Question for the turbo gurus.

[Will.iam]

I thought upper deck pressure (udp) and manifold pressure were one in the same. Is this not true? I. E. If my turbo waste gate on my tsio-360mb engine keeps my MP at 36” as i climb to 10000ft doesn’t my UDP stay at the same pressure? If i have a leak in the UD manifold will i not effect my MP reading and thus my turbo waste gate woukd compensate for that leak until it was too big of a leak and then i would see the MP drop like when you climb above critical altitude of the turbo charger?

and if UDP is different or not tied to MP how do you check for a leak?

 

[Fly Boomer]

34 minutes ago, Will.iam said:

and if UDP is different or not tied to MP how do you check for a leak?

I'm looking forward to an answer from an expert.

[EricJ]

"Upper deck" pressure is the pressure at the outlet of the turbocharger compressor, which should be consistent to the inlet of the fuel metering device.    There can be a pressure drop across the throttle plate, especially as it closes, and manifold pressure is the pressure after the throttle plate.

So essentially, there is upper deck pressure from the turbocharger to the carbureter/servo/throttle plate, at which point there may be some pressure drop, and then there is manifold pressure.

 

[Tom 4536]

Is there a pressure drop in the intercooler?

[Shadrach]

1 hour ago, Tom 4536 said:

Is there a pressure drop in the intercooler?

I'm not sure but my guess is that no is the short answer.  There is likely a momentary differential during changes in output from the outlet but I would think it would equalize when the system is at a constant power setting.  It is my understanding that upper deck pressure is part of how the fuel servo meters fuel to the engine. UD pressure is at the inlet of the servo and MP is aft of the throttle plate.

[GeeBee]

If UDP pressure were the same as MP, fuel injectors would have a hard time working. Think about it. MP is always has to be lower than the air taken in by the injectors, turbo or non turbo, otherwise, there is no atomization. 

 

[Shadrach]

11 minutes ago, GeeBee said:

If UDP pressure were the same as MP, fuel injectors would have a hard time working. Think about it. MP is always has to be lower than the air taken in by the injectors, turbo or non turbo, otherwise, there is no atomization. 

 

Thanks, I edited my post to be less confusing.

[EricJ]

2 hours ago, Tom 4536 said:

Is there a pressure drop in the intercooler?

Anything that presents a restriction or impedes flow will cause a pressure drop while air is flowing.   Things like intercoolers are designed to present as little restriction as possible for this reason.    So I think "it depends" is probably the right answer, depending on the intercooler and how well it flows.

[kortopates]

UDP is always greater than MAP. In fact, with some of the simpler controllers, UDP is always maintained at a couple inches above redline MAP with sufficient power below or at critical altitude. The big advantage of a modern VAPC (variable automatic pressure controller) used on the later K’s is that the Turbo doesn’t have to work so hard to maintain UDP to deliver redline MAP. So with the VAPC the UDP is just kept a couple inches above MAP.
This also provides a positive enough gradient for the injectors to inject fuel with atomizing air into the cylinders as mentioned above.
But the actual difference between UDP and MAP depends on the type of controller used.


Sent from my iPhone using Tapatalk

[M20F]

 

9 hours ago, Will.iam said:

I thought upper deck pressure (udp) and manifold pressure were one in the same. Is this not true? I. E. If my turbo waste gate on my tsio-360mb engine keeps my MP at 36” as i climb to 10000ft doesn’t my UDP stay at the same pressure? If i have a leak in the UD manifold will i not effect my MP reading and thus my turbo waste gate woukd compensate for that leak until it was too big of a leak and then i would see the MP drop like when you climb above critical altitude of the turbo charger?

and if UDP is different or not tied to MP how do you check for a leak?

 

What problem are you trying to solve? 

[Will.iam]

My fuel flow is dropping off as i climb where it used to not. Since my MP stays at 36” consistently this is causing my cylinders to “lean out” during the climb. Started at 500msl and 24.1 ff by the time i got to 6500ft msl my ff was 22 which is too low for 36” mp. So my cylinder temps got up to 382 when they stay below 360. My A&P says i have a pressure leak at the UDP and that’s where I’m confused as i would think if the leak was enough to change the FF it would also drop the MP reading too but I don’t know. Will let him run with this diagnosis but i wonder how he is going to find that leak if the only guage i have is a MP gauge. 

https://apps.savvyaviation.com/flights/5837204/b7a311a3-596e-4d1d-8547-d7963f242852

there is the savvy link from 8 mins to 17 mins is the full power climb to 6500ft. You can see the FF slowly rolling back from 24 to 22.  It should not do this so now the question is why. First check is for leaks so we will see. Hopefully that cures it. The fuel pump spider valve and throttle body were freshly overhauled. I really hope it’s not setup wrong and we have to send it back. Blah. 

[EricJ]

10 minutes ago, Will.iam said:

My fuel flow is dropping off as i climb where it used to not. Since my MP stays at 36” consistently this is causing my cylinders to “lean out” during the climb. Started at 500msl and 24.1 ff by the time i got to 6500ft msl my ff was 22 which is too low for 36” mp. So my cylinder temps got up to 382 when they stay below 360. My A&P says i have a pressure leak at the UDP and that’s where I’m confused as i would think if the leak was enough to change the FF it would also drop the MP reading too but I don’t know. Will let him run with this diagnosis but i wonder how he is going to find that leak if the only guage i have is a MP gauge. 
https://apps.savvyaviation.com/flights/5837204/b7a311a3-596e-4d1d-8547-d7963f242852

there is the savvy link from 8 mins to 17 mins is the full power climb to 6500ft. You can see the FF slowly rolling back from 24 to 22.  It should not do this so now the question is why. First check is for leaks so we will see. Hopefully that cures it. The fuel pump spider valve and throttle body were freshly overhauled. I really hope it’s not setup wrong and we have to send it back. Blah. 

TCM injection systems have a bunch of interdepencies that can create strange problems.   My experience with them is very limited, but there's an aneroid at the fuel pump that might do something like that.    This article suggests that Merlin waste gates (if you have that) are sensitive to upper deck pressure and can affect fuel flow, so your A&P may be on to something that a leak there could be affecting fuel.   If your A&P has experience with turbo'ed TCM systems, he may be on the right trail.    There are also a number of folks here that are very familiar with the details of these systems, so I am anticipating some useful insights. 

http://www.kellyaerospace.com/articles/ContinuousFlow.pdf

[Will.iam]

3 minutes ago, EricJ said:

TCM injection systems have a bunch of interdepencies that can create strange problems.   My experience with them is very limited, but there's an aneroid at the fuel pump that might do something like that.    This article suggests that Merlin waste gates (if you have that) are sensitive to upper deck pressure and can affect fuel flow, so your A&P may be on to something that a leak there could be affecting fuel.   If your A&P has experience with turbo'ed TCM systems, he may be on the right trail.    There are also a number of folks here that are very familiar with the details of these systems, so I am anticipating some useful insights. 

http://www.kellyaerospace.com/articles/ContinuousFlow.pdf

Merlin waste gate is not an automatic controller. I. E. You set 30” mp then climb 5000 ft you will be at a lower MP your arm has to be the actuator and re adjust the pressure back up to 30” by adding more throttle thats why with merlin controller you can’t shove the throttle to the firewall because the engine will over boost. My waste gate controller is fully automatic. I can and do shove the throttle to the firewall on every takeoff and the wastegate controls the the turbo pressure to keep my manifold at 36” all the way to 24,000 at which time I’m at full wastegate closed and all exhaust is going through the turbo and turbo is outputting maximum pressure if i climb any higher my MP then starts to drop off like a NA engine would but it’s starting it’s drop off at 36” thus being fully automatic if there was a leak lowering the pressure at the udp it should i think lower the mp but then the turbo would offset that lower MP by increasing more boost. Which it’s doing in the climb to 6500ft i lost no MP it stayed steady at 36” pressure which should have told the fuel pump to stay steady with ff at 24 to match the 36”. Maybe the shop setup the fuel pump to an LB specification instead of an MB specification as it came back set at 22gph when we did the static runup and had to adjust the fuel pump to 24.7 which it now does at 500msl but doesn’t hold it there through the climb  

[Will.iam]

8 hours ago, EricJ said:

TCM injection systems have a bunch of interdepencies that can create strange problems.   My experience with them is very limited, but there's an aneroid at the fuel pump that might do something like that.    This article suggests that Merlin waste gates (if you have that) are sensitive to upper deck pressure and can affect fuel flow, so your A&P may be on to something that a leak there could be affecting fuel.   If your A&P has experience with turbo'ed TCM systems, he may be on the right trail.    There are also a number of folks here that are very familiar with the details of these systems, so I am anticipating some useful insights. 

http://www.kellyaerospace.com/articles/ContinuousFlow.pdf

Thanks for the troubleshooting link very informative. 

[Fly Boomer]

12 hours ago, kortopates said:

on the later K’s is that the Turbo doesn’t have to work so hard to maintain UDP to deliver redline MAP. So with the VAPC the UDP is just kept a couple inches above MAP

Is this true for the TSIO-520-NB in a Rocket?

[N231BN]

If your MP is constant then the UDP is not changing. Does the -MB have a fuel pressure regulator? I haven't worked on a 252 but the TSIO-520s in twin Cessna's have a separate device called that and it changes the setup procedure.

Also, make sure the UDP sense line to the fuel pump is secure and not leaking. If it is a stainless line the alignment needs to be perfect on the flare.