X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Sender: To: lml@lancaironline.net Date: Sat, 17 May 2014 11:41:04 -0400 Message-ID: X-Original-Return-Path: Received: from nm24-vm0.bullet.mail.bf1.yahoo.com ([98.139.213.161] verified) by logan.com (CommuniGate Pro SMTP 6.0.9e) with ESMTPS id 6876476 for lml@lancaironline.net; Fri, 16 May 2014 13:34:35 -0400 Received-SPF: pass receiver=logan.com; client-ip=98.139.213.161; envelope-from=chris_zavatson@yahoo.com Received: from [98.139.212.152] by nm24.bullet.mail.bf1.yahoo.com with NNFMP; 16 May 2014 17:33:59 -0000 Received: from [98.139.212.218] by tm9.bullet.mail.bf1.yahoo.com with NNFMP; 16 May 2014 17:33:59 -0000 Received: from [127.0.0.1] by omp1027.mail.bf1.yahoo.com with NNFMP; 16 May 2014 17:33:59 -0000 X-Yahoo-Newman-Property: ymail-3 X-Yahoo-Newman-Id: 611600.26546.bm@omp1027.mail.bf1.yahoo.com Received: (qmail 85565 invoked by uid 60001); 16 May 2014 17:33:59 -0000 X-YMail-OSG: A.tuZOIVM1nh28L45OIFI8lK8CQXMS97WCM36cPRj7Y5HNZ DdRS7rDAogkw0tcRrdBv2_HIm8sNb51pI4zKjXgHY.aDmWK5e5a.g_YI85Iq JUGgrx7gvoRtg22gBo.aXTH_.iWnPIojWKoIPQN_pmmEv_DeWzrECjQtGF0T TT514npZKYowzfJQiZNii5wBUg8cgM3t2QDL2EbEw5mhmSPNPhXE7J5e0teF zOKfFsSDa4rjiP2Wr67NMCRyn1G72aN2zTb9q9SQDUNQ5dcG5s7__UOOeRp9 rqsOrx4Nt1BHWKjh7ctexE3aWuyetHdO0DPBVvtFXt4PZdAGHkv2bPNs5ToM f0W7TO9e3K_6rJ86LlZ7akyuKtAfF_Fq1NikMqg6I2SS.jqnDH7V6dwfRhNZ L5SsP8_6ZDWMySStFAEpVj978tHJiLeHwVvd4anIUqPLo_2YHtTgp_umPfoC ruk6SEZHhgkI2YmnRHJ2dD_MiJ.eRsYbyBsxwLUgd8ccbDH7k32N8FIVMr6E n.7yjgxArguVf1Dlfz4U4zU8hlpyizBfT31aNBi6obC5KsK9tRt9EY4wiUHc UNB20Bjr25cvSCqPfWXzySQgodn0Ld8FwoYAEb9ADHtFxPQb._5863glq2b. RofqKwnGgKup33hHrXkBBCglToQlQVm07szmCFg-- Received: from [172.14.16.72] by web161206.mail.bf1.yahoo.com via HTTP; Fri, 16 May 2014 10:33:59 PDT X-Rocket-MIMEInfo: 002.001,V29sZmdhbmcsClRleHRib29rIGV4YW1wbGVzIGFyZSBvZnRlbiBvdmVyc2ltcGxpZmllZCBhbmQgZmFsbCBzaG9ydCB3aGVuIGFwcGxpZWQgaW4gdGhlIHJlYWwgd29ybGQuwqAgCgoiLiAuIC4gd2hlbiB5b3Ugc3RhcnQgdG8gcHVzaCB5b3VyIGNhciB5b3UgaGF2ZSB0byAgYXBwbHkgYSBsb3Qgb2YgcHJlc3N1cmUgCi4gLiAuIGJ1dCBsZXNzIHByZXNzdXJlIHRvIGtlZXAgaXQgIHJvbGxpbmcuIgoKWW91ciBjYXIgZXhhbXBsZSBsZWF2ZXMgb3V0IGNyaXRpY2FsIGV4dGVybmFsIGZvcmNlcyBhY3Rpbmcgb24BMAEBAQE- X-Mailer: YahooMailWebService/0.8.188.663 References: X-Original-Message-ID: <1400261639.39553.YahooMailNeo@web161206.mail.bf1.yahoo.com> X-Original-Date: Fri, 16 May 2014 10:33:59 -0700 (PDT) From: Chris Zavatson Reply-To: Chris Zavatson Subject: Re: Hydraulic Pressure Spike Video X-Original-To: LML posts In-Reply-To: MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="1938299484-495300502-1400261639=:39553" --1938299484-495300502-1400261639=:39553 Content-Type: text/plain; charset=iso-8859-1 Content-Transfer-Encoding: quoted-printable Wolfgang,=0ATextbook examples are often oversimplified and fall short when = applied in the real world.=A0 =0A=0A". . . when you start to push your car = you have to apply a lot of pressure =0A. . . but less pressure to keep it = rolling."=0A=0AYour car example leaves out critical external forces acting= on the system.=A0 =0AThis 'car' has a massive compressed spring sitting be= hind it and=A0the car=A0pointed downhill.=A0 When you let it go, you don't = have to push it, it pulls you=A0- and=A0with a big jolt.=A0=0ADuring extens= ion, the pump is not having to apply any pressure or do any work to get the= gear down.=A0 Note that the gauge went back down to zero after the spike.= =A0 =0AIf you observe the=A0retraction sequence (I know you need a plane fi= rst) you'll see a completely different picture.=A0 To get the gear up, the = pump has to do work.=A0 Pressure=A0will come up=A0to about 500 psi and stay= there while the gear is in transit.=0A=0AThe risk with the extension press= ure spike is that it can push the spool backward=A0and close off the poppet= valve.=A0 When this happens everything stops.=A0 The system cannot relieve= pressure on its own because the poppet valve has closed and the pump has s= topped running.=A0 You will see equal pressures in both circuits with the g= ear partially extended.=A0 =0A=0AIn order to observe this first hand,=A0I s= uggest getting=A0a hold of a 320/360, installing some pressure gauges and d= oing a couple hundred landings in different temperature conditions.=A0 You = can then raise and lower the low-side pressure=A0set-point and observe the = relation ship between low side pressure setting and near-miss hesitations a= nd the full lock-ups.=A0 You'll also see how these are affected by OAT and = initial high side pressure.=0AThe hesitations are sort of a quick Start-Sto= p-Start with the gear continuing all the way down.=A0=A0During a=A0full loc= k-up you'll hear the pump start up for just a fraction of a second.=A0 You'= ll hear the gear drop from the wells and then all goes silent.=A0=A0A quick= glance at the pressure gauges will show ~600 psi (stock set-point) in both= high and low circuits.=0A=0AChris Zavatson=0AN91CZ=0A360std=0Awww.N91CZ.ne= t=0AOn Friday, May 16, 2014 7:42 AM, Wolfgang wrote:= =0A =0A=0A=0AOf course there's a pressure spike. Standard in all =0Ahydrau= lic systems. =0AThat's what happens when you start pumping fluid =0Afaster= than the inertia of the gear can follow. =0A=A0 =0AThink about it =0A. . = . when you start to push your car you have to =0Aapply a lot of pressure = =0A. . . but less pressure to keep it =0Arolling. =0A=A0 =0ASo the pressure= spike can open up the switch =0A. . . fine =0A. . . then the pressure ge= ts relieved as the gear =0Astarts to move =0A. . . and the switch closes a= gain =0A. . . and the motor runs again =0A. . . until the real end of str= oke makes the =0Apressure go high and stay hi holding the pressure switch o= pen. =0A=A0 =0AThis is a non-problem. . . . let it go =0Aalready. =0A=A0 = =0AWolfgang =0A=A0 =0A----- Original Message ----- =0A>From: Chris Zavats= on =0A>Sent: Thursday, May 15, 2014 7:33 =0AAM =0A>Subject: Hydraulic Pres= sure Spike Video =0A>=0A> =0A>Using my iPhone I took a video of my pressur= e gauges while extending my gear on a flight today.=A0 It is starting to w= arm up out here.=A0=A0We're not cooking yet, but it is enough to start obs= erving the hydraulic pressure spike which was the subject of a previous LM= L thread. =0A>It was a bit bumpy on downwind, but the gauges are still cle= arly visible in the video. =0A>The high pressure circuit was just a hair u= nder 1,500 psi when gear-down was selected.=A0 One can hear the pump fire = up and release the gear,=A0 The high side pressure begins to drop and then= the spike immediately hits the low side. It reached 450 psi in this clip.= =A0 If the spike reaches the low side pressure switch setting, the pump so= lenoid will open and the pump will shut down.=A0 I have my low side pressu= re switch set to 800 psi which has proven to be high enough to avoid any g= ear hesitations and/or extension failures. =0A>=0A> =0A>http://n91cz.com/H= ydraulics/GearExtensionPressureSpike.mp4=A0=A0=A0 (hi res 16Mb) =0A>http:/= /n91cz.com/Hydraulics/GearExtensionPressureSpike-lores.mp4=A0=A0 (lo res 3= Mb) =0A>=0A> =0A>Chris Zavatson =0A>N91CZ =0A>360std =0A>www.N91CZ.net =0A>= =0A> --1938299484-495300502-1400261639=:39553 Content-Type: text/html; charset=iso-8859-1 Content-Transfer-Encoding: quoted-printable
Wolfgang,<= /span>
Textbook examples are often oversimplified and= fall short when applied in the real world. 

". . . when you start t= o push your car you have to apply a lot of pressure
. . . but less pressure to keep it rolling."

Your car example leav= es out critical external forces acting on the system. 
During extension, the pump is not having to apply any pressure or do any w= ork to get the gear down.  Note that the gauge went back down to zero after the spike. 
If you observe the retraction= sequence (I know you need a plane first) you'll see a completely different= picture.  To get the gear up, the pump has to do work.  Pressure=  will come up to about 500 psi and stay there while the gear is i= n transit.

The risk with the ext= ension pressure spike is that it can push the spool backward and close= off the poppet valve.  When this happens everything stops.  The system cannot relieve pressure on its own because the poppet valve has clo= sed and the pump has stopped running.  You will see equal= pressures in both circuits with the gear partially extended.  =

In order to observ= e this first hand, I suggest getting a hold of a 320/360, install= ing some pressure gauges and doing a couple hundred landings in different t= emperature conditions.  You can then raise and lower the low-side pres= sure set-point and observe the relation ship between low side pressure= setting and near-miss hesitations and the full lock-ups.  You'll also see how these are affected by OAT and initial high side = pressure.
The hesitations are= sort of a quick Start-Stop-Start with the gear continuing all the way down= .  During a full lock-up you'll hear the pump start up for j= ust a fraction of a second.  You'll hear the gear drop from the wells = and then all goes silent.  A quick glance at the pressure gauges = will show ~600 psi (stock set-point) in both high and low circuits.<= /span>

Chris Zavatson
N91CZ
360std
www.N91CZ.net
On Friday, May 16, 2014 7:42 AM, Wolfgang <Wolfgang@MiCom.n= et> wrote:


<= style>
=0A
Of course there'= s a pressure spike. Standard in all =0Ahydraulic systems.
=0A<= div>That's what happens when you start pump= ing fluid =0Afaster than the inertia of the gear can follow.
= =0A
 
=0A
Think about it
=0A
. . . when you start to push your car you have to =0Aapply= a lot of pressure
=0A
. .= . but less pressure to keep it =0Arolling.
=0A
 
=0A
So the pressure spike can open up the switch =0A
=0A. . . fine
=0A
. . . then the pressure gets relieved as the gear =0A= starts to move
=0A
. . . a= nd the switch closes again
=0A
. . . and the motor runs again
=0A
. . . until the real end of stroke makes the =0Apressure go= high and stay hi holding the pressure switch open.
=0A
 
=0A
This is a non-problem. . . . let it go =0Aalready.=0A
 
=0A
Wolfgang
=0A
 
=0A
=0A
----- Original Message -= ----
=0A
From: =0A= Chris =0A Zavatson
=0A
S= ent: Thursday, May 15, 2014 7:33 =0AAM
=0A
Subject:= Hydraulic Pressure Spike =0A Video
=0A

=
=0A
=0A
Using my iPhone I took a video of my pressure gauges while = extending my =0A gear on a flight today.  It is starting to warm up o= ut =0A here.  We're not cooking yet, but it is enough to start o= bserving =0A the hydraulic pressure spike which was the subject of a previ= ous LML =0A thread.
=0A
It was a bit bumpy on downwind, but the= gauges are still clearly visible =0A in the video.
=0A
The hig= h pressure circuit was just a hair under 1,500 psi when gear-down =0A was = selected.  One can hear the pump fire up and release the gear,  = =0A The high side pressure begins to drop and then the spike immediately h= its the =0A low side. It reached 450 psi in this clip.  If the spike = reaches the low =0A side pressure switch setting, the pump solenoid will o= pen and the pump will =0A shut down.  I have my low side pressure swi= tch set to 800 psi which has =0A proven to be high enough to avoid any gea= r hesitations and/or extension =0A failures.
=0A

=0A =0A =0A
=0A
Chris Zavatson
=0A
N91CZ
= =0A
360std
=0A
www.N91CZ.net
=0A



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