Changing Power Assisted Steering

What you propose is possible with the right considerations. First off, I'll tell you that without knowing the specifics of the equipment already installed, and the specifics of the equipment you plan to install a reliable answer cannot be given. The design of this type of system should be looked over by a qualified Hydraulics specialist. Good people are killed mis-using hydraulic systems every day.

First, you need to ensure you can supply the proper flow/pressure to run ALL functions simultaneously at full volume with the single pump. Check this first.

Second, Any time you can add a relief valve to your system, the better off you will be in the event of a failure. You should add this relief valve (probably came installed from factory) just after the pump, and set this to divert flow back to tank in the case of a problem down the line in the system causing over-pressurization.

Third, You should never consider the counterbalance or check valves which are inline with your cylinders to provide any function other than a last resort "in case of failure" safety function, and they will only provide a safety function if you don't rupture a hose or fitting on the cylinder side of the valve. Do not rely on these to hold your load in an operational setting.

You WILL have pressure drops across each component in your system, it is mandatory to include these into your calculations when choosing components.

It is not advisable to connect your control valves in series, you should plumb these in parallel to the pump, with a pump fully capable of running both (or all) functions at full pressure/flow at the same time.

Your steering valve is a proportional valve correct? If not, you cannot achieve proper steering capabilities as the valve will either be full on or full off. Proportional valves provide increased flow proportional to the input value for smooth operation of things such as drive wheels, steering rams etc.

If you plumb your steering valve ahead of your lift valve you will see erratic behavior in one function while operating the other. This can be a dangerous situation when holding a load, the forklift will become a dangerous piece of machinery. Do not do this.

ALL the oil WILL always go back to tank (unless it's leaking onto the ground), where else would it go?

What you propose can be done, but the time, engineering, and labor to achieve the proposed project may go above and beyond your project budget. Another thing to consider, is that after spending all this time and money on this project, it might not work as planned if you did not have a competent Engineer in the hydraulics field check your calculations.

Think you MUST know BEFORE starting your project:

1. What is your fluid? Viscosity? ambient operating temperatures?

2. What is the required flow for ALL components in the system? IE how much oil will your steering cylinder require to fully extend? How fast do you want this to happen? Lift cylinders? drive wheels? etc etc etc. (assume they will all be running at once)

3. What is the required pressure for each component, including pressure drops?

Questions you should ask yourself:

Are you able to calculate all these things properly?

Do you know someone who specializes in hydraulics from which you can get some help?

Is there any chance someone could possibly get hurt or killed due to a faulty controls system on this forklift? (I'll answer that one for you) Answer: YES, there absolutely is.

If this is not done correctly, and someone gets hurt/killed, the responsibility of that persons injuries will fall on the individual who modified the forklift from it's stock condition. That person will be you.

If you understand all these things, and can acquire some professional help, then you have yourself a project. If you cannot get some competent help on this project, I must advise you to stop all forward momentum on this project until said help can be arranged.

Yes you can do it by fitting a Priority valve between the pump and the directional valve and the steering unit. It is not a job for the uninitiated, go to Danfoss or Eaton distributor and ask them to advise you. Selection of a priority valve and orbitrol steering unit is an expert job.

Regards

Oliver Dunthorne

Hydraulic Engineer