X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Sender: To: lml@lancaironline.net Date: Tue, 12 Feb 2008 14:40:18 -0500 Message-ID: X-Original-Return-Path: Received: from [64.12.143.99] (HELO imo-m11.mail.aol.com) by logan.com (CommuniGate Pro SMTP 5.2.0) with ESMTP id 2726296 for lml@lancaironline.net; Tue, 12 Feb 2008 09:28:46 -0500 Received-SPF: pass receiver=logan.com; client-ip=64.12.143.99; envelope-from=Sky2high@aol.com Received: from Sky2high@aol.com by imo-m11.mx.aol.com (mail_out_v38_r9.3.) id q.c0f.1dca49c4 (41811) for ; Tue, 12 Feb 2008 09:28:02 -0500 (EST) From: Sky2high@aol.com X-Original-Message-ID: X-Original-Date: Tue, 12 Feb 2008 09:28:02 EST Subject: Re: [LML] 235/320/360 gear dump valve idea X-Original-To: lml@lancaironline.net MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="-----------------------------1202826482" X-Mailer: Unknown sub 34 X-Spam-Flag: NO -------------------------------1202826482 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable Content-Language: en Larry, =20 Just to review: =20 =20 When the gear is up and the current dump valve is opened, there is a =20 tremendous need to route up fluid to the down side for a second or two. Th= is is=20 because of the spring loaded door actuators and especially for the nose gea= r=20 actuator since the gas spring is exerting an immediate force. The dump val= ve is=20 located near the nose actuator and initially the fluid in the up side of th= e=20 actuator is short circuited to the down side thru the valve. Eventually,=20 demands are made on the pump reservoir because the down side uses more flui= d=20 than the up side (the push rods are outside the chamber when the gear is=20 extended). It is unlikely that the gear would not come down even if initia= lly the=20 pressure had the shuttle valve in the wrong position since the demand to mo= ve=20 fluid is so great. There is no problem with this high priority function of= =20 the current dump valve regardless of the pressure switch conditions. =20 When the gear is down and system pressure builds on both sides (up and down= ,=20 for any reason) such that the pressure switches are both open and the =20 shuttle valve is mis-positioned so that no relief is given on either line. =20= The=20 pump is not started on a request for gear up, so then the dump valve is ope= ned=20 and there is no change because there is no external force being applied to=20= the=20 gear system (all down and locked) and the pressure differential is not grea= t=20 enough to drop the up side switch pressure enough to close the contacts. =20 Consider that the dead band (the pressure range for which the switch remain= s=20 open) of both switches overlap. That is, the lower limit range of the up=20 pressure switch is low enough so that the switch is opened by pressure buil= t up in=20 the system and even the down side won't energize the pump. Also, the switc= h=20 mechanism may also be sluggish or the switch contacts may be a bit burned o= r=20 corroded (no MOV or diode in the relay coil circuit) and that may indirectl= y=20 affect the pressure range for closing the switch. =20 One solution to the latter problem is the 3-position dump valve (off, dump,=20= =20 and up side pressure relief back to the reservoir). Such a solution is mes= sy=20 since the replacement of the dump valve is problematic for those of us that= =20 have full radio stacks. The high pressure line could be tapped for a =20 separate valve in some location that would be more friendly. This valve co= uld be=20 opened and closed as part of every pre-flight check-list. =20 Although this solution resolves the odd occurrence of the pressure problem,=20= =20 it does not address an issue of a failed pressure switch. While a wee =20 Lancair can fly with the gear extended, the 122 KIAS limitation is, uh, a =20 limitation. That is why I suggest a hidden momentary push button switch to=20= bypass the=20 pressure switch for those that regularly experience the problem. Once the=20 pump starts, things should improve. BTW, I do have an accessible bypass sw= itch=20 for the air pressure driven squat switch (also useful on jack stands when=20 doing gear tests). For me, wiring is easier than plumbing. =20 Larry, if you want to whup Mark, consider Randy's install of the ECI cold=20 air intake system.=20 =20 Grayhawk =20 =20 =20 In a message dated 2/12/2008 6:45:32 A.M. Central Standard Time, =20 LHenney@charter.net writes: The dump line goes to the tank and ends submerged in fluid with a =C2=BC= =E2=80=9D down=20 tube in the reservoir. Additionally, in my opinion no fluid would ever tra= vel =20 upstream toward the valve. Thus, no air would be added to the system by us= e=20 of a 3 way vavle. **************The year's hottest artists on the red carpet at the Grammy=20 Awards. Go to AOL Music. =20 (http://music.aol.com/grammys?NCID=3Daolcmp00300000002565) -------------------------------1202826482 Content-Type: text/html; charset="UTF-8" Content-Transfer-Encoding: quoted-printable Content-Language: en
Larry,
 
Just to review: 
 
When the gear is up and the current dump valve is opened, there is a=20 tremendous need to route up fluid to the down side for a second or two. = ;=20 This is because of the spring loaded door actuators and especially for the n= ose=20 gear actuator since the gas spring is exerting an immediate force.  The= =20 dump valve is located near the nose actuator and initially the fluid in the=20= up=20 side of the actuator is short circuited to the down side thru the valve.&nbs= p;=20 Eventually, demands are made on the pump reservoir because the down side=20 uses more fluid than the up side (the push rods are outside the chamber= =20 when the gear is extended).  It is unlikely that the gear would not com= e=20 down even if initially the pressure had the shuttle valve in the wrong posit= ion=20 since the demand to move fluid is so great.  There is no problem with t= his=20 high priority function of the current dump valve regardless of the pressure=20 switch conditions.
 
When the gear is down and system pressure builds on both sides (up and=20 down, for any reason) such that the pressure switches are both open and the=20 shuttle valve is mis-positioned so that no relief is given on either line.&n= bsp;=20 The pump is not started on a request for gear up, so then the dump= =20 valve is opened and there is no change because there is no external force be= ing=20 applied to the gear system (all down and locked) and the pressure differenti= al=20 is not great enough to drop the up side switch pressure enough to close the=20 contacts.  Consider that the dead band (the pressure range for which th= e=20 switch remains open) of both switches overlap.  That is, the lower limi= t=20 range of the up pressure switch is low enough so that the switch is opened b= y=20 pressure built up in the system and even the down side won't energize the=20 pump.  Also, the switch mechanism may also be sluggish or the switch=20 contacts may be a bit burned or corroded (no MOV or diode in the relay coil=20 circuit) and that may indirectly affect the pressure range for closing=20= the=20 switch.
 
One solution to the latter problem is the 3-position dump valve (off, d= ump,=20 and up side pressure relief back to the reservoir).  Such a solution is= =20 messy since the replacement of the dump valve is problematic for those of us= =20 that have full radio stacks.  The high pressure line could be tapped fo= r a=20 separate valve in some location that would be more friendly.  This= =20 valve could be opened and closed as part of every pre-flight=20 check-list.
 
Although this solution resolves the odd occurrence of the pressure prob= lem,=20 it does not address an issue of a failed pressure switch.  While a wee=20 Lancair can fly with the gear extended, the 122 KIAS limitation is, uh, a=20 limitation.  That is why I suggest a hidden momentary push button switc= h to=20 bypass the pressure switch for those that regularly experience the problem.=20= Once=20 the pump starts, things should improve.  BTW, I do have an=20 accessible bypass switch for the air pressure driven squat switch (also= =20 useful on jack stands when doing gear tests).  For me, wiring is easier= =20 than plumbing.
 
Larry, if you want to whup Mark, consider Randy's install of the E= CI=20 cold air intake system. 
 
Grayhawk
 
 
In a message dated 2/12/2008 6:45:32 A.M. Central Standard Time,=20 LHenney@charter.net writes:
<= FONT=20 style=3D"BACKGROUND-COLOR: transparent" face=3DArial color=3D#0000ff size= =3D3>The dump line g= oes to=20 the tank and ends submerged in fluid with a =C2=BC=E2=80=9D down tube in t= he=20 reservoir.  Additionally, in my opinion no fluid would ever travel=20 upstream toward the valve.  Thus, no air would be added to the system= by=20 use of a 3 way=20 vavle.



=
The year's hottest artists on the red carpet at th= e Grammy Awards. AOL Music takes you there.
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