From: ReganRanch@aol.com
Message-ID: <7308ed98.36221af7@aol.com>
Date: Mon, 12 Oct 1998 11:06:31 EDT
To: lancair.list@olsusa.com
Subject: Hydraulics
Mime-Version: 1.0

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In a message dated 98-10-12 01:23:20 EDT, you write:

<< And for Brent, many thanks for designing the flaw out of my IV-P's
 hydraulic system.  But please tell me you had nothing to do with
 mounting the reservoir to the pump by running a bolt through the
 bottom of the resivour, and then modifying that installation with a
 stud.  Ever try to seal a stud against hydraulic leakage with an "O"
 ring? >>

Several of you have asked what the flaw was. The fatal flaw was using 4-way
solenoid operated spool valves to actuate both the gear and the flaps in a
hydraulic system without a filter. YST, spool valves don't have elastomeric
(rubber) seals so they rely on a precision fit, typically between .0003 and
.0005 inches, between sliding parts to control crossflow. Unfortunately this
is a perfect spot to wedge some dirt or a drill cap or a metal chip or a
sliver od paper or a thread from a rag or anything else in the universe bigger
than 1/10 the width of a human hair.

Having used these very valves before I was keenly aware of their shortcomings.
I would never use them on my plane. I asked Lance "How many gear up landings
due to hydraulic system failures are acceptable?" His answer was the right one
"None" he said. I handed him one of the rotary plate valves we use now and
said "Use these, they are more reliable, simpler, seal better, resist
contamination AND they are cheaper!" I think the last one sold the program.
The down side is the Hydraulic Controls salesman took me off his X-Mass card
list, but hey, you can't keep everyone happy.

As to the through bolt in the reservoir, ouch. When I received my reservoir
the poor O-ring had already given up the fight and was half extruded from
under the washer. I got a new O-ring that was a close fit to the bolt and then
chamfered an aluminum washer deep enough to hold all but about .015" of the O-
ring. The object is to have the washer take the tension load of the bolt and
the O-ring to be compressed against the bolt and the tank. Hasn't had a leak
since.

Regards
Brent