" . . . you can only override one pressure switch at a time or overload the system.
You need one switch each for the up and down. In the event of a problem you have to make sure you push the right switch"...
Overload what exactly? The gear selector determines which pressure switch is powered. If you jumper across an unpowered switch, nothing happens.
While I do not advocate putting in switches to mask a pump problem that should really be investigated and fixed at the source, momentary switches have other benefits.
1. Checking the relief valve settings in the pump. By holding down the switch, one can see the relief valve setting of the pump.
2. Back-up for a failed pressure switch. This was more common with the VEP switches, but current version is not immune.
3. Recharging the system on demand - The hysteresis loop on the pressure switches is quite large. The gear can start to sag before the pressure switch recharges the system. This is more of an issue for the Outback Gear due to the higher aerodynamic loads pulling on the gear.
With automation and complexity come new failure modes. Give the pilot enough information about the state of the aircraft systems to figure out what happened and enough controls to solve the problem.
Last summer when the high pressure switch went out, the pump shut off before the gear was all the way up. Higher than normal air noise was the first clue. A quick look at the pressure gauges revealed the high side at only 800 psi. The momentary switch pulled the gear the rest of the way up. Examination of the pressure switch uncovered intermittent electrical contact within the switch when pressurized.
Chris Zavatson
N91CZ
360std
From: Wolfgang <Wolfgang@MiCom.net>
To: lml@lancaironline.net
Sent: Monday, February 20, 2012 4:58 AM
Subject: [LML] Re: 320/360 Hydraulic Pressure Switch
Yes, that would be easy . . . except . . . you can only override one pressure switch at a time or overload the system.
You need one switch each for the up and down. In the event of a problem you have to make sure you push the right switch.
If you come up with some
more complicated wiring, you could make it work with only one switch for both up and down but you still have to push the button if something isn't working as required.
. . . or . . . you could put in a completely automatic system . . .
Wolfgang
----- Original Message ----- From: "Greenbacks, UnLtd." <
N4ZQ@VERIZON.NET>
To: <
lml@lancaironline.net>
Sent: Friday, February 17, 2012 1:07 PM
Subject: Re:320/360 Hydraulic Pressure Switch
Seems to me the simplest and least expensive option would be to install a momentary on switch in the cockpit to override and close the open pressure switches.
Just my 2 cents.
Angier Ames
N3ZQ
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