X-Virus-Scanned: clean according to Sophos on Logan.com X-SpamCatcher-Score: 50 [XX] Return-Path: Sender: To: lml@lancaironline.net Date: Tue, 17 Apr 2007 23:10:52 -0400 Message-ID: X-Original-Return-Path: Received: from smtp4.na.baesystems.com ([63.164.202.13] verified) by logan.com (CommuniGate Pro SMTP 5.1.8) with ESMTP id 1990688 for lml@lancaironline.net; Tue, 17 Apr 2007 22:17:32 -0400 Received-SPF: none receiver=logan.com; client-ip=63.164.202.13; envelope-from=Christopher.Zavatson@baesystems.com Received: from smtp2.na.baesystems.com (smtp2.na.baesystems.com [10.40.96.13]) by smtp4.na.baesystems.com (8.13.6/8.13.6) with ESMTP id l3I3G2vG016482 for ; Tue, 17 Apr 2007 23:16:02 -0400 (EDT) Received: from GLDMS00006.goldlnk.rootlnka.net ([10.44.64.12]) by smtp2.na.baesystems.com (8.13.6/8.13.6) with ESMTP id l3I2GXif008100 for ; Tue, 17 Apr 2007 22:16:37 -0400 (EDT) Received: from gldms10602.goldlnk.rootlnka.net ([10.64.39.19]) by GLDMS00006.goldlnk.rootlnka.net with Microsoft SMTPSVC(6.0.3790.1830); Tue, 17 Apr 2007 22:16:33 -0400 Received: from GLDMS10607.goldlnk.rootlnka.net ([10.64.39.20]) by gldms10602.goldlnk.rootlnka.net with Microsoft SMTPSVC(6.0.3790.1830); Tue, 17 Apr 2007 19:16:32 -0700 X-MimeOLE: Produced By Microsoft Exchange V6.5 Content-class: urn:content-classes:message MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----_=_NextPart_001_01C7815F.9462D90A" Subject: RE: [LML] Re: Gear Trouble X-Original-Date: Tue, 17 Apr 2007 19:16:31 -0700 X-Original-Message-ID: In-Reply-To: X-MS-Has-Attach: X-MS-TNEF-Correlator: Thread-Topic: [LML] Re: Gear Trouble Thread-Index: AceBVhtlfVSA5JArTJKlBiZWOSTLoAABRXDg References: From: "Zavatson, Christopher J \(US SSA\)" X-Original-To: "Lancair Mailing List" X-OriginalArrivalTime: 18 Apr 2007 02:16:32.0487 (UTC) FILETIME=[94FD8F70:01C7815F] This is a multi-part message in MIME format. ------_=_NextPart_001_01C7815F.9462D90A Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: quoted-printable =09 <> Randy, The 'gear won't go down problem' is different than the 'gear won't go up' in a number of ways. Many discussions prior to this thread have dealt with the gear not extending. I thought we were discussing the gear not retracting, but your comments above refer to the gear not extending. The system is not symmetrical so problems in one direction will not replicate in the other. The spool valve only opens a low resistance path for the down circuit and gravity is a factor that affects the two directions differently. In the down direction gravity actually hurts us and can be the cause of failures to extend. Gravity acting on all the undercarriage acts as a bank of spring loaded piston pumps that can shove the spool valve back in the wrong direction just long enough to trip the low pressure switch thus shutting down the real pump. =20 In the case you just described with pressure in both circuits, is there pressure on both sides prior to selecting down or just after you select down. The situation I described above occurs just after the gear is selected down. Oftentimes it is perceived as just a pump hesitation and gear comes out on its own and occasionally everything goes quite. As I recall there was some unique history to your pump(s). With the current design (and the correct spool valve orientation) when the high side is pressurized it opens a low resistance path from the low side to the reservoir. The low side simply cannot maintain pressure. (see Parker schematic for details) This functionality of the spool valve is not needed to get the gear up and down, but it does allow retraction with less work on the part of the pump and more importantly for us it prevents both sides from pressurizing while the gear is retracted. =20 =20 <> =20 Bob, In the failure to extend case with pressure on both sides, opening the dump valve allows gravity to relieve pressure by removing rod volume from the hydraulic circuit. It wouldn't work if our cylinders needed to retract to get the gear out. In that case we would need to open the stuck circuit to the atmosphere or reservoir Chris Chris Zavatson N91CZ 360std www.N91CZ.com ------_=_NextPart_001_01C7815F.9462D90A Content-Type: text/html; charset="us-ascii" Content-Transfer-Encoding: quoted-printable

<<I=20 don't know if the problem is from a spool valve, this is the second = pump=20 I've had in my plane and both have done the same thing in warmer = weather.=20 And, of course, being in southern California it's=20 usually always on the warm side.

I=20 can see on the gear pressure gauge that as the heat goes up so does = the=20 pressure. It's gets to a point where the pressure opens both = pressure=20 switches, so when I switch to gear down there's no connection. One = small tap=20 on the dump valve and it releases the excess pressure on the low = side and=20 the pump lites up.>>

Randy,

The=20 'gear won't go down problem' is different than the 'gear won't go up' = in a=20 number of ways.  Many discussions prior to this thread have dealt = with=20 the gear not extending.  I thought we were discussing the gear = not=20 retracting, but your comments above refer to the gear not=20 extending.  The system is not symmetrical so problems in one = direction=20 will not replicate in the other.  The spool valve only opens a = low=20 resistance path for the down circuit and gravity is a factor that = affects=20 the two directions differently.  In the down = direction gravity=20 actually hurts us and can be the cause of failures to extend.  = Gravity=20 acting on all the undercarriage acts as a bank of spring loaded = piston=20 pumps that can shove the spool valve back in the wrong direction = just=20 long enough to trip the low pressure switch thus shutting down the = real=20 pump.

 

In=20 the case you just described with pressure in both circuits, is there = pressure=20 on both sides prior to selecting down or just after you select = down. =20 The situation I described above occurs just after the gear is = selected=20 down.  Oftentimes it is perceived as just a pump hesitation and = gear=20 comes out on its own and occasionally everything goes = quite.  As I=20 recall there was some unique history to your pump(s).  With the = current=20 design (and the correct spool valve orientation) when the high side is = pressurized it opens a low resistance path from the low side to the=20 reservoir.  The low side simply cannot maintain pressure.  = (see=20 Parker schematic for details) This functionality of the spool valve is = not=20 needed to get the gear up and down, but it does allow retraction with = less=20 work on the part of the pump and more importantly for us it prevents = both=20 sides from pressurizing while the gear is retracted.

 

 

<<I don't = understand this=20 analysis.   If the system pressure is high enough to hold = both=20 pressure switches open, how would opening the dump valve release the = excess=20 pressure?>>

 

Bob,

In the failure to extend = case with=20 pressure on both sides, opening the dump valve allows gravity to = relieve=20 pressure by removing rod volume from the hydraulic circuit.  It = wouldn't=20 work if our cylinders needed to retract to get the gear out.  In = that=20 case we would need to open the stuck circuit to the atmosphere or=20 reservoir

Chris

Chris = Zavatson
N91CZ
360std
www.N91CZ.com
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