Power Steering Pump Tech

#1
This is copied from patooyee from pirate, I thought it was really good tech.


patooyee said:
First of all, this is going to be LONG. If you don’t like me, my obsession with tech, think I am a post whore, or are just illiterate and don’t like to read, just stop. NO ONE IS FORCING YOU TO READ THIS so you only have yourself to blame if you do so.

Many people I know seem to have PS Pump issues. Whether they lack steering power, steering speed, or pump longevity, we are seldom completely happy. Oftentimes improvements in one aspect result in worsening another. This has been my case for many years. I have used stock OEM pumps that seem to last a long time but don’t have the power or speed that I want. I have purchased many aftermarket pumps that claim to solve my issues with the OEM units, some of which have. But it seems like they come with a reduced lifespan in exchange. As of the writing of this article I have in my shop 3 aftermarket “P” style pumps, 3 OEM “P” pumps, 2 “CB” style pumps and a “TC” style pump. Long ago I vowed to stop spending money on aftermarket pumps that will supposedly solve my issues until I learn more about them. Questions flow through my head that must be answered such as:

What are the differences between the 3 popular styles of pumps?
Which style is most suited to our needs?
What is causing the demise of my pumps?
What are the aftermarket manufacturers doing to gain performance?
Can I perform modifications on my own to improve performance similar to what the aftermarket companies do?

Not all of these questions have I answered yet. But I am on my way to gaining the knowledge required to do so and I figured I would share what I know so far and see if people can give me some more input. Ls1toyota is also interested in this issue and has been working with me on this.

This thread will focus on the internal workings of the vane pumping mechanisms themselves and not so much the valving that exists inside the pump. To learn more about that you can see this thread: http://www.pirate4x4.com/forum/showthread.php?t=970103

I’ve always found that truly understanding the way something works means starting at the most elemental beginning and following it forth from there. So that is what I decided to do with a TC, CB, and 2 P style pumps. I will show you disassembled pics of all 4 pumps’ internals and follow the path of fluid from inlet to outlet. I will start with the TC, move onto the CB and end with the two P-Pumps. One will be a stock pump while the other will be an aftermarket unit. Names of manufacturers will not be mentioned as it is not the intent of this thread to give away any one specific company’s secrets or rag on any of them. I merely seek to gain more knowledge by sharing what I have with others.

In all of these photos, yellow indicates low pressure intake flow from reservoir to pump. Red indicates high pressure flow. Pink indicates valving pilot flow. To learn more about valving see the above linked thread.
 
#2
tc%20out%20(Medium).jpg

In the above photo fluid begins entering the pump through the large intake port at the yellow arrow. It ends its journey through the pump through the output orifice indicated by the red arrow. A pressure compensated flow control valve is operated via porting that is machined into the case of the pump. You can see where the port is drilled and then capped during manufacture from the side of the pump indicated by the pink arrow. The pilot flow path is indicated in pink going from the output fitting to the flow valve behind it. The following photo shows the view from the front of the pump where a second hole is bored to route the pilot fluid back in toward the flow valve. You can also see the front shaft bearing which is one of the two bearings that make TC pumps unique. All of the other pumps discussed in this thread are only supported by lubricated bronze bushings. Being that the TC pump shaft is supported front and rear by roller bearings it is generally believed that it can handle higher rpm’s than the others. I have evidence to both confirm and dispute this which I will discuss later.

tc%20case%20front%20(Medium).jpg

tc%20case%20(Medium).jpg


Looking at the bare case from inside you can see the other end of the external ports. The pink dot indicates the difficult-to-see port where pressurized fluid is bypassed back into the low pressure side of the pump by the flow valve to relieve system pressure. It is this pressure compensated flow relief that prevents hoses from blowing out during pressure spikes, similar to what occur when we nail our tires against immovable objects at full throttle.

The following is a diagram that Ls1toyota provided for our reference. It explains the basic workings of a vane pump which you can refer back to as I continue:

vane%20pump.jpg

tc%20iso2%20(Medium).jpg

Here you can see the TC Pump’s cam pack removed. From left to right you see the back plate, the cam ring, the front plate, and the shaft. Fluid comes in the intake orifice and fills the body of the pump where it is then sucked into the inlet ports shown here. The o-ring you see seals inside a machined bevel in the pump body thereby sealing the low pressure zone (back of the pump housing) from the high pressure zone in the front.

tc%20iso1%20(Medium).jpg

Stripping away the internals one by one, this is a pic without the back plate on. Again, you can see an intake port only this time the vane rotor and cam ring are exposed. The vane rotor is splined to the pump shaft and rotates via the belt and pulley on the front of the pump. The vane rotor is the one and only internal component of the pump that spins. As it does so centripetal force causes the vanes to slide out of their grooves and come into contact with the inside of the cam ring. This is not the only force that causes them to do so though. As they create pressure fluid is forced through the oblong passages seen on the face of the cam ring from the front of the pump all the way to the back plate where it is then routed back down to the small holes you see at the back of the slots that the vanes are in. This not only helps to lubricate the vanes but also forces the vane outwards to keep them from being forced back in by the pressurize fluid that they are moving.

tc%20intake%20back%20(Medium).jpg

This is a photo of the back of the cam assembly without the back plate on it. Held up to the light you can see how the vanes follow the contour of the cam ring, forcing pressurized fluid out of the ports toward the front of the pump. The following photo is just a picture of the same component from the opposite side.

tc%20intake%20front%20(Medium).jpg

Another pic of the whole assembly from the front side, showing where the pressurized fluid exits toward the front:

tc%20iso3%20(Medium).jpg

Below is a photo of the front of the back plate. You can see the high pressure lubrication pathways and also the intake ports. The back plate seals against an o-ring in the back of the pump housing and fluid pressure at the front of the pump forces the entire cam assembly back against this back plate which then is stopped by the large c-ring that rests in the groove of the housing. Again, you can see the roller bearing that makes the TC unique. The TC is also unique in that it is the only pump that uses the back plate as the actual exterior of the pump also. This means that instead of all the pump’s pressure coming to rest against a thin piece of stamped steel, like all the other pumps, it comes to rest at a sturdy, thick piece of cast steel. This may mean that the TC has the ability to build more pressure than the other pumps but the casting is very thin in the middle. I accidentally shattered my back plate there while working on it. This may negate what would seemingly be a very sturdy barrier. I don’t know …

tc%20back%20plate%20(Medium).jpg

Right here would be a good place to put a pic of the back side of the front plate if I had one. But somehow I managed to not get that. If it was here though it would more fully describe how the vanes get oiled. I guess for the argument’s sake though you’ll just have to trust that they do get high pressure lubrication. :(
 
#3
The CB pump is very similar externally to the TC and therefore some pics may seem redundant. Internally achieves hydraulic pressure the same way too. However, the internal plumbing is slightly different. I will discuss that shortly …

Fluid goes in the intake. Please excuse my ghetto-fabulous –AN fitting that I rigged up. It’s not pretty but it works. Fluid exits the output orifice and you can see the pilot pathway as well as where the pilot pathway is machined and then capped during manufacture.

cb%20pilot%20(Medium).jpg

A different angle looking into the outlet fitting:

cb%20out%20(Medium).jpg

Looking into the inside of the empty cast housing you see where intake fluid comes in as well as pilot fluid during pressure relief. The CB is unique in that it has the pressure chamber separated from the rest of the pump via a cast wall. This means that, while the TC used fluid pressure to force the cam assembly BACK toward the back plate, the CB diverts pressure from the front of the pump to the back between the rear bulkhead and the back plate to force the cam assembly FORWARDS. The reason this is important will become clearer soon.

cb%20case%20(Medium).jpg

Instead of DISASSEMBLING the CB part by part like we did the TC we are going to ASSEBMLE it part by part for explanation this time. Below you can see how the front plate holds the vane rotor up off the dividing wall and takes fluid into the assembly through the voids created by the shape of the the plate. Pressurized fluid will then exit through the holes in red. Pressurized fluid is not allowed out of the front cavity backwards past the front plate because there is also hydraulic pressure forcing the front plate down against the machined flat surface of the pump body. More on this to come …

cb%20in1%20(Medium).jpg

Inserting the cam ring makes the pumping cavities apparent and the low pressure vs. high pressure zones are highlighted. Try to imagine the void in the shape of the front plate above that is no longer visible and how it feeds into the yellow section in the pic below.

cb%20in2%20(Medium).jpg

Following are just some other pics of the cam ring with rotor and vanes. You can see the holes at the base of the vanes that fill with pressurized fluid to keep them pushing outwards.

cb%20cam%20pack%20rear%20(Medium).jpg


cb%20cam%20pack%20front%20(Medium).jpg

Below is a photo of the front side of the rear bulkhead. A small amount of high pressure fluid is bled off the vanes up through the outside holes shown. On the back side of the bulkhead there are pathways that route it back in and down to the center of the cam ring to lube and help actuate the vanes. (See second pic.) The back plate of the pump housing is not pictured but it is shown later in some comparison pics. As high pressure fluid leaves out the back of the outer holes it also pushes against this back plate, forcing the entire cam assembly forward against the front of the pump body and creating the seal that was previously discussed.

cb%20back%20plate%20front%20(Medium).jpg

cb%20in3%20(Medium).jpg
 
#4
p%20pilot%20(Medium).jpg

Starting with the outside of the P-Pump’s cast body you see the red pressure outlet and the yellow fluid inlet. The P-Pump has an inlet on both sides that tee into a single pathway internally. You can also see the pilot fluid pathway and how it was drilled and capped during manufacture. Below are just some other angles of the same. You can see through one inlet out the other inlet on the opposite side in one of the pics.

p%20in%20(Medium).jpg

p%20out%20(Medium).jpg

Looking into the bare housing you can see how the two inlets tee into one single port inside the pump. High pressure fluid exits through the two ports closest to the camera. The P-Pump high and low pressure zones are split by two o-rings. I have colored the two zones accordingly. The P is opposite the previous two pumps discussed in that their high pressure zones are in the front of the pump whereas the P’s is in the back. No matter …

p%20case%20(Medium).jpg

p%20int%201%20(Medium).jpg

Above the vane rotor and front plate are installed. Like the CB, fluid enters the vanes via the openings left by the shape of the front plate. The high pressure fluid is pumped backwards up through ports created by the depression cast into the front plate where you see the red dots. With the cam ring installed in the next pic you can now see how this is accomplished. If you view the red dots as arrows pointing directly at you it makes more sense.

p%20int%202%20(Medium).jpg

p%20int%203%20(Medium).jpg

As high pressure fluid is pumped back toward the rear bulkhead of the pump it exits the rear of the back plate and fills the high pressure zone interior of the body. Most exits the pump at that point but some is forced back down the holes in the center of the back plate into the center of the vane rotor where it lubes and forces the vanes outwards just like in all the other pumps. Below are some other shots of the back plate and how fluid flows through it. The first one is the view from the front side of the back plate and the second is the back side.

p%20back%20plate%20front%20(Medium).jpg


p%20back%20plate%20rear%20(Medium).jpg
 
#5
The original reason I took all of these pumps apart was to measure their exact displacements. However, it turned out that there was just no good way to do this and ultimately it means little anyway if you are just comparing P, CB, and TC pumps to one another. What matters is their displacement relative to one another which becomes apparent in the following pics. What matters is the internal size and thickness of the cam ring.

Comparison of all the pumps’ cam rings:

cam%20rings%20compare.jpg

I realize the writing is somewhat small but if I posted a huge pic everyone would complain about the size of the pic. I was extremely surprised by what I found in this comparison though. The internal size of the cam ring from the aftermarket P, OEM P, and OEM CB is virtually IDENTICAL. What’s more, the thickness of the OEM P and CB are also identical. This means that, assuming the vane rotors are the same size and there is the same number of vanes in each, they should have nearly identical outputs. (It comes as no surprise that the TC is smaller than the rest.) So what about the rotors and vanes?

cams%20compare.jpg

Yup, all identical except the TC being the runt of the litter. Thus, OEM CB = OEM P in terms of output capacity. Let’s compare the back plates and rear bulkheads of all the pumps:

back%20plates%20(Medium).jpg

This comparison is important because most of the time when upping pump pressure the rear bulkhead, whether that be the back plate (as in the case of the TC) or just a tin cover (as in all the other cases), is what blows out when there is too much. Notice how the aftermarket P is convex and the OEM P is concave? There is a reason for this. The aftermarket P’s cam pack assembly is .2” thicker than the OEM P. The net result of this is that the aftermarket P has ~30% greater capacity than the OEM P! The back plate is convex to make room for the thicker cam pack. “So obviously, it’s better to buy aftermarket for increased capacity, right?” Not necessarily. The thicker cam pack in the aftermarket pump, as discussed in this thread (http://www.pirate4x4.com/forum/showthread.php?t=708701&highlight=convex+pump), was just a different internal design used by Sagninaw and until recently was readily available. While all of my stock P-Pumps had the concave back plate, all of my aftermarket pumps had the convex one with the thicker cam packs. I verified this by taking apart yet another aftermarket pump (no pics) and confirming. And while both aftermarket pumps were from different companies, the cam rings and vane rotors both had the same exact castings and machine marks. Other than these differences, the aftermarket and OEM P-Pumps that I have all appeared to be identical. And while it is possible that there are material differences that are not visible to the naked eye, to me it appears that the aftermarket pumps THAT I AM IN POSSESSION OF have nothing done internally that is different than stock other than having the larger internals that were originally offered by Saginaw. (Comparison pic below.)

p%20assy%20compare%20(Medium).jpg


There were no other differences that I could identify aftermarket vs. OEM. None of the internal passageways in the aftermarket pumps were larger or anything. Some of the aftermarket pumps did have the West Texas Mods performed on the valve bodies that are so popular, others didn’t. “So assuming we can’t get a hold of the larger internal versions of the P-Pump, we’re still better off buying aftermarket, right?” My answer is MAYBE and it is open to debate.

You see, to have 30% more OUTPUT, you have to have 30% more INPUT. Like I said, the passages leading into the pump were the same size between large internal and small internal P-Pumps. This MAY explain why the aftermarket pumps I’ve had in the past were so much more prone to cavitation, especially at higher RPMs. No matter what size supply line you have, there is still a bottle neck where the fluid enters the pump. And if you can’t supply the 30% higher input, you won’t get the 30% higher output. Most likely, all you will get is the dreaded CAVITATION.

“So why did all your pumps die prematurely?” I have a theory about this, too. Back when I ran these pumps I was using a 3/8 ID return line. I didn’t know any better. Apparently neither did the aftermarket guys though because I asked some about it on more than one occasion and they said it was OK. It’s not and they recommend at least ½ now. I was choking my system off badly and it is my theory that the pumps were cavitating and/or building excessive heat because of it. In fact, all of my pumps from the past may not be dead now that I think about it! There is one for sure that is though. That is the one that was on my rig when I wrecked it. From what I hear (I was I the hospital during the time.) it was driven back to camp with a tear or something in one of the lines and it was cavitating badly. They had to stop every few hundred feet to refill the system due to this leakage. A good explanation about cavitation can be found here: http://en.wikipedia.org/wiki/Cavitation

One of the best images I’ve seen is there and shows how cavitation can cause damage to the surfaces that it forms on:



Here is the cam ring from the pump on my last buggy that was wrecked. You can see the pitting caused by the cavitation. I have no doubt that this pump is toast:

cavitation%20(Medium).jpg


Finally, to answer the initial questions proposed in this thread:

“What are the differences between the 3 popular styles of pumps?”
Different designs offer different advantages. The OEM P and CB pumps are identical in output capability and similar in durability. However, the P has room for larger internals that the CB does not appear to have.
The TC, while smaller in capacity, has roller bearings which would seem to indicate that it is better for higher RPM. But I have yet to find an OEM application that truly does spin it much faster than either the P or CB. Whether it really can safely spin the mythical 9000 RPM that some claim is open to speculation. If it can, how long can it do it for?

“Which style is most suited to our needs?”
This really depends on your setup. For higher revving engines the TC may be better at the expense of lower output. For engines that already have bracketry for a TC who just want a little higher volume at idle, the CB may be a good choice. If you just want the most volume and damn everything else, the bigger of the P-Pumps is your hawse.

“What is causing the demise of my pumps?”
At first my theory was that it had something to do with the miniscule return line size I was using. I’m not so sure about that anymore though and am open to theories. In fact, I’m even open to the possibility that my pumps aren’t dead at all and possibly just were starving for incoming fluid.

“What are the aftermarket manufacturers doing to gain performance?”
Not much THAT I CAN TELL to the pumps that I CURRENTLY AM IN POSSESSION OF. I’m willing to bet that if they can get the larger internal version of the P-pumps we can to. I am willing to admit that I could be overlooking something. I would love to know what that is.

“Can I perform modifications on my own to improve performance similar to what the aftermarket companies do?”
Absolutely! Do the West Texas mods (http://westtexasoffroad.homestead.com/powersteering.html) and get the bigger internals for your p-pump and you’re about there as far as I can tell. :)

I hope this info has been as informative to you as it has been to me. Sorry for the long read.

J. J.
 
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