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Pressure Switches



I've had the pleasure (?) of setting up 4 RG systems now. I have yet to
use a pressure gauge for any of them. I have had to adjust about every
one of them to pull the gear up. I don't recall ever adjusting a low
pressure side switch for getting the gear to extend.

All,

First, yes, we have had a few defective switches. I've replaced or
exchanged 6 -8 of them since I came to work with Velocity. My comments
below are in reference to the pros and cons of Hyd. pressure gauges.

The only systems that I have heard about hydraulic line / pump / actuator
failure or poor operating conditions has been due to the following items,
none of which were exclusively pressure related.

1)	Improper flaring of the line (knock on wood...hasn't happened
to me! (yet!) ) and use of soft aluminum tubing instead of the hardwall
tubing (OK, I got in a hurry and grabbed the first piece of 1/4" line
close by to make a repair!) causing the line to blow out of the "B" nut
and sleeve. Trust me...what a mess!

2)	material contaminents in the hydraulic fluid damaging "O"
rings.

3) 	not totally bleeding the air out of the system.

While I don't reccomend cranking the switches down to the stops and the
pressure be damned, I have not ever worried about it. But then again I
have never cranked  them to the stops to get the system working. I would
be checking other things pretty quick after the first two or three small
adjustments. Now if the gear were to go up a little with the first
adjustment, a little more with the second, a little more with the third,
I'd recycle the gear down then back up to see what happens. If I needed
one more adjustment, so be it. Any more though and I'd be checking for
friction induced restrictions in the system.

For example, I have seen pivot bolts in the nose gear linkage too tight.
Half a turn to loosen them and everything worked fine. Those pivot bolts
only have shear load on them, they don't need to be torqued way down.
This usually shows up in the freefall overcenter locking test.

I guess if Velocity published a definitive (example only!) 550 psi low
side / 1000 psi high side, I (we) would spend a good deal of time trying
to figure out why some guys gear wouldn't retract until it was set for
1150 psi. We'd even have to answer calls from somebody  that would ask if
the gear retracted at 875 psi, is that a problem? Do I need to go ahead
and set it up to 1000 psi? 

Bottom line for me personally is, if it works, it works. If it doesn't, I
find out why and fix it. Also, out of all of the RG's out there, I'd bet
fewer than 15% have gauges in them.  Once they system is in and working,
what does the gauge really tell you? The gear will let you know if the
hydraulic system is loosing pressure. Even if you see this on the
hydraulic gauge in flight, your gear is still going to creep out of the
wells. If your pump is cycling, you'll hear it...don't need a gauge for
that. In any case, not much one can do to remedy the situation from the
cockpit without disabling the hydraulic system (pull the CB).

My Personal opinion? It is just one more thing in the panel to draw my
attention from the really important things that my staying airborne are
dependent on. Oil pressure for one! 

Martin

What the heck...I'll flog this horse one more time...why not have an SWR
meter the panel so that you continually know what the status is of your
radio? Just a thought!

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