Explanation of MBC leak on boost leak tests

[burntheblobs]

Can someone explain to me how this ISN'T a boost leak? I have it set to 12psi, and it will leak heavily when there is about 1psi in the system. Everyone always says it's totally ok, but why? A leak is a leak in my mind...

 

[donmagicjuan]

What were all trying to say here it this this wont happen, The spring its self hold the pressure back untill 18PSI or in this story 16. I do see what your saying though, and I, as well could be worng. Lets join and E debate team

I'm well aware that everyone is disputing this part of my argument. That's why I came up with a timeline that fully explains why it's conceivable that it does in fact happen this way. I would welcome an alternative explanation that disproves this pivotal assumption.

 

[EclipseTrbo420A]

I'm well aware that everyone is disputing this part of my argument. That's why I came up with a timeline that fully explains why it's conceivable that it does in fact happen this way. I would welcome an alternative explanation that disproves this pivotal assumption.

How about this one BOOST SPIKE !

The closer the MBC to the actuator the less boost spike you have. Why, you ask? Because there is NO pressure after the MBC....nothing goes on there untill the ball is moved at 18PSI. Then when open, it rushes to the acutator blowing it open.

So if my MBC is right at the Intake manifold the pressure will build there, and if it is right on the actuator the pressure will build there.

The MBC on the manifold reaches 18 PSI and then opens...the pressure has to flow all the way down to the actuator before it can open it and regulate boost..since it takes so long the turbo will spool to say 22 before the pressure ever reaches the actuator and settles it back at 18PSI.

If the MBC were right on the actuator it would take a split second to get to the actuatot and open right away resulting in NO boostcreep.

This if fact...I know from experience. Thoughts ?

 

[donmagicjuan]

I would argue that the responsiveness of the MBC is more a function of the total line length between the boost source and the WGA, not just the line from the MBC to the WGA. Nonetheless, I agree on the overall effect. However, I don't see how this disproves my point. In either case, a longer line will result in more time for pressure to accumulate at the WGA, thereby lowering the repsonse of the controller. Whether the pressure starts at zero in the line or whether it rises linearly once boost exceeds the initial D/P setting, a rapidly rising boost pressure coupled with excessively long boost controller lines will yield the same result.

The problem I have with your theory lies in the events that immediately follow the setpoint of the MBC being reached. Let's assume the MBC valve opens at exactly 16 psig. With zero pressure in the WGA line, this corresponds to a D/P of 16 psid. But what happens as pressure starts to accumulate in the WGA line? The D/P across the valve will start to drop, allowing the spring to eventually overcome it and shut the valve. There's no possible way that the pressure could have built up in the WGA line long enough to open the wastegate, cause boost to lower, shut the MBC valve, and allow pressure to be bled to zero again before the cycle repeats itself. This is a very dynamic process. Everything is happening extremely fast, and the valve is cycling at its setpoint when controlling boost (agreed?). Your argument assumes that the WGA line pressure is cycling between 0 and 16 psig MANY times per second. Doesn't that seem a little counterintuitive?

 

[EclipseTrbo420A]

I would argue that the responsiveness of the MBC is more a function of the total line length between the boost source and the WGA, not just the line from the MBC to the WGA. Nonetheless, I agree on the overall effect. However, I don't see how this disproves my point. In either case, a longer line will result in more time for pressure to accumulate at the WGA, thereby lowering the repsonse of the controller. Whether the pressure starts at zero in the line or whether it rises linearly once boost exceeds the initial D/P setting, a rapidly rising boost pressure coupled with excessively long boost controller lines will yield the same result.

The problem I have with your theory lies in the events that immediately follow the setpoint of the MBC being reached. Let's assume the MBC valve opens at exactly 16 psig. With zero pressure in the WGA line, this corresponds to a D/P of 16 psid. But what happens as pressure starts to accumulate in the WGA line? The D/P across the valve will start to drop, allowing the spring to eventually overcome it and shut the valve. There's no possible way that the pressure could have built up in the WGA line long enough to open the wastegate, cause boost to lower, shut the MBC valve, and allow pressure to be bled to zero again before the cycle repeats itself. This is a very dynamic process. Everything is happening extremely fast, and the valve is cycling at its setpoint when controlling boost (agreed?). Your argument assumes that the WGA line pressure is cycling between 0 and 16 psig MANY times per second. Doesn't that seem a little counterintuitive?

I think your not understanding what Im writing. The turbo is pushing pressure...continusly. Enough pressure to hold everything at 16 PSI even with the bleeder hole LEAKING, not LOWERING pressure. Once the ball is moved its staying moved....no alteration. Thats whay I believe. Thats why a turbo can make the needed amount of pressure even with a boost leak...as small boost leak...like a small bleeder hole. If it were a big boost leak, sometimes you cant build boost.....if the bleeder hole were significanly larger than the path to the WGA then thats where the boost pressure would go all 16LBS of it away from the WGA . See?

By the way Im having a good time here and want no hard feelings to arise. You a cool guy with a lot of knowledge and a great tuner. Friends? After this is done, I think were should discuss another topic where he have different views and see what happends there as well. I like racking my brain.

 

[donmagicjuan]

By the way Im having a good time here and want no hard feelings to arise.

None whatsoever. I don't take offense to someone honestly disagreeing with a point.

Once the ball is moved its staying moved....no alteration. Thats whay I believe.

This is a simple case of Newtonian physics. With the pressure equalized on either side of the MBC valve, the system exerts zero net force on the ball. If this were where it ended, I would have no gripes with your theory. The problem I have is the effect of the spring. With no net force exerted on the ball by the system, the only thing left acting on the ball is the spring. Therefore, the net force on the ball is nonzero, and the ball will accelerate in the direction of the force of the spring. This will continue until either 1) the valve shuts or 2) the D/P across the valve overcomes the force of the spring once again. What will not happen is the valve hanging open all fat, dumb, and happy with 16 psig on either side of it.

 

[kenamond]

I still have to read about 8 posts to catch up, but Don's right. We were focusing on what it would take to open the MBC for the first time *and* have it open the WGA. That's not at all important, because what we care about is the steady state boost control which is a state where the WGA is constantly open. In this state, the WGA pressure cannot be equal to the upwind pressure, or the MBC wouldn't be open. The steady state configuration has at least 8psi in the WGA line and some higher pressure upwind in order to keep the MBC valve open. The MBC has to be adjusted just right so that at the desired D/P the air flowing around the ball has to exactly equal the amount of air leaking out of the vent hole. This D/P is what you set on the MBC. If you raise the spring compression, the D/P across the ball has to be higher to get it to flow the same amount of air that is venting from the vent hole. Also, the rate at which air bleeds out of the downwind side will depend on the pressure forcing it through that little hole. We care about one pressure in there: 8psi. So let's say that it flows 1cc/s out the hole when the downwind pressure is at 8psi. This means that if we set the MBC to a D/P of 1psi, that valve will open up just enough to let 1cc/s past the ball when the upwind pressure is 1psi higher than the downwind pressure. If the D/P is 0.5psi, more air leaks from the vent than is going past the ball, so the pressure in the WGA is dropping and it is closing the flapper. Now we tighten up the spring so that it lets 1cc/s past the ball when the D/P is 5psi. That means that you need to get the upwind pressure up to 13psi. If it goes to 14psi, the D/P will be larger and move the ball more which will let the flow exceed 1cc/s. This overwhelms the vent hole, and the WGA pressure goes up opening the WGA more which lowers (controls) the boost.

Here's were I go back and read the previous posts and find out I just repeated 5 people.

 

[JayRolla]

Thats for sure im learning a lot just reading your guys's debate.

 

[kenamond]

One clarification (maybe correction) is that I don't think the MBC opens and shuts at some high frequency. I believe everything evolves smoothly in equilibrium. Let's say you know the flow rate through the vent hole is as follows (pressure vs. flow rate):

Pressure(psi) Flowrate(cc/s)
0 0.00
1 0.10
3 0.30
5 0.50
8 0.60
9 0.65
10 0.70

Notice that it's flowing less and less as the pressure goes up (that would be the case, since pressure drop goes up nonlinearly with flow for a fixed orifice size).

And let's say that you set the MBC through trial and error to give you 16psi boost. Then you disconnect the MBC and drill out the vent to some ungodly large size so that it flows perfectly and do an experiment to find out the flowrate past the ball as a function of D/P and get the following:

D/P(psi) Flowrate(cc/s)
0 0.0
1 0.0
4 0.0
5 0.1
6 0.3
7 0.5
8 0.6
9 0.7

The MBC doesn't open at all until maybe 4psi D/P and then starts to open. The flow past the ball then raises (linearly) 0.2cc/s for each additional psi of D/P. Since this is a ball-spring device rather than an orifice, the flow will continue to keep up with the D/P until you get to REALLY high flowrates (note that this is hypothetical - the actual flow characteristics will probably not be linear, but they will outflow the vent hole at high pressures for sure).

When the MBC is open at any point, there will be a certain inflow of air F1 past the ball and an outflow of air F2 out the vent hole. If F1>F2 then the downwind pressure will rise (more air entering the WGA line than exitting means the pressure in that line has to go up), but that will cause F2 to raise as well (based on the first list of flow numbers). So if you increase F1, F2 will keep up up to a point.

Looking at the fictitious data, if you immediately apply 6psi boost, it will start leaking at 0.3cc/s into the WGA line which starts out at 0psi flowing 0cc/s, so the outflow is less than the inflow and the pressure in the WGA line starts to rise. As it rises, the D/P falls, because we're still at 6psi boost, but the downwind pressure is rising. Eventually, it settles on an equilibrium flow rate of 1cc/s, because that gives 1psi in the WGA and 5psi D/P across the ball, and 1psi+5psi = 6psi. That means that at a boost of 6psi, the WGA is seeing 1psi.

Now, as you raise the boost to 9psi, that works out to an equilibrium flow of 0.3cc/s both past the ball and out the vent hole, where the D/P is 6psi and the WGA pressure is 3psi (3+6=9, and the flows are equal). The WGA is only seeing 3psi, so the turbine is still fed all the exhaust.

Eventually, you get to 16psi where the equilibrium flows are 0.6cc/s and get a D/P of 8psi and a WGA of 8psi which begins to open the WGA. This begins diverting exhaust around the turbine. If you go to 19psi, the flows would both be 0.7cc/s, but that'd be 10psi in the WGA which has the flapper now thrown wide open - so you wouldn't actually get to 19psi boost, because the WGA would be keeping it from raising further. Based on my hypothetical numbers, you'd settle on a boost greather than 16psi, and how much would depend on the effect of the WGA+flapper on the turbine and subsequently on the compressor and boost level.

You could carry the analogy to the turbine, wastegate, and compressor and construct hypothetical numbers stating that WGA pressure X will limit boost to Y (fixed RPM, timing, a/f etc.). This would tell you where the boost would settle given my hypothetical numbers above - you'd have to find the X and Y such the flow rate at X out the vent hole equaled the flow rate past the ball at D/P of Y-X. Getting complicated, but I suspect that's more like what happens than the rapid open/shut of the MBC.

That was fun! Thanks Don for your patience and persistence!

 

[donmagicjuan]

Hey, thanks for the much needed support! I was beginning to feel like I was drowning here.
My description of the cycling of the MBC valve was more an exaggeration to get my point across, but that's some good stuff there with an appreciated different approach.

 

[kenamond]

Hey, thanks for the much needed support! I was beginning to feel like I was drowning here.
My description of the cycling of the MBC valve was more an exaggeration to get my point across, but that's some good stuff there with an appreciated different approach.

It's so easy to get it wrong, because it seems like such a simple situation, but it turns out it's not so simple; a lot is going on in those things. I think many of us start out ignoring the importance of the bleeder thinking it's just a mechanism for letting the WGA close when boost drops, but it as well as the flow rates past the ball are just as significant as the ball+spring.

 

[EclipseTrbo420A]

Ill take that, I am wrong, if you are right. If the pressure reached 18PSi on both sides of the ball....there might as well be no pressure, and the spring will be on the "pushing the ball closed team"....and win. I still thing we need to call myth busters and have them build alittle chamber simulation thing, but for now I stand corrected.

On a side note..we tied our game tonight as it ended in the 13th inning due to darkenss. I was thinking about this argument at dinner just before this. Anything else we should discuss?

 

[donmagicjuan]

Ill take that, I am wrong, if you are right. If the pressure reached 18PSi on both sides of the ball....there might as well be no pressure, and the spring will be on the "pushing the ball closed team"....and win. I still thing we need to call myth busters and have them build alittle chamber simulation thing, but for now I stand corrected.

On a side note..we tied our game tonight as it ended in the 13th inning due to darkenss. I was thinking about this argument at dinner just before this. Anything else we should discuss?

I respect your ability to concede the argument with dignity. For me, the discussion is still open should you ever stumble on some evidence that you feel will overturn what I've assumed to be accurate here. While I disagreed with the principle behind it, I found your drawings particularly useful in your discussion (and somewhat entertaining). Very impressive.

 

[toojung2die]

How about this one BOOST SPIKE !
The closer the MBC to the actuator the less boost spike you have. Why, you ask? Because there is NO pressure after the MBC....nothing goes on there untill the ball is moved at 18PSI. Then when open, it rushes to the acutator blowing it open...
<snip>
This if fact...I know from experience. Thoughts ?

I'm standing with EclipseTrbo420A in this discussion.
When I started looking for a MBC I talked to my old friend who has worked for Swagelok his whole life selling stuff like precision check valves to nuclear power plants and other industries. He gave me some technical data sheets for a variety of check valves he thought I could possibly use as a MBC. One interesting fact that stuck with me is ball and spring check valves have a design defect. They have a higher pop-off pressure than more sophisticated disk and spring check valves. Pop-off means that if a ball and spring check valve is adjusted to release at 15psi it will hold pressure beyond that and not pop-off until the pressure hits maybe 16 or 17 psi and then it unseats the ball. After that happens it modulates the pressure at the 15psi set point. Swagelok engineers have made dozens of designs of sophisticated check valves all made with the intent of reducing this pop-off pressure.

Why am I saying all this? Because it means that a MBC check valve that's set to open the wastegate at 15 psi will not open until there is at least 15psi pushing against the ball. It has nothing to do with the actuator or the bleed hole or anything after the ball. Nothing happens at 8psi or anything less than 15psi. The ball remains seated and it doesn't matter what the actuator design is. The purpose of a MBC is to hold back all pressure until the desired boost set point is reached and then open to pass this pressure to the wastegate to open it.

The fact is in real life the MBC ball will not release until slightly more pressure than 15 psi is applied because of the pop-off pressure required to get the ball unseated. As a side note, the pop-off pressure is why we see higher boost spikes with less expensive MBC's.

 

[EclipseTrbo420A]

I respect your ability to concede the argument with dignity. For me, the discussion is still open should you ever stumble on some evidence that you feel will overturn what I've assumed to be accurate here. While I disagreed with the principle behind it, I found your drawings particularly useful in your discussion (and somewhat entertaining). Very impressive.

Same to you, it was fun atleast. All I know is, my 18G, hybrid clutch and Injectors will all be on my car soon and I wont have to deal with 16 or 18 psi Im going big haha

I found out theres on AWD dyno in pittsburgh so Ill have to hit that up after I get some time with the 18G and DSMLink. Well see, and If I think of anything else Ill be sure to post about it.

 

[EclipseTrbo420A]

after reading toojung2dies's post..Im beginning to rething my resignation. I have to think for a minute. Gimme a sec

 

[EclipseTrbo420A]

Im arguing my self here in my head as we speak, it all sounds right. What it we look at the 2 different types of pressure. There is a still pressure where the line is pressureized to 18PSI and then capped off and the source cut off. The ball will have moved to allow pressure to everthing, but then set back when the pressure evens out on both sides.

Now theres the MOVING pressure that is pushing on the ball, not around it. Thats a constant when the turbo is kicking. That Moving pressure is holding the ball back and unseated untill it dies down and the spring can re-seat the ball... The moving pressure comming from the manifold only hits 30% surface area of the ball, not the entire ball. Which means the pressure never pushes the ball closed. Only the spring does.

I could put a basket ball in a room and pressurize the room and the ball would not move. If I put that same ball in a passage way like the MBC ball is, and hit it with 18LBS it will move..
Im right, right ? haha

By passage way I mean where the pressure will build on the ball and not around it. again with the room....Pressurize the room and the ball will not move...pressurizethe room from where the ball is seated and it will blow the ball out of the way untill the pressure source stops. NOW when it does stop and the ball falls back to the hole the pressure will hold in the room because the ball is blocking it....unless the open a window ( bleeder valve ) and let the pressure out that way. Woot. I know your going to say what if you leave the window cracked.....the pressure source ( Turbo ) makes to much for that to be a factor. That why we can run with minor boostleaks, but the big ones we cant.

 

[kenamond]

I'm standing with EclipseTrbo420A in this discussion.
When I started looking for a MBC I talked to my old friend who has worked for Swagelok his whole life selling stuff like precision check valves to nuclear power plants and other industries. He gave me some technical data sheets for a variety of check valves he thought I could possibly use as a MBC. One interesting fact that stuck with me is ball and spring check valves have a design defect. They have a higher pop-off pressure than more sophisticated disk and spring check valves. Pop-off means that if a ball and spring check valve is adjusted to release at 15psi it will hold pressure beyond that and not pop-off until the pressure hits maybe 16 or 17 psi and then it unseats the ball. After that happens it modulates the pressure at the 15psi set point. Swagelok engineers have made dozens of designs of sophisticated check valves all made with the intent of reducing this pop-off pressure.

Why am I saying all this? Because it means that a MBC check valve that's set to open the wastegate at 15 psi will not open until there is at least 15psi pushing against the ball. It has nothing to do with the actuator or the bleed hole or anything after the ball. Nothing happens at 8psi or anything less than 15psi. The ball remains seated and it doesn't matter what the actuator design is. The purpose of a MBC is to hold back all pressure until the desired boost set point is reached and then open to pass this pressure to the wastegate to open it.

The fact is in real life the MBC ball will not release until slightly more pressure than 15 psi is applied because of the pop-off pressure required to get the ball unseated. As a side note, the pop-off pressure is why we see higher boost spikes with less expensive MBC's.

I think you should carefully read what Don and I (after some thinking) posted. Convince yourself you're right during steady state full boost where the flapper is constantly open some amount. What is going on inside that MBC in that situation? If you agree that the flapper is open and that the boost is at 15psi, then that means the WGA pressure is 8psi (remember, the flapper is open, which can only happen if the WGA is at or above 8psi) and the boost is still 15psi...so the MBC has a pressure difference across it of...what?

We contend that if you want 15psi boost with an 8psi WGA, you must set the MBC to 7psi. I don't doubt what you say about ball-spring valve pop-off issues (that's good to know). But in our situation where the MBC opens at ~7psi, that popoff might happen at 8 or 9psi, and this will happen when the turbo first spools through those boost levels. The MBC will stay popped off from then on out until you let off the gas. So it shouldn't be an issue.

 

[EclipseTrbo420A]

I think you should carefully read what Don and I (after some thinking) posted. Convince yourself you're right during steady state full boost where the flapper is constantly open some amount. What is going on inside that MBC in that situation? If you agree that the flapper is open and that the boost is at 15psi, then that means the WGA pressure is 8psi (remember, the flapper is open, which can only happen if the WGA is at or above 8psi) and the boost is still 15psi...so the MBC has a pressure difference across it of...what?

We contend that if you want 15psi boost with an 8psi WGA, you must set the MBC to 7psi. I don't doubt what you say about ball-spring valve pop-off issues (that's good to know). But in our situation where the MBC opens at ~7psi, that popoff might happen at 8 or 9psi, and this will happen when the turbo first spools through those boost levels. The MBC will stay popped off from then on out until you let off the gas. So it shouldn't be an issue.

How do you get that a chamber that is being pumped with 18LBS of air constantly can only be pressureized to a lower amount. Are you saying the WGA's 7 psi is pushing on the Turbos 18PSI and making the chamber there 11 psi? Thats not true. The WGA gets overrun and the chamber reaches 18PSI because thats what the MBC allows the turbo to do.

The WGA surface gets blown back, and all that is, is now a bigger chamber behind the ball to be filled to 18PSI. The turbo flows to much for the bleeder to have an ill effect on pressure. Thats why its kept as small as possible.

 

[kenamond]

Im arguing my self here in my head as we speak, it all sounds right. What it we look at the 2 different types of pressure. There is a still pressure where the line is pressureized to 18PSI and then capped off and the source cut off. The ball will have moved to allow pressure to everthing, but then set back when the pressure evens out on both sides.

Now theres the MOVING pressure that is pushing on the ball, not around it. Thats a constant when the turbo is kicking. That Moving pressure is holding the ball back and unseated untill it dies down and the spring can re-seat the ball... The moving pressure comming from the manifold only hits 30% surface area of the ball, not the entire ball. Which means the pressure never pushes the ball closed. Only the spring does.

I could put a basket ball in a room and pressurize the room and the ball would not move. If I put that same ball in a passage way like the MBC ball is, and hit it with 18LBS it will move..
Im right, right ? haha

By passage way I mean where the pressure will build on the ball and not around it. again with the room....Pressurize the room and the ball will not move...pressurizethe room from where the ball is seated and it will blow the ball out of the way untill the pressure source stops. NOW when it does stop and the ball falls back to the hole the pressure will hold in the room because the ball is blocking it....unless the open a window ( bleeder valve ) and let the pressure out that way. Woot. I know your going to say what if you leave the window cracked.....the pressure source ( Turbo ) makes to much for that to be a factor. That why we can run with minor boostleaks, but the big ones we cant.

Just keep in mind that the air pressure in the room controls the pressure (boost) level of the air blasting the basketball.

If you're holding the bball down, it'll seal until the pressure gets high enough that it starts leaking air (let's say you're sitting on it). If the leak is small, the air coming in around the bball can easily leak out the open window without raising the pressure of the room much...but in an engine, that means the turbo is going to boost more (flapper is closed). So the pressure under the bball is raising. It's leaking more now. The air coming into the room is now enough that the pressure in the room is a bit higher now, but the amount of air entering around the bball is still the same as the amount out the window. And the turbo is still going up in boost. Now, the air is gushing around the bball. The air going out the window at the low room pressure is less than the bball air, so the pressure in the room goes up until it is high enough to force the incoming air out that window. Eventually, the pressure in the room is high enough that it starts opening the WGA. The turbo stops increasing boost and stabilizes at 18...no!...26psi and this house is MOVIN'. We're at full boost in 4th gear for a good 5 seconds, and boy is it windy in that room!

 

[kenamond]

How do you get that a chamber that is being pumped with 18LBS of air constantly can only be pressureized to a lower amount. Are you saying the WGA's 7 psi is pushing on the Turbos 18PSI and making the chamber there 11 psi? Thats not true. The WGA gets overrun and the chamber reaches 18PSI because thats what the MBC allows the turbo to do.

The WGA surface gets blown back, and all that is, is now a bigger chamber behind the ball to be filled to 18PSI. The turbo flows to much for the bleeder to have an ill effect on pressure. Thats why its kept as small as possible.

Nonono. The ball-spring device will leak a certain amount if you apply a specific pressure differential. If you increase that differential, it'll leak more. With any partially open valve, there is a pressure drop across it. Like the butterfly in the throttle body has vaccuum on one side and 0psi on the other when it is closed, but as you open it more and more, the pressure in the IM starts to raise (the differential is going down). The same is going on in the MBC; you have boost on one side and some lower pressure on the WGA side.

When you are at 15psi boost, the WGA pressure is at 8psi and that gives a pressure drop (we're calling that a differential pressure or D/P) of 7psi across the ball-spring. We've tightened the spring just right so that it is in harmony in this situation. The spring holds the ball just hard enough that the air leaking past it into the WGA has to raise to 8psi to be able to force that exact same amount of leaking air out the vent hole.

Read my response to the basketball/room/window example.

 

[EclipseTrbo420A]

Just keep in mind that the air pressure in the room controls the pressure (boost) level of the air blasting the basketball.

If you're holding the bball down, it'll seal until the pressure gets high enough that it starts leaking air (let's say you're sitting on it). If the leak is small, the air coming in around the bball can easily leak out the open window without raising the pressure of the room much...but in an engine, that means the turbo is going to boost more (flapper is closed). So the pressure under the bball is raising. It's leaking more now. The air coming into the room is now enough that the pressure in the room is a bit higher now, but the amount of air entering around the bball is still the same as the amount out the window. And the turbo is still going up in boost. Now, the air is gushing around the bball. The air going out the window at the low room pressure is less than the bball air, so the pressure in the room goes up until it is high enough to force the incoming air out that window. Eventually, the pressure in the room is high enough that it starts opening the WGA. The turbo stops increasing boost and stabilizes at 18...no!...26psi and this house is MOVIN'. We're at full boost in 4th gear for a good 5 seconds, and boy is it windy in that room!

Ahh feels good.

You think the ball leaks in intervals untill the turbo moves enough air to overcome.

I think the ball hold back all pressure untill theres 18PSI infront of it and all at once moves it.

1 reason I think your wrong is....The turbo rises linear in boost. The alterations your describing arent charachteristic of the pressure comming from the turbo. If the turbo is constantly BUILDING boost, then how would it pressureize the ball enough to move it alittle, then allow it to seat again? It would not happen. See?

 

[EclipseTrbo420A]

With ball-and-spring types, a spring-loaded ball is used to block this delivered boost "signal", until the desired boost level is attained. It is at this point, that the delivered boost pressure is strong enough to push the spring-loaded ball toward the spring and out of it's seat, allowing the signal to pass, and reach the Wastegate Actuator.

From boostcontroller.com

 

[kenamond]

Ahh feels good.

You think the ball leaks in intervals untill the turbo moves enough air to overcome.

I think the ball hold back all pressure untill theres 18PSI infront of it and all at once moves it.

1 reason I think your wrong is....The turbo rises linear in boost. The alterations your describing arent charachteristic of the pressure comming from the turbo. If the turbo is constantly BUILDING boost, then how would it pressureize the ball enough to move it alittle, then allow it to seat again? It would not happen. See?

In my scenario, for 18psi boost, the MBC is leaking at 10psi boost, and it doesn't ever close again until you get off the gas. As boost increases, the leak gets worse and worse. Since the vent hole requires more pressure to increase flow out through that little hole, the pressure in the WGA begins rising from 0psi once the MBC first starts to leak. The boost is rising, the leak past the ball is getting worse, and the WGA pressure is rising because it only has a tiny hole to let that increasing inflow of air out. Eventually, boost is 18psi, and the WGA pressure is 8psi, and the flapper opens and boost goes no higher. You continue at full boost for several seconds, and the pressures and flowrate through the MBC are constant.

Think about the vent hole this way. It is not getting bigger. Take a drinking straw and try to blow a certain amount of air per second through it. There is pressure in your mouth to make this happen. Now blow twice that amount of air. To do this, you have to blow harder, and the pressure in your mouth has to be larger. Same with the vent hole. As more air leaks past the ball, the only way the vent hole can leak that same amount of air is for the pressure in the WGA to go up.

 

[kenamond]

With ball-and-spring types, a spring-loaded ball is used to block this delivered boost "signal", until the desired boost level is attained. It is at this point, that the delivered boost pressure is strong enough to push the spring-loaded ball toward the spring and out of it's seat, allowing the signal to pass, and reach the Wastegate Actuator.

From boostcontroller.com

It says "reach the WGA" not "open the WGA". Considering how complicated it is to try to explain this (and understand it), my guess is that A) the person who wrote the description doesn't know what's really going on or B) that person dumbed it down a bit.

 

[EclipseTrbo420A]

In my scenario, for 18psi boost, the MBC is leaking at 10psi boost, and it doesn't ever close again until you get off the gas. As boost increases, the leak gets worse and worse. Since the vent hole requires more pressure to increase flow out through that little hole, the pressure in the WGA begins rising from 0psi once the MBC first starts to leak. The boost is rising, the leak past the ball is getting worse, and the WGA pressure is rising because it only has a tiny hole to let that increasing inflow of air out. Eventually, boost is 18psi, and the WGA pressure is 8psi, and the flapper opens and boost goes no higher. You continue at full boost for several seconds, and the pressures and flowrate through the MBC are constant.

Think about the vent hole this way. It is not getting bigger. Take a drinking straw and try to blow a certain amount of air per second through it. There is pressure in your mouth to make this happen. Now blow twice that amount of air. To do this, you have to blow harder, and the pressure in your mouth has to be larger. Same with the vent hole. As more air leaks past the ball, the only way the vent hole can leak that same amount of air is for the pressure in the WGA to go up.

The hole cant flow enough to regulate boost at 8PSI in the actuator, there for the incomming 18PSI will now take over everthing just like my pic descirbed a page back hold everything at that PSI