Ascinder's 1-Ton VX... Cont'd

[PK]

A few words of caution with sizing up your power steering, from a Fluid Power Engineer with 45 years experience in circuit design, including power steering circuits.

1. Will you be driving this vehicle on the roads?? In Australia, and most of the rest of the civilised world, Orbitrol units are not legal for on road use. Stupid but true. The Orbitrol units do not have the safety features supposedly found in the sector and ball-nut type power steering boxes.

2. Try and find a larger flow dedicated power steering pump if your first choice is not large enough. 5 and 7 GPM power steering pumps are readily available, and still have all the inbuilt features that a commercial gear pump won't have.

3. If you have to go to a commercial pump, try and find a high speed vane pump, rather than a gear pump. Do not under any circumstances use a gear pump with an aluminium housing. They cannot support the sustained heat and high pressure, nor the high revs.

4. You are correct that a commercial pump is not normally built to take side loads like a belt drive. Your idea of an aluminium plate with a bearing in it, is very limited. Most pump shafts are too short to protrude through the aluminium plate and still engage the belt pulley. To use your idea you will also need a stub shaft made to extend the pump shaft - female to mate with the pump, male to mate with the pulley. Some commercial pumps can be ordered with an "overhung load adapter" built into the pump housing. This does allow them to take the belt drive side force.

5. A dedicated power steering pump has 2 vital valves built into the pump. A pressure relief valve, and a pressure compensated flow control valve. If you use a commercial type pump you will have to purchase, mount, and plumb up these 2 extra valves.

6. Don't forget that the larger the commercial pump flow, the larger the reservoir required. Rule of thumb is 3 x GPM for the reservoir size. This can be reduced down to 1 x GPM if you install an additional cooler. Dedicated power steering pumps use some internal trickery to get away with smaller reservoir sizes. They also use longer routing of the return lines to allow heat to dissipate prior to returning to filter and reservoir.

7. Whatever you do, work out your actual flow calculations very carefully. Engine RPM range, dia of crankshaft pulley and dia of pump pulley and the displacement of the pump in cubic inches/rev (or cc/rev) should give you the right answers. You need enough flow at idle to slowly turn your steering, and not tooo much at high engine revs.


That is probably enough for now.
If you need any help sorting through the options of the Orbitrol units give me a yell. Unless you have been especially trained in military driving techniques, avoid any orbitrol unit that will give you live feedback. Otherwise you will break your thumbs as the road wheel hits a rock and the steering wheel spins uncontrollably out of your hands.


I have been retired for a few years now, but still do some consulting work when I am dragged back for particular problems.



PK

[Ascinder]

A few words of caution with sizing up your power steering, from a Fluid Power Engineer with 45 years experience in circuit design, including power steering circuits.

1. Will you be driving this vehicle on the roads?? In Australia, and most of the rest of the civilised world, Orbitrol units are not legal for on road use. Stupid but true. The Orbitrol units do not have the safety features supposedly found in the sector and ball-nut type power steering boxes.

This has been gone over earlier in the thread and on other forums ad nauseum. The DOT does not specifically prohibit hydraulic steering, but does stipulate that steering must be connected through a mechanical linkage. We have garbage trucks in the states that steer purely through hydraulic steering so it is being done somehow. Most police here don't know and don't care about any obscure legalities regarding this.

2. Try and find a larger flow dedicated power steering pump if your first choice is not large enough. 5 and 7 GPM power steering pumps are readily available, and still have all the inbuilt features that a commercial gear pump won't have.

Most higher flow pumps that I have come across are just hot rodded (bored out) conventional power steering pumps. They burn out under full hydro use very often and are expensive to replace. What inbuilt features are you referring to? Several of the gear pumps I have looked at have built in flow and pressure regulators. What would a conventional pump have/need besides those?

3. If you have to go to a commercial pump, try and find a high speed vane pump, rather than a gear pump. Do not under any circumstances use a gear pump with an aluminium housing. They cannot support the sustained heat and high pressure, nor the high revs.

The things I have read point in a completely opposite direction. The aluminum dissipates heat better than steel. My "high performance" KRC pump is aluminum with the steel pump being half the price. The manufacturer told me they went to aluminum because the steel wouldn't hold up at high rpm/heat. The gear pumps I have looked at are all rated well over 3000 psi and 4000 rpm constant speed. Manufacturers have stated in letters that they are able to sustain higher rpms for short periods with no problems. Several people have been running these pumps in this fashion for years with no ill effects. The gear pumps(and a fair amount of vane pumps can be had for ~$100. Versus replacing a ~$3-400 suped up power steering pump at about the same rate, I'll take my chances with the gear driven models(although the vane pumps are fine too I understand they don't do as well at high pressure or life expectancy)

4. You are correct that a commercial pump is not normally built to take side loads like a belt drive. Your idea of an aluminium plate with a bearing in it, is very limited. Most pump shafts are too short to protrude through the aluminium plate and still engage the belt pulley. To use your idea you will also need a stub shaft made to extend the pump shaft - female to mate with the pump, male to mate with the pulley. Some commercial pumps can be ordered with an "overhung load adapter" built into the pump housing. This does allow them to take the belt drive side force.

I have looked into this as well. A half inch thick aluminum plate simultaneously mounts the pump and provides a pocket for the bearing. The bearing is a ~$30 NTN deep groove single roller bearing rated at thousands of pounds of load and tens of thousands of rpms. It is under 3/8" thick. The pump shafts I am looking at would protrude through the plate and bearing with 3/4 of an inch to spare. Even more if you consider that the bearing only needs to be retained with a small lip around the rim so the pulley would be able to mount right up to it "into" the aluminum plate. This eliminates the need for a stub shaft and all its additional complications. The pumps I have seen with overhung load adapters have all been clutched units which cost 7-8 times as much as the unit I am considering.

5. A dedicated power steering pump has 2 vital valves built into the pump. A pressure relief valve, and a pressure compensated flow control valve. If you use a commercial type pump you will have to purchase, mount, and plumb up these 2 extra valves.

See comment above. These two are included in the pumps being considered. They are also duplicated in the Orbitrol valve as well. Being open center with a power beyond port, the Orbitrol only uses what it needs to steer(both pressure wise and flow). Everything else is bypassed straight back to the reservoir(via either the open center or power beyond port).

6. Don't forget that the larger the commercial pump flow, the larger the reservoir required. Rule of thumb is 3 x GPM for the reservoir size. This can be reduced down to 1 x GPM if you install an additional cooler. Dedicated power steering pumps use some internal trickery to get away with smaller reservoir sizes. They also use longer routing of the return lines to allow heat to dissipate prior to returning to filter and reservoir.

Most of these setups(off road hydro steering) run reservoirs sized at about 1 quart. Needless to say, they overheat and it causes issues. One of my first inclinations was that the cooling was way undersized. I am confident the 5 gallons of fluid will be more than enough for my needs. I am infrequently moving a (very) small ram compared to something like an excavator which needs to do it all day long with many large hydraulics loads. The way power steering pumps deal with excess is by internally recirculating fluid. It does cause heat when the systems are under high pressure. The Orbitrol constantly circulates fluid through the entire system, not just internally. Being that I am planning on a 5 gallon reservoir, there are very few places to install it. It is likely going near the back of the vehicle. The lines will be plenty long enough to cool the fluid. A couple heater cores will likely be employed to help cool as they are rated for much higher pressure than conventional radiators. System sizing also plays a huge role in heat generation. Many systems are sized too small and the restrictions cause excess heat. I am going bigger than required on everything, so comparatively, my system will be lower pressure and lower flow than I need.

7. Whatever you do, work out your actual flow calculations very carefully. Engine RPM range, dia of crankshaft pulley and dia of pump pulley and the displacement of the pump in cubic inches/rev (or cc/rev) should give you the right answers. You need enough flow at idle to slowly turn your steering, and not tooo much at high engine revs.

Already done, but the problem isn't in the numbers I get, it is matching it up to the configurations that work with the Orbitrols. My crank pulley is a 25% underdrive unit. With a 6.5" pump pulley, it gives me a ratio of .86 for rpms that the pump sees. My engine is putting out 550 horsepower. At 2,800rpm I am putting out what the stock VX puts out redlined. Pushing my numbers up to 5,000 rpm, I am only turning the pump at 4300rpm. Most regular vehicles seldom see 5,000 rpm, let alone most V-8's. For the very small amount of times the pump will see high rpms and the even smaller window of time it will be exposed to them, I think I'll be OK. Based on my gear calculations, at 3,000 rpm, I am hitting 110 MPH in 5th gear. The problem with these systems is we often need the most flow and pressure when we are going slowly and th least when we are driving fast. I have a PTO capable of driving a separate pump and I was considering that route, but it greatly complicates the steering circuit and seems like a compromise. I personally do not want much flow. In steering, flow equals steering responsiveness/speed. I would prefer a normal amount of turns lock to lock under normal conditions and a lower amount, but still precise while going slow in the rocks. It seems like it could be accomplished through either some Orbitrol trickery or by just throwing some check valves into the circuit to force the KRC pump to go into bypass mode while the high PSI, high flow PTO pump takes over.

That is probably enough for now.
If you need any help sorting through the options of the Orbitrol units give me a yell. Unless you have been especially trained in military driving techniques, avoid any orbitrol unit that will give you live feedback. Otherwise you will break your thumbs as the road wheel hits a rock and the steering wheel spins uncontrollably out of your hands.

I have actually been trained in special military driving techniques, and I can tell you a rig with running large tires and tight steering offroad will break your fingers off every bit as quick as a hydro unit.

I have been retired for a few years now, but still do some consulting work when I am dragged back for particular problems.

For reference, here is where I am getting a good portion of my information:

LINK