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Date: Thu, 04 Feb 2010 22:16:28 -0500
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Subject: Re: [LML] Re: Airspeed sensing switch: Pressurization (IV-P)
From: paul miller <paul@tbm700.com>
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References: <list-4109252@logan.com>

Pardon my ignorance of the 4P system but I could not find a schematic to =
reference.   I assume you have only the one outflow valve and not the =
secondary.   Taping over the outflow valve and not seeing a dramatic =
change in cabin differential suggests leakage elsewhere.  In the twins =
we would reverse a vacuum cleaner into the cabin through a makeshift =
connection and pressurize the aircraft.  It takes a while to fully fill =
the cabin but you get a good differential from a shop-vac or other =
device.   Of course, it is very dangerous to do this and such a =
connection must be done with all the safety precautions to prevent =
decompression or other problems while on the ground such as opening a =
pressurized vessel.   However, it was revealing where the whistles came =
from and perhaps this type of test could help isolate where the =
problem(s) lies.   =46rom this thread I am assuming the turbo is =
operating and the slope controller is working too.  It sounds like those =
components are working correctly.   I would have first suspected the =
outflow valve not fully closing but you covered it up and took it out of =
the loop.  =20

Paul
N357V L2K
=20
On 2010-02-03, at 7:42 AM, Jeffrey Liegner, MD wrote:

> I have flown with the Duke's Valve completely occluded via duct tape =
fully across the rear seat opening (for several month, in fact, part fo =
an experiment).  I was ready to puncture the tape if needed.  The cabin =
did not over pressurize, but it would have above ~13,000' to ~15,000' =
during power climb.  The initial slam of higher pressure during power up =
and take off was noticible, but not in excess of 3psi (it was just =
immediately noted).  Over pressurization at anytime was avoided with a =
controlled reduction of the throttle (MAP) to demonstrate cabin pressure =
correlation to MAP.  Upon landing, with outflow still occluded, cabin =
was always at airport ambient pressure before door seal was dropped.  =
Again, this zero differential is notable on short final, door seal =
tight, Duke's outlet occluded, engine below 11.5".
>=20
> During flight, outlet occluded, a small puncture through the occluding =
tape demonstrated brisk exiting air through the puncture out the Duke's =
Valve, but without a rapid cabin decompression (like one might =
experience with door seal deflation).  At any altitude, door seal =
deflation results in immediate cabin decompression and cabin climb to =
current flying altitude.
>=20
> I also have a cabin alert above 10,000' and panel light notification.
>=20
> Jeff L