CBR Steering Pumps - OEM Applications?

[AgitatedPancake]

What’s the story on OEM CBR power steering pumps? I’ve been reading some cool steering tech from years back, but CBRs were relatively new to the scene. They seem like a pretty big go-to in the aftermarket these days, but who’s running some parts store CBRs?

Those old threads were saying like 2010-2012 V8 camaros and a few other models, but I’m sure that list has grown over the years.
I have the grand cherokee hydro fan TC pump (on my grand, but fan deleted), and I’m tired of it screaming above 2300rpms. Sounds like the cbr should physically bolt in the same spot with a different offset pulley, but probably need new pressure line and reservoir setup. Are they that good?

I'm also looking at the aftermarket offerings from PSC, Radial Dynamics, and the Scott Trimarco's gear pumps, but that's a last resort if I can't find any good tech on the latest cool OEM pumps.

 

['84 Bronco II]

It sounds like '16-'19 Duramax CBR pumps might be worth looking into. MtnYota put one on his rig, but hasn't tested it yet: https://irate4x4.com/ford/32894-explorer-5-0-ps-pump

There is also some good discussion over on IH8MUD

 

[Aisin]

From a quick search 2005 Chevy SSRs, 2005 Trail Blazers and the Camaros of course.

 

[Provience]

I'm also looking at the aftermarket offerings from PSC, Radial Dynamics, and the Scott Trimarco's gear pumps, but that's a last resort if I can't find any good tech on the latest cool OEM pumps.

radial dynamics sells the full line of PSC stuff which is nice and has a few of his own things as well with the reservoirs and such. As far as i'm aware, he never was able to get his own full custom pump up and running at anything close to a competitive price, but his modified CB-X 6GPM 1800PSI is where i'm heading for my junk.


what are you trying to power with it? you may not need that much flow or that much PSI, and that would be where the PSC options can be cheaper to toss in and run.

If you are just fighting screaming and have no issues with flow or pressure from your current pump doing work, why not add more fluid to the system with a bigger reservoir or adding in a cooler or checking lines to make sure you aren't starving it?

Scott makes some good stuff for using the gear pumps and those setups are certainly price competitive for what you can get out of them, but it really seems like they 'should' be setup with more flow control stuff than people use them with typically.

 

[RadialDynamics]

I'd be happy to chime in here with some insight from a manufacturer's perspective. The posts and links above reference some of the OEM applications where CBR pumps are used and yes, the aftermarket CBR's all begin life as one of these OEM pumps. For the most part, what sets the aftermarket pumps apart is different inlet and outlet fittings, modification of the pump housing to accept the new inlet fitting, and adjustment of the flow control and pressure relief valving.

Sure, you could get an OEM pump and modify it yourself, there are plenty of resourceful people on here with the capabilities to do so at home. There are also a number of how-to articles floating around the internet that show how to modify the flow and pressure settings in steering pumps but I recommend anybody attempting this themselves to proceed with EXTREME caution. It takes very little adjustment of the pressure relief valving (shim stack on the flow control spool, for those that are familiar) to end up with a pump that has dangerously high relief pressure. Overpressure can not only damage the pump internals but can also split pump housings and burst hoses or fittings which I have seen happen. Spraying fluid onto a hot exhaust and catching fire is one risk but also hydraulic injuries such as fluid injection are no joke which is why I take this stuff very seriously.

To start with a new-manufactured genuine pump will likely be between $140-$190 depending on exactly which pump model you get. I discourage reman pumps because there is no telling what you will actually end up with. So for an extra hundred or few hundred dollars, you not only get the modifications already taken care of for you but you also get the piece of mind that the pressure relief setting has been adjusted and tested to be as stated.

That's just the safety reason for looking to the aftermarket. Digging deeper into the pump specifics, I see that MtnYota experienced one of the biggest issues that I have with the CBR... the fact that the body (and bore of the flow control valve) is aluminum so the flow control spool, which changes position constantly based on engine speed, is prone to stick with the pump open to bypass. This is the reason I try to avoid any aluminum-bodied steering pumps. Cast iron pumps are more wear resistant in this bore and are therefore less prone to getting a sticky valve (keep in mind the clearance between the bore ID and spool OD is less than 0.0005").

The CBR pumps also have another issue in my eyes, the fact that the shaft is supported with a bushing rather than a bearing which is not as well suited for handling the increased side load on the shaft from the increased relief pressure compared to OEM applications. For every increase in pressure relief setting, there is a directly proportional increase in consumed HP which means a proportional increase in side load from the serpentine belt.

The benefit to CB/CBR pumps is the fact that they fit in place of a TC pump but feature a larger internal displacement and therefore you can get more flow out of them for a given drive speed. This makes the biggest impact at idle and low RPM operation. The way I see it, the Saginaw CB pump is an excellent compromise in displacement volume and physical packaging.

To make up for the shortcomings with the CBR, I started offering my own CB-X line of pumps earlier this year which is built on a cast iron Saginaw CB. In addition to the benefit of reduced wear in the flow control valve, the body of my CB-X is bored out to support the replacement chromoly shaft with a set of roller bearings instead of the OEM bushing. I stock two standard variations, both regulated to 6 GPM max flow but with different pressure relief settings. The 1600 PSI version features a standard 0.664" diameter shaft to take press fit pulleys for your standard TC/CB/CBR pumps. My higher pressure 1800 PSI version has a 1/8" keyway milled into the shaft and I offer reaming and broaching of any available press fit pulleys to mate to this pump, eliminating the chance of pulley slippage. Remember, higher pressure means higher consumed HP making pulley slippage more likely to occur.

Getting back to the OP's question, if your pump is screaming at high RPM, this could possibly either be a worn pump and/or could also be caused by inadequate feed hose/reservoir design. Simply swapping in a larger displacement or higher flow pump will not ultimately solve that problem without also taking a look at the rest of your system and ensuring that everything is properly sized to handle your maximum pump discharge flow rate.

 

[Weasel]

yes this place is starting to get cooking, love it. Thanks for the info been watching the few youtube vids that pop up every so often and love the products your doing.

 

[RadialDynamics]

Much appreciated! It's been a while since I have logged onto any forums myself but I really hope that this place spurs a revival because there is so much good tech to share and everything just gets lost so quickly on social.

 

[Aisin]

So the next question is where do the cast iron pumps come from?

 

[RadialDynamics]

The cast iron CB pumps came in a variety of GM vehicles from the mid 90's to late 2000's (maybe even later). Some of the vehicles include the 97-02 Chevy Malibu, 97-05 Chevy Venture, 02-07 Buick Rendezvous, just to name a few. I'm sure you can find many more. Every OEM pump might have slightly different pressure and flow settings depending on exactly which vehicle it was intended for. I couldn't tell you the break down model by model but these cast iron CB pumps will still have a bushing shaft support and require modification to the housing and valving in addition to new fittings in order to match the fit and performance of an aftermarket pump.

 

['84 Bronco II]

The cast iron CB pumps came in a variety of GM vehicles from the mid 90's to late 2000's (maybe even later). Some of the vehicles include the 97-02 Chevy Malibu, 97-05 Chevy Venture, 02-07 Buick Rendezvous, just to name a few. I'm sure you can find many more. Every OEM pump might have slightly different pressure and flow settings depending on exactly which vehicle it was intended for. I couldn't tell you the break down model by model but these cast iron CB pumps will still have a bushing shaft support and require modification to the housing and valving in addition to new fittings in order to match the fit and performance of an aftermarket pump.

Thanks for all the good tech

It seems like for us cheap bastards, diesel application pumps ought to be the best bet since they should have the highest pressure and flow demands due to their weight and factory hydroboost brakes. Any idea what the rough difference in flow and pressure would be between an OEM CB and CBR pump? I remember seeing a chart for different OEM applications a while back, but haven't seen anything like that for the newer pumps.


EDIT: Here is a thread with another guy using a '17 Chevy 2500 6.0L Pump

 

[Aisin]

Awesome. Thanks for taking the time to share your knowledge. As 84 Bronco said, most of us are cheap fucks.

 

[AgitatedPancake]

Oh man, thank you all for the responses so far, I may have to do a few responses. And thanks a ton Eric, I really enjoy the deep dive into tech subjects like this. Actually I was talking to Kyle with the Dakota yesterday on the topic, and he couldn't express enough how helpful you've been in getting the kinks worked out in his steering system. So all of the modern CBRs are aluminum housing, then the earlier CBs you noted have the iron housing, but all CB/CBR come with bushings instead of bearings for shaft support, that's great info. On some recent reading I was doing, some folks also noted that the way the OEM oriented the oil channel in those bushings to avoid seeing belt tension load depending on how the accessories were configured on each individual stock engine arrangement, so aftermarkets just place it wherever they want and sell it for multiple applications. So there's a chance any custom application could be loading the bushings directly over the oil channel and create accelerated wear. Don't know how much truth there is to that as i don't have bushing pump experience yet, but found the concept interesting.

I knew the spool valve was tight in the bore, but didn't realize the tolerances were that tight. I've torn apart a handful of steering pumps (actually took apart one of my old TCs last night), but haven't done too much modifying besides drilling the relief valve hole to a larger diameter, and messed with pressure relief shim springs a bit. I've seen where people have removed them all, and even added shim washers under the spring and cut the stud down a bit which is way more than I would ever need. Actually I've got a ton of working hydraulic surface area in my system so I don't need extremely high PSI to achieve what I want, I just need to flow to fill it all (which is currently bottlenecked by a stock servo valve integrated into the PS box, but unless it's causing my pump issues that's something I'd like to approach later on down the line.

I've got one nitty gritty question that i could use some help on, to help complete my understanding of the pumps bypass operation. I'm linking a KRC article that has been a great reference to the finer details, and I'll be using a pic from it in reference below. So I understand the flow path of the fluid from the high pressure side around the base of the pressure fitting through that small passage to the back of the spool valve where the pressure relief valve is integrated internally. It makes sense how pressure can overcome the spring pressure on the back of the sealing ball bearing at a certain pressure, so adjusting spring pressure adjusts relief pressure. What I haven't fully wrapped my head around is the movement of the spool valve itself for controlling flow. With it being pressurized from both sides via that small connecting side port, it seems like it would be somewhat neutral and not prone to shifting one way or the other. Unless that small diameter port pressurizing the back creates enough of a pressure differential to overcome spring pressure and open the flow control? So in this picture, Figure 6 shows the high pressure relief bypassing, but the flow control valve shut. Figure 7 shows the high pressure relief bypassing, but the flow control valve open. Just wrapping my head around the action of that flow control valve and the fluid path/pressure differential at work has been making my head hurt

 

[Sterlingfire]

You are correct, it is a pressure differential type of valve. The size of the port on each side is what controls how much pressure it takes to open it.
We use these in dry valves for fire sprinklers. Our clappers (as we call them) are a 6:1 pressure differential. That means it takes 6 psi to push past 1 psi of static pressure. You could figure out the differential by micing the port on each side and a few calculations.

 

[Slander]

Subbed!

 

[RadialDynamics]

Thanks for all the good tech

It seems like for us cheap bastards, diesel application pumps ought to be the best bet since they should have the highest pressure and flow demands due to their weight and factory hydroboost brakes. Any idea what the rough difference in flow and pressure would be between an OEM CB and CBR pump? I remember seeing a chart for different OEM applications a while back, but haven't seen anything like that for the newer pumps.


EDIT: Here is a thread with another guy using a '17 Chevy 2500 6.0L Pump

Unfortunately, I do not know exactly how the regulated flow rate and relief pressure settings compare between OEM models. The only pump specs that I can say with certainty are for the pumps that I offer so when it comes to selecting an OEM pump, that's a decision I have to leave up to you.

As for the KRC drawings, I can see how this is confusing and the function of flow control is probably one of the most misunderstood topics that I come across relating to steering pumps. I just recently cut apart a pump casting so that I can explain this subject more clearly in a future post but I will do my best to explain here. During normal operation, the flow control spool sees a higher pressure on the side facing the pump outlet than on the backside. The difference in pressure comes from the pump outlet fitting itself, not the pilot port. When fluid is exiting the pump body and flowing through the orifice in the pump outlet fitting, it experiences a pressure drop. This pressure drop is related to flow rate and nothing else.

As an example (just pulling numbers out of thin air right now), let's say that you are holding constant throttle position and the pump is moving 5 GPM with a 50 PSI pressure drop through the orifice. If you are not actively steering, the pressure in your system is essentially 0 PSI so the pressure in the high pressure side of the pump body is at 50 PSI. If you begin to turn and the system goes up to 1000 PSI, now the pressure inside the pump is at 1050 PSI. That flow control spool sees internal pump pressure on the side facing the outlet and the pilot port connects the back side of the spool to the system pressure downstream of the outlet orifice (minus 50 PSI in this example). That 50 PSI differential is what causes the spool to compress the spring and move away from the outlet fitting. Higher flow (i.e. higher RPM) means higher pressure differential which causes the spool to depress deeper into the bore. Eventually, it moves far enough that fluid starts to bypass right back into the low pressure side of the pump.

The great part about this is that the flow control spool only sees the pressure differential across the outlet fitting orifice so it maintains a controlled flow rate regardless of fluctuations in system pressure. This is called a "pressure compensated flow control valve". One of the most common myths I see is that the orifice in the outlet fitting is a major cause of heat because it "restricts" the flow and forces fluid to bypass which is incorrect. It is simply creating a relatively minor pressure differential to control valve position. Drilling out the orifice in the outlet fitting does little other than change the pressure drop curve and thereby increase the flow rate (and hence, RPM) at which enough differential pressure is created to open up the bypass. It does not change idle/low RPM flow rate.

When it comes to the shaft bushings, the oil groove is actually a spiral. Here is a CBR that I just dissected for a customer yesterday. While it could have a minor effect, I would not be too overly concerned about oil groove orientation of an installed pump.

 

[AgitatedPancake]

Actually that is crystal clear to me now, thank you a ton for that. Looking at the output fitting now, the tiny holes above the threads on the fitting feed that pilot port to the back of the spool valve. Not that the threads are fully liquid tight, just create enough restriction for any minor bypass be irrelevant for the intended purpose. I was trying to grasp how those holes came into play, and that makes perfect sense now. They're right at the top of the outlet restriction, so they see that pressure drop and feed that to the back of the flow control valve.

So these grand cherokee hydro fan pumps are really interesting in that regard. They have an absolutely massive primary orofice diameter here. Greater than 1/4". So they have the ability to send tons of volume out to the fan before reaching a volume that causes it to bypass. Now what's really interesting is what I've encountered with some of the aftermarket ones, and I'd be curious how significant this difference is. So I have 6 of these fittings on a bench right now. The top left two are zinc coated OEM hydro fan fittings (with an unusual/not adaptable 20mm oring fitting). The right hand two are hydro fan fittings from reman pumps, look to be stainless. The bottom left two are standard non hydro fan fittings with your common 16mm oring fitting.

Standard non hydro fan TC pump port diameter (~1/8" iirc):

Hydro fan orofice diameter:

Now the part I find interesting is in the below picture. Left to right: The left is an OEM hydro fan fitting, large diameter primary port but *4* small orofices for sensing pressure drop. The middle one is an a reman stainless hydro fan fitting, same large primary port diameter, but single pressure drop orofice. The right one is a factory non hydro TC pump fitting, with a single pressure drop orofice.

 

[Provience]

AgitatedPancake i'm a jeep noob, what the heck is this "grand cherokee hydraulic fan pump" that you are speaking of?

do you mean vane style pump?

 

[AgitatedPancake]

the 2001-2004 V8 Grand Cherokees (WJ's) had a cooling fan that was hydraulically powered, run off the steering pump. So the pumps (which look pretty stock externally) are ported from the factory and have a few other features for extremely high flow volume. In the stock application, the high pressure output line is 1/2" to the fan, which has it's own 1/2" return line to the reservoir. The fan then has a high pressure 3/8" output to the steering box, which has it's own 3/8" return to the reservoir. So in that regard, the plumbing of the whole system is set up somewhat similar to hydroboost. I have a 2001 grand cherokee, but I deleted the fan. People have liked this pump for being a sweet factory option, but it has been a crapshoot with quite a few people having noise problems. I'm one of them, as my pump has been screaming above 2500 RPMs. As of tonight that may be cured with a smaller diameter orofice in the pressure drop fitting to bypass at a lower fluid volume and trying the other reservoir return barb, but we'll see with time.

I don't have pics of standard port sizes in TC pumps, but I did take some pics of the large port diameters on this pump I just tore apart last night.

Here's looking into the pump inlet from the res, these openings are all oversized

The same ports, looking from inside the pump. The cylindrical hole facing the camera is the bypass port from the flow and pressure relief valving, that recirculates right into where the reservoir feeds

And this top right slot is the pressure out port from the pump:

And it has a cam ring stamped with a double diamond, which i believe indicates the largest displacement TC pump that they make?

So *if* I can get the pump happy (which I think I may be able to now with my new understanding of how things work), it's supposed to be a halfway decent option.

 

[arse_sidewards]

AgitatedPancake i'm a jeep noob, what the heck is this "grand cherokee hydraulic fan pump" that you are speaking of?

do you mean vane style pump?

Certain GCs got a hydraulically driven radiator fan. Like the kind of thing you see on some city buses, but smaller and shittier. These GCs used a different power steering pump. Hence the "hydraulic fan pump".

Edit: beat my by one minute.

 

[RadialDynamics]

Regarding the picture of the outlet fittings with different numbers of pilot orifices, the number of orifices does not really have any effect on operation. They are not "sensing" the pressure drop, they are simply opening up fluid communication between the discharge side of the outlet fitting and the pilot passageways in the pump housing. Since these orifices are drilled into a groove in the OD of the outlet fitting, it does not really matter where the orifice (or multiple orifices) end up in orientation relative to the pilot passageway in the housing.

 

[HYDRODYNAMIC]

OEM car and truck design requirements are not the same as off road requirements. When was the last time you had the wheel of your Camaro at full lock and or up against the curb and bouncing off the rev limiter?
Putting a flow control and relief valve together into a small pump housing is great for packaging, eliminating hoses and extra parts, and service. It is horrible at feeding the pump with clean air free cool oil. Instead of trying to figure out how to modify all the different flow controls, figure out how to delete them.
Use a reservoir that keeps air out of the oil. Use large suction lines. Use large pressure lines. Use an external relief valve. Use an effective filter. Send all the hot oil to an effective cooler.
An OEM built in flow control relief valve dumps oil right out of the vanes back into the vanes, yes it might take some turns and passage ways, but it is bypassing a filter, cooler, and way to get the air out. Throw in some air, some hot oil, and some debris and you have exponential wear in the pump as it can not get those things out.

Regardless of if you want to run an external relief or internal relief or external flow control or internal flow control. STOP saying this or that pump is a (blah blah) GPM pump. Pumps have a displacement per revolution. The speed of the pump directly determines the flow of the pump. The speed of the pump is determined by all the active pulley sizes and engine rpm. If you are using a flow control then the pump is regurgitating some of the GPM before it exits the housing where it can be measured. So an OEM pump without a flow control will put out more GPM than one with one.

If you want to run an external relief valve make sure it can handle the full flow of the pump at max output and adjust the relief for max pressure at full flow meaning, go to full lock and full rpm then set the relief pressure. Depending upon the relief you are using it might start to open at a lower pressure and climb as the flow increases. Do not try to set the relief until the plumbing circuit has had a change to work out all the air out the system. Also keep an eye on the temps to make sure the cooler is keeping up with the heat generated.

 

[rockdog57]

I’ll second the air in the system and oil volume.
You need volume to get the air out and allow your fluid to cool down. I did this on my rig with a big cooler and added volume to the housing. It solved my pump squealing problems.

 

[Fwjeep]

OEM car and truck design requirements are not the same as off road requirements. When was the last time you had the wheel of your Camaro at full lock and or up against the curb and bouncing off the rev limiter?
Putting a flow control and relief valve together into a small pump housing is great for packaging, eliminating hoses and extra parts, and service. It is horrible at feeding the pump with clean air free cool oil. Instead of trying to figure out how to modify all the different flow controls, figure out how to delete them.
Use a reservoir that keeps air out of the oil. Use large suction lines. Use large pressure lines. Use an external relief valve. Use an effective filter. Send all the hot oil to an effective cooler.
An OEM built in flow control relief valve dumps oil right out of the vanes back into the vanes, yes it might take some turns and passage ways, but it is bypassing a filter, cooler, and way to get the air out. Throw in some air, some hot oil, and some debris and you have exponential wear in the pump as it can not get those things out.

Regardless of if you want to run an external relief or internal relief or external flow control or internal flow control. STOP saying this or that pump is a (blah blah) GPM pump. Pumps have a displacement per revolution. The speed of the pump directly determines the flow of the pump. The speed of the pump is determined by all the active pulley sizes and engine rpm. If you are using a flow control then the pump is regurgitating some of the GPM before it exits the housing where it can be measured. So an OEM pump without a flow control will put out more GPM than one with one.

If you want to run an external relief valve make sure it can handle the full flow of the pump at max output and adjust the relief for max pressure at full flow meaning, go to full lock and full rpm then set the relief pressure. Depending upon the relief you are using it might start to open at a lower pressure and climb as the flow increases. Do not try to set the relief until the plumbing circuit has had a change to work out all the air out the system. Also keep an eye on the temps to make sure the cooler is keeping up with the heat generated.

What are you using for flow control? External pressure relief sized for the gpm, absolutely. Also your orbital needs to push that much without much restriction, at rpm. At full get, making near 17gpm. certainly a steering box will not flow that much. Is the spool removed from your pump, and a solid plug pushed in, or a new housing

as for the grand Cherokee pump, I have lots of them here,
I believe you need to understand what the spool valves on the fan do to distribute flow to the steering box. I’m going to assume it is some sort of priority flow control.

 

[Provience]

What are you using for flow control? External pressure relief sized for the gpm, absolutely. Also your orbital needs to push that much without much restriction, at rpm. At full get, making near 17gpm. certainly a steering box will not flow that much. Is the spool removed from your pump, and a solid plug pushed in, or a new housing

as for the grand Cherokee pump, I have lots of them here,
I believe you need to understand what the spool valves on the fan do to distribute flow to the steering box. I’m going to assume it is some sort of priority flow control.

it's probably not on a priority control, for as intermittent as steering flow demand is and as consistent as a fan demand would be, i could see an OEM saying "fuck it, send it all to the fan and then pass through whatever remains to the steering"

guess i should go look for a diagram and find out

edit: here is a "hose diagram" for the fan.

Here is an actual picture

02 2002 Jeep Grand Cherokee Power Steering Hose - Steering - API, CARQUEST, Edelmann, Gates, Mopar, Omega, Sunsong, From Pump To Hydraulic Fan Motor, Gear To Filter, Gear To Pump - PartsGeek

and according to the hose list, routes pressure from pump to fan via far right hose, then pressure from fan to steering gear via middle hose, far left hose appears to be drain from fan to the bottom of the reservoir?

and the steering gear drains into the cooler and the cooler drains into the back of the reservoir

MasterPro Power Steering Pump - Remanufactured 73328104 | O'Reilly Auto Parts

 

[HYDRODYNAMIC]

I am not using an internal flow control.
I am using the PSC CBR XR RACE pump in 11.3cc/rev = .689ci/rev
I have not taken it apart yet but it has nothing where the normal flow control would go. It is straight through. It has a billet housing. I don't know if they use this housing for bypassed versions if so I would assume they leave out a porting path from pressure to return for the RACE version.
The pulley size is close to the crank pulley guessing 1:1, if over or under driven, flow will change
at 6000 rpm 17.89 GPM
at 4000 rpm 11.93 GPM
at 2000 rpm 5.97 GPM = 1 second lock to lock if the wheel could turn fast enough, 2.64 turns
at 1000 rpm 2.98 GPM

My old buggy ran a 1.0ci/rev gear pump through a D05 direction control valve and then through the PSC orbital
at 5000 rpm 21.64 GPM
I am sure it generated some heat, but the cooler took care of it no problem. The relief valve could full flow and not over pressurize.

Some believe a flow control to be a way to not build heat. That is not the case for the most part. It is only good for slowing something down.
Say the pump is at 10 gpm and you only want 6 gpm so you use a flow control to send anything over 6 back to tank. The orbital will only see 6 gpm. The pump will still see the full 10 gpm at whatever pressure is needed by the orbital which could be the relief pressure at 1800 PSI.

For example you run a steering gear which is highly restrictive and use a flow control to slow the flow through the gear. The gear is flowing 4 gpm and the bypass is flowing 6 gpm and with no use the pump is seeing 500 PSI at 4000 rpm. As soon as you go to turn the wheel the pressure goes up and the pump has to send all 10 gal at 1500 psi working pressure. 4 gpm through the gear at 1500 psi and 6 gpm through the flow control at 1500 psi to the tank.
The benefit to running the flow control is that if you do not turn often or under much load you can reduce heat by not sending all the oil through a restrictive gear or orbital or valve. If the gear has 500 psi of restriction at 5 gpm then doubling the flow to 10 gpm could make 1000 psi of restriction. So the pump seeing 5 gpm at 500 psi through the gear plus 5 gpm through the flow control to tank is 10 gpm at 500 psi which is better than everything through the gear at 10 gpm at 1000 psi.

If the orbital is seeing turns and pressure all the time there is not much of a benefit for a flow control with a well flowing circuit. If you do not want to have a more responsive steering feel or have a restrictive part in the circuit an external flow control might help. Do not confuse an external flow control for an internal as internal does not get the hot oil out of the pump compared to an external which sends it to a cooler and filter before the pump sees it again.

 

[HYDRODYNAMIC]

I’ll second the air in the system and oil volume.
You need volume to get the air out and allow your fluid to cool down. I did this on my rig with a big cooler and added volume to the housing. It solved my pump squealing problems.

Big reservoirs are not as important as a properly design cooler and air removal reservoir design. When I first build my hydraulic buggy it had a 20 gpm tank because that's what the rule of thumb was. When I was done modifying it, it was down to a 1 gallon reservoir. For a system flowing over 40 gpm the reservoir was more than enough. Its only job was to expand and contract and aid in filling and de-aeration. The reservoir only had one line which was both the inlet and outlet. The plumbing circuit ran from the pump through the coolers and filters and right back into the suction in term called supercharging. Once the air was worked up and out to the high point in the system it was trapped and removed. With no air available to mix with the oil there was no need to de-aerate the oil. Reservoirs can only cool a small percentage compared to a dedicated cooler. The plumbing, baffling, catch can, and fill methods also have a much bigger impact on de-aerating and air oil mixing than the reservoir size.

 

[HYDRODYNAMIC]

it's probably not on a priority control, for as intermittent as steering flow demand is and as consistent as a fan demand would be, i could see an OEM saying "fuck it, send it all to the fan and then pass through whatever remains to the steering"

and according to the hose list, routes pressure from pump to fan via far right hose, then pressure from fan to steering gear via middle hose, far left hose appears to be drain from fan to the bottom of the reservoir?

and the steering gear drains into the cooler and the cooler drains into the back of the reservoir

There is a good chance the fan has an electronic variable rate flow control that ramps up and down for fan speed vs 100% on or off. The addition of the drain and solenoid on the fan motor/valve is a sign that the oil is returning to the resvoie instead of sending whatever it doesnt use to the steering gear. People would be complainging if the steering gear felt like it had more or less power as the fan cycled on and off. If anything the gear would get priority flow and the fan would be second. It is easier for OEM to make one special all in one motor/valve than a different pump or gear.

 

[Provience]

I am not using a flow control.
I am using the PSC CBR XR RACE pump in 11.3cc/rev = .689ci/rev
I have not taken it apart yet but it has nothing where the normal flow control would go. It is straight through. It has a billet housing. I don't know if they use this housing for bypassed versions if so I would assume they leave out a porting path from pressure to return for the RACE version.
The pulley size is close to the crank pulley guessing 1:1, if over or under driven, flow will change
at 6000 rpm 17.89 GPM
at 4000 rpm 11.93 GPM
at 2000 rpm 5.97 GPM = 1 second lock to lock if the wheel could turn fast enough, 2.64 turns
at 1000 rpm 2.98 GPM

My old buggy ran a 1.0ci/rev gear pump through a D05 direction control valve and then through the PSC orbital
at 5000 rpm 21.64 GPM
I am sure it generated some heat, but the cooler took care of it no problem. The relief valve could full flow and not over pressurize.

Some believe a flow control to be a way to not build heat. That is not the case for the most part. It is only good for slowing something down.
Say the pump is at 10 gpm and you only want 6 gpm so you use a flow control to send anything over 6 back to tank. The orbital will only see 6 gpm. The pump will still see the full 10 gpm at whatever pressure is needed by the orbital which could be the relief pressure at 1800 PSI.

For example you run a steering gear which is highly restrictive and use a flow control to slow the flow through the gear. The gear is flowing 4 gpm and the bypass is flowing 6 gpm and with no use the pump is seeing 500 PSI at 4000 rpm. As soon as you go to turn the wheel the pressure goes up and the pump has to send all 10 gal at 1500 psi working pressure. 4 gpm through the gear at 1500 psi and 6 gpm through the flow control at 1500 psi to the tank.
The benefit to running the flow control is that if you do not turn often or under much load you can reduce heat by not sending all the oil through a restrictive gear or orbital or valve. If the gear has 500 psi of restriction at 5 gpm then doubling the flow to 10 gpm could make 1000 psi of restriction. So the pump seeing 5 gpm at 500 psi through the gear plus 5 gpm through the flow control to tank is 10 gpm at 500 psi which is better than everything through the gear at 10 gpm at 1000 psi.

If the orbital is seeing turns and pressure all the time there is not much of a benefit for a flow control with a well flowing circuit. If you do not want to have a more responsive steering feel or have a restrictive part in the circuit an external flow control might help. Do not confuse an external flow control for an internal as internal does not get the hot oil out of the pump compared to an external which sends it to a cooler and filter before the pump sees it again.

to expand on the case for flow control:

if 5.97 gpm is giving you more flow than your steering could hope to use, then you are only hurting yourself by running everything else, up to 18 gpm, through the steering valve.

Is it enough to make your steering noticeably different at higher flow? maybe, maybe not. If it does NOT make a difference to how your steering reacts, then odds are very good that you are at the point of restriction and the extra flow is just adding heat. If it DOES make a difference, then at least you aren't adding a restriction, but you will have a different steering feel through the range.

By running the full flow through the steering valve, you are very likely adding a couple to several hundred PSI needlessly, the steering itself may demand a very low pressure even if you are turning often. the majority of the time the system will be under the relief pressure, save some HP.

because you are not adding the extra pressure from running high flow through the steering valve, you are able to make better use of the regulated pressure the valve does see, so your same relief pressure will net you more work, in addition to being more consistent and lower drag and cooler.

I do agree that external is better than internal, but internal is significantly cheaper

 

[Provience]

There is a good chance the fan has an electronic variable rate flow control that ramps up and down for fan speed vs 100% on or off. The addition of the drain and solenoid on the fan motor/valve is a sign that the oil is returning to the resvoie instead of sending whatever it doesnt use to the steering gear. People would be complainging if the steering gear felt like it had more or less power as the fan cycled on and off. If anything the gear would get priority flow and the fan would be second. It is easier for OEM to make one special all in one motor/valve than a different pump or gear.

good point

 

[HYDRODYNAMIC]

to expand on the case for flow control:

if 5.97 gpm is giving you more flow than your steering could hope to use, then you are only hurting yourself by running everything else, up to 18 gpm, through the steering valve.
The benefit is to run a larger pump so the low rpm flow is up and the high rpm is bypassing

Is it enough to make your steering noticeably different at higher flow? maybe, maybe not. If it does NOT make a difference to how your steering reacts, then odds are very good that you are at the point of restriction and the extra flow is just adding heat. If it DOES make a difference, then at least you aren't adding a restriction, but you will have a different steering feel through the range.
Low flow at low rpm can stop you from turning which is a big deal, high speed being too sensitive is driver correctable.

By running the full flow through the steering valve, you are very likely adding a couple to several hundred PSI needlessly, the steering itself may demand a very low pressure even if you are turning often. the majority of the time the system will be under the relief pressure, save some HP.
The system will not go over relief unless at lock or tires are stuck.
Running oil through an extra flow control might add just as much restriction and needless pressure loss. Nothing works for free.

because you are not adding the extra pressure from running high flow through the steering valve, you are able to make better use of the regulated pressure the valve does see, so your same relief pressure will net you more work, in addition to being more consistent and lower drag and cooler.
This is true in theory.

I do agree that external is better than internal, but internal is significantly cheaper
Only cheaper until the first pump chokes on its own vomit and dies. Then you might as well have done it correctly the first time.

RED