1engineer
Moderator
*warning* long technical boring post.
So [MENTION=66389]BlackWorksInc[/MENTION] (a very good and competent Toyota Tech and not a bad writer lol) asked how engineers can come up with absolute BS and get away with it. I am going to answer but no hard feelings OK? I always try to be honest with my answers and that tends to make people who are used to coddling (you know the type) very uncomfortable when they are told they are full of it. [MENTION=66389]BlackWorksInc[/MENTION] is definitely NOT full of it but some of you guys reading this are, and you know it haha.
The original thread is about rust (good luck with it) and I figured this is a topic of it's own and didn't want to take away from that. A link to the thread that is pertinent http://www.toyota-4runner.org/5th-gen-t4rs/163350-rust-starting-my-lift-gate-already-%-*-$-3.html and the pertinent TSB links are here http://www.rav4world.com/tsb/2011/T-SB-0117-11.pdf http://www.toyota-4runner.org/attac...11-shock-absorber-replacement-criteria-1-.pdf
Case 1: The Mystery of the Healing Pump
http://www.rav4world.com/tsb/2011/T-SB-0117-11.pdf
[MENTION=66389]BlackWorksInc[/MENTION] said - Notice what they consider "possible temporary leaks!" I don't care what idiotic engineer spewed his BS on this TSB and called it justification for why the pumps are "self-sealing" it makes absolutely no sense. They even state that while grooves and wear occurs on the plate once it pushes the debris out it will somehow seal itself even though now the sealing surface is now marred. Perhaps [MENTION=66316]1engineer[/MENTION] (more calling on him for his experience as an engineer than putting him down, just to be clear) can help me comprehend this, because I just don't speak this Toyota Engineer's BS. Its pretty cut and dry to me from experience and design, if a sealing surface is marred, it leaks and cannot stop leaking unless an outside force corrects the imperfection (i.e. use of FIPG, replace the sealing surface, refinish the sealing surface, ect.)
Answer :
Engineers are notorious for using the wrong words and not being able to articulate thoughts and concepts to anyone else except another engineer. The ones who can communicate and can actually dress themselves with matching shoes (probably the socks don't match though and they don't care) are immediately moved to management and taken out of the loop.
With that said here is an explanation for "self healing" water pumps:
First, this pump itself is not self healing. It is a simple low pressure impeller pump and the inherent design of this unit will never lend itself to "heal" on its own. There is a type of pump though that is designed to be self healing from contamination. It's called a vane pump and its design will let the vane tips wear any imperfection caused by contamination back smooth and reseal the mating surface.
Back to the water pump: Yes, I just said the pump is not self healing but guess what: The seals are, to a point! If you study the TSB cut away drawings of the pump you will see a spring behind the seal. That spring pushes the mating surfaces together to insure positive contact. If contamination gets between the seals's rotating surface and the fixed surface then the seal, although having a slightly damaged surface, will eventually wear that damaged portion down and reseal again. Why? Because the spring keeps pushing the seal into the mating surface. They also thoughtfully provided a nice path to flush any debris out. The key here, and what they didn't say, is this is for teeny tiny particles and imperfections. Any contamination of any size will ruin the seal but fortunately big contamination has a tough time of working it's way between the mating surfaces. In reality this is one of a very few ways you can get a pump to stay sealed for a long time with no maintenance out there. It's simple, economical and will typically last a long time and it even fixed itself to a point. The problem is weepage. Consumers do not want anything to ever weep, or leak or break. They think this crap is magic and anything is possible for a small sum of money.
The sad part of this is the engineers THOUGHT they gave you a great explanation on how this works. On page 3 of the TSB they wrote explanation 1 and thought they told you everything you needed to know. Sadly most lay people need just a bit more context to understand concepts.
Oh, and engineers are famous for saying "Just trust me" and expecting everyone to blindly say "duh, OK" just because an engineer said it. Yes, we sadly lack in most social skills including communication with everyone who is not an engineer. Sorry.
Bottom line: That seal is "self healing" to a point. The customer won't like coolant all over his block and floor during the healing process though! Geez, let me go get a drink before continuing OK? (it's like 1:00 am here)
Alright, I'm back. This is a long explanation and in order to understand the "Why" I have to give you a lot of background.
Case 2 - The Great Shock Weepage Mystery. [MENTION=90511]whiplash[/MENTION]Willy this applies to you too.
Here's their Shock Absorber Replacement Criteria TSB:
T-SB-0145-11-Shock Absorber Replacement Criteria (1).pdf
[MENTION=66389]BlackWorksInc[/MENTION] said - While I understand shocks will sweat some, the basic principle is simple with shocks; they have gas and liquid inside of them. Typically the Gas is a smaller molecule than the liquid hydraulic fluid (based on my knowledge that most every shock is Nitrogen charged) so if the shock is leaking enough that fluid is getting out; do you think that gas charge isn't already starting to leak out? So if its getting to close to 1/2 down the strut I would consider that shock's performance to be severely compromised, wouldn't you? I mean its not like shocks help reduce stopping distance or provide stability in emergency maneuvers right?
Answer:
I really don't know where to begin here so I will start with this link: Shock absorber - Wikipedia, the free encyclopedia
This link explains the basic operation of a shock absorber and more importantly, it shows pictures! The most important take away is this: The fluid and gas NEVER touch. Let me repeat a little differently: In a closed hydraulic system that uses a nitrogen precharge (KDSS shocks, nitrogen precharged automotive shocks and even big hydraulic systems) the fluid and gas are never mixed. Got it? In some hydraulic systems, there is a bladder filled with pressurized nitrogen inside a pressure vessel. Oil is introduced into this vessel under pressure and capped. When needed for use, this oil is pressurized and ready to go. Another type uses a piston with one side being pressurized nitrogen(why nitrogen? Because it's inert and stable-er to temperature changes and cheap) and pressurized hydraulic fluid on the other side of the piston. There is a seal that keeps them separate.
If you go back to that Wiki link I just posted look down the right side of the page to the "Mono Tube" shock cut away. It's very simple and has a good illustration showing what it looks like inside. Remember all the physics are the same no matter what design the engineers use.
Gas under pressure - fluid under pressure - separated by a seal.
So now let me give you an example. I will just pick some pressures out of the air to use here OK?
Given:
Simple monotube (like the one in the Wiki article) Shock
Nitrogen Gas is precharged to 100 PSI
Maximum shock hydraulic fluid pressure is 200 psi
What will happen is under normal load the shock is static and not moving cruising on a perfectly smooth road. The shock is extended and there is 100 psi pressure in both the nitrogen and hydraulic fluid chambers. Now, you hit a bump and instantly the shock gets compressed. Because you are pushing a lot of fluid quickly through an orifice in the shock (please don't make me go through the orifice and pressure drop equations, you would really hate me then) the pressure rises to say 300 psi in the fluid side. Since my nitrogen only had 100 psi to start, the shock compresses until A)The nitrogen side gets to 300 psi or B)The bypass opens and bleeds pressure to the back side.
Got it? Good. Now here is the actual reason that a little "weepage" is not a bad thing on a shock and why it won't hurt performance.
I explained above about the pressures of the nitrogen and the hydraulic fluid. What I didn't cover is the VOLUME of the nitrogen or the hydraulic fluid. Both volumes are critical to the proper operation of a shock. Since Nitrogen is contained in a separate part of the shock and does not change much due to temperature then the nitrogen volume is pretty safe, unless you just really abuse the shocks.
The hydraulic fluid, on the other hand, is not so lucky. Temperature will change the viscosity, a lot. Ever went out and started driving the 4Runner or a really cold morning and for the first minute or two it felt like your suspension is completely rigid? Yep, that's why. Your fluid in the shock is COLD and even though the fluid is top of the line temperature will change the viscosity. After just a minute though the suspension feels normal. That's because the shocks are working a lot, going up and down and that causes heat. That's the reason for remote mounted reservoirs on some shocks. Anyway, back to the weepage and volumes:
A shock has a fixed amount of fluid. For the sake of argument let's say 5 cubic inches. So that's 5 cubic inches in there under a pressure, and at rest it would be the same as the nitrogen precharge. Let's say, due to heat changing the viscosity of the fluid and something I call the "bonding layer" in fluid flow theory (link http://www.freestudy.co.uk/fluid mechanics/t1203.pdf for a good explanation) you are just going to leak a little fluid over a period of time. You really need to have a thorough understanding of Fluid Mechanics for a good explanation but suffice to say no matter how good the seal you will get a thin film on the rod. Over time this will be seen as "weepage" on the shock boot.
Back to volumes: In reality you have only lost a small amount of fluid from that 5 cubic inches you started with. Say maybe down to 4.999 cubic inches. Such a small amount will not change the operation or the performance of the shock but you will see the weepage. Now, if you lose a lot, say 1 cubic inch, then that will change the operation of the shock a lot! If you have ever spilled a drop of water on a hard floor you know how much you can spread that one drop!
The reason they show you the pictures in the TSB of "how much can weep befor being abnormal" is simply this: They have performed experiments and are just giving you a quick visual on how much is too much weepage. I probably wouldn't have used the word "evaporation" even though it technically could be called that. Then again there really isn't a good thing to call it besides "bonding layer displacement" and that's just misleading as hell too.
Anyway, hope this helps. Cut the engineers a break. They are usually only stupid when it comes to proper communication lol.
So [MENTION=66389]BlackWorksInc[/MENTION] (a very good and competent Toyota Tech and not a bad writer lol) asked how engineers can come up with absolute BS and get away with it. I am going to answer but no hard feelings OK? I always try to be honest with my answers and that tends to make people who are used to coddling (you know the type) very uncomfortable when they are told they are full of it. [MENTION=66389]BlackWorksInc[/MENTION] is definitely NOT full of it but some of you guys reading this are, and you know it haha.
The original thread is about rust (good luck with it) and I figured this is a topic of it's own and didn't want to take away from that. A link to the thread that is pertinent http://www.toyota-4runner.org/5th-gen-t4rs/163350-rust-starting-my-lift-gate-already-%-*-$-3.html and the pertinent TSB links are here http://www.rav4world.com/tsb/2011/T-SB-0117-11.pdf http://www.toyota-4runner.org/attac...11-shock-absorber-replacement-criteria-1-.pdf
Case 1: The Mystery of the Healing Pump
http://www.rav4world.com/tsb/2011/T-SB-0117-11.pdf
[MENTION=66389]BlackWorksInc[/MENTION] said - Notice what they consider "possible temporary leaks!" I don't care what idiotic engineer spewed his BS on this TSB and called it justification for why the pumps are "self-sealing" it makes absolutely no sense. They even state that while grooves and wear occurs on the plate once it pushes the debris out it will somehow seal itself even though now the sealing surface is now marred. Perhaps [MENTION=66316]1engineer[/MENTION] (more calling on him for his experience as an engineer than putting him down, just to be clear) can help me comprehend this, because I just don't speak this Toyota Engineer's BS. Its pretty cut and dry to me from experience and design, if a sealing surface is marred, it leaks and cannot stop leaking unless an outside force corrects the imperfection (i.e. use of FIPG, replace the sealing surface, refinish the sealing surface, ect.)
Answer :
Engineers are notorious for using the wrong words and not being able to articulate thoughts and concepts to anyone else except another engineer. The ones who can communicate and can actually dress themselves with matching shoes (probably the socks don't match though and they don't care) are immediately moved to management and taken out of the loop.
With that said here is an explanation for "self healing" water pumps:
First, this pump itself is not self healing. It is a simple low pressure impeller pump and the inherent design of this unit will never lend itself to "heal" on its own. There is a type of pump though that is designed to be self healing from contamination. It's called a vane pump and its design will let the vane tips wear any imperfection caused by contamination back smooth and reseal the mating surface.
Back to the water pump: Yes, I just said the pump is not self healing but guess what: The seals are, to a point! If you study the TSB cut away drawings of the pump you will see a spring behind the seal. That spring pushes the mating surfaces together to insure positive contact. If contamination gets between the seals's rotating surface and the fixed surface then the seal, although having a slightly damaged surface, will eventually wear that damaged portion down and reseal again. Why? Because the spring keeps pushing the seal into the mating surface. They also thoughtfully provided a nice path to flush any debris out. The key here, and what they didn't say, is this is for teeny tiny particles and imperfections. Any contamination of any size will ruin the seal but fortunately big contamination has a tough time of working it's way between the mating surfaces. In reality this is one of a very few ways you can get a pump to stay sealed for a long time with no maintenance out there. It's simple, economical and will typically last a long time and it even fixed itself to a point. The problem is weepage. Consumers do not want anything to ever weep, or leak or break. They think this crap is magic and anything is possible for a small sum of money.
The sad part of this is the engineers THOUGHT they gave you a great explanation on how this works. On page 3 of the TSB they wrote explanation 1 and thought they told you everything you needed to know. Sadly most lay people need just a bit more context to understand concepts.
Oh, and engineers are famous for saying "Just trust me" and expecting everyone to blindly say "duh, OK" just because an engineer said it. Yes, we sadly lack in most social skills including communication with everyone who is not an engineer. Sorry.
Bottom line: That seal is "self healing" to a point. The customer won't like coolant all over his block and floor during the healing process though! Geez, let me go get a drink before continuing OK? (it's like 1:00 am here)
Alright, I'm back. This is a long explanation and in order to understand the "Why" I have to give you a lot of background.
Case 2 - The Great Shock Weepage Mystery. [MENTION=90511]whiplash[/MENTION]Willy this applies to you too.
Here's their Shock Absorber Replacement Criteria TSB:
T-SB-0145-11-Shock Absorber Replacement Criteria (1).pdf
[MENTION=66389]BlackWorksInc[/MENTION] said - While I understand shocks will sweat some, the basic principle is simple with shocks; they have gas and liquid inside of them. Typically the Gas is a smaller molecule than the liquid hydraulic fluid (based on my knowledge that most every shock is Nitrogen charged) so if the shock is leaking enough that fluid is getting out; do you think that gas charge isn't already starting to leak out? So if its getting to close to 1/2 down the strut I would consider that shock's performance to be severely compromised, wouldn't you? I mean its not like shocks help reduce stopping distance or provide stability in emergency maneuvers right?
Answer:
I really don't know where to begin here so I will start with this link: Shock absorber - Wikipedia, the free encyclopedia
This link explains the basic operation of a shock absorber and more importantly, it shows pictures! The most important take away is this: The fluid and gas NEVER touch. Let me repeat a little differently: In a closed hydraulic system that uses a nitrogen precharge (KDSS shocks, nitrogen precharged automotive shocks and even big hydraulic systems) the fluid and gas are never mixed. Got it? In some hydraulic systems, there is a bladder filled with pressurized nitrogen inside a pressure vessel. Oil is introduced into this vessel under pressure and capped. When needed for use, this oil is pressurized and ready to go. Another type uses a piston with one side being pressurized nitrogen(why nitrogen? Because it's inert and stable-er to temperature changes and cheap) and pressurized hydraulic fluid on the other side of the piston. There is a seal that keeps them separate.
If you go back to that Wiki link I just posted look down the right side of the page to the "Mono Tube" shock cut away. It's very simple and has a good illustration showing what it looks like inside. Remember all the physics are the same no matter what design the engineers use.
Gas under pressure - fluid under pressure - separated by a seal.
So now let me give you an example. I will just pick some pressures out of the air to use here OK?
Given:
Simple monotube (like the one in the Wiki article) Shock
Nitrogen Gas is precharged to 100 PSI
Maximum shock hydraulic fluid pressure is 200 psi
What will happen is under normal load the shock is static and not moving cruising on a perfectly smooth road. The shock is extended and there is 100 psi pressure in both the nitrogen and hydraulic fluid chambers. Now, you hit a bump and instantly the shock gets compressed. Because you are pushing a lot of fluid quickly through an orifice in the shock (please don't make me go through the orifice and pressure drop equations, you would really hate me then) the pressure rises to say 300 psi in the fluid side. Since my nitrogen only had 100 psi to start, the shock compresses until A)The nitrogen side gets to 300 psi or B)The bypass opens and bleeds pressure to the back side.
Got it? Good. Now here is the actual reason that a little "weepage" is not a bad thing on a shock and why it won't hurt performance.
I explained above about the pressures of the nitrogen and the hydraulic fluid. What I didn't cover is the VOLUME of the nitrogen or the hydraulic fluid. Both volumes are critical to the proper operation of a shock. Since Nitrogen is contained in a separate part of the shock and does not change much due to temperature then the nitrogen volume is pretty safe, unless you just really abuse the shocks.
The hydraulic fluid, on the other hand, is not so lucky. Temperature will change the viscosity, a lot. Ever went out and started driving the 4Runner or a really cold morning and for the first minute or two it felt like your suspension is completely rigid? Yep, that's why. Your fluid in the shock is COLD and even though the fluid is top of the line temperature will change the viscosity. After just a minute though the suspension feels normal. That's because the shocks are working a lot, going up and down and that causes heat. That's the reason for remote mounted reservoirs on some shocks. Anyway, back to the weepage and volumes:
A shock has a fixed amount of fluid. For the sake of argument let's say 5 cubic inches. So that's 5 cubic inches in there under a pressure, and at rest it would be the same as the nitrogen precharge. Let's say, due to heat changing the viscosity of the fluid and something I call the "bonding layer" in fluid flow theory (link http://www.freestudy.co.uk/fluid mechanics/t1203.pdf for a good explanation) you are just going to leak a little fluid over a period of time. You really need to have a thorough understanding of Fluid Mechanics for a good explanation but suffice to say no matter how good the seal you will get a thin film on the rod. Over time this will be seen as "weepage" on the shock boot.
Back to volumes: In reality you have only lost a small amount of fluid from that 5 cubic inches you started with. Say maybe down to 4.999 cubic inches. Such a small amount will not change the operation or the performance of the shock but you will see the weepage. Now, if you lose a lot, say 1 cubic inch, then that will change the operation of the shock a lot! If you have ever spilled a drop of water on a hard floor you know how much you can spread that one drop!
The reason they show you the pictures in the TSB of "how much can weep befor being abnormal" is simply this: They have performed experiments and are just giving you a quick visual on how much is too much weepage. I probably wouldn't have used the word "evaporation" even though it technically could be called that. Then again there really isn't a good thing to call it besides "bonding layer displacement" and that's just misleading as hell too.
Anyway, hope this helps. Cut the engineers a break. They are usually only stupid when it comes to proper communication lol.
eep:
![sheldon-whiteboard[1].jpg](https://www.toyota-4runner.org/data/attachments/86/86183-4ebac4b148dfd21b282bb32faf596b05.jpg?hash=HnnCBBEqxy "sheldon-whiteboard[1].jpg")
![sheldon-whiteboard[1].jpg](/data/attachments/86/86183-4ebac4b148dfd21b282bb32faf596b05.jpg?hash=HnnCBBEqxy)
