informative post.
Eric

 

[airbiscuit]

A lot of folks are using automotive electric poser steering.

 

[airbiscuit]

 

[airbiscuit]

 

[etpm]

A lot of folks are using automotive electric poser steering.

Yes, I know. I however will not. If interested why just search for "crazy idea?" thread.
Thanks,
Eric

 

[airbiscuit]

Others may want to try this approach. It's pretty slick actually.