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Ron,
First, The purpose of the Cylinder Head Intake Port Drains are to prevent
hydrostatic lock and flooding. The excess fuel from priming during starting
is vented overboard by the drains.
The check or sniffle valve is left to the airframer to install. It is part
of a TCM installation audit/checklist with a note that a 2 way check
valve(s)is required for turbocharged engines. If it was only a leak it
would not be on issue. Pressurized planes use a "calibrated leak" to supply
air for cabin pressurization but they are upstream of the throttle and use
sonic nozzles to restrict the flow rate. The issue is that the manifold
pressure is below ambient when the turbo is not boosting or all the time in
naturally aspirated engines. The two major issues presented with not using
a check valve on the cylinder head intake port drains are:
1.) Air and dirt are ingested through the open port
2.) Idle speeds are difficult to set with an induction leak
TCM uses two different valves
2 way valve for turbocharged application P/N 640197
1 way valve for naturally aspirated P/N 639486
ERic--
Eric, I have a Cont. TSIO-360 FB in my Turbo Dakota. It has a fuel drain
lines connected to each intake valve pocket. All 6 are teed together under
the engine. I can see no sniffle valve at all. I asked my A&P about this and
he said it's a "calibrated leak" and is not supposed to have a valve. Is
that correct? It bothers me a bit because the engine spits out a fair amount
of fuel from this drain. Seems dangerous and wasteful to me.
Ron Laughlin
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Eric wrote:
Date: Fri, 09 Feb 2001 13:26:28
From: "Eric Parlow" <[EMAIL PROTECTED]>
To: [EMAIL PROTECTED]
Subject: Re: Sniffle valve on IO-550-N (or G)
Message-ID: <[EMAIL PROTECTED]>
Every TCM IO-550-N2B is delivered with a check (sniffle) valve p/n 640197.
ERic-
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