From: RWolf99@aol.com
Message-ID: <50.7c6737d.2698296c@aol.com>
Date: Sat, 8 Jul 2000 02:51:24 EDT
Subject: Re:  Pressure Switches
To: lancair.list@olsusa.com, olsen@eai.com
Reply-To: lancair.list@olsusa.com
Mime-Version: 1.0

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Dan -

Make sure the switches are bad before you change them out.  I'd do this by 
taking an ohmmeter and determining whether the switches are normally open or 
closed with no pressure on them.  

Now, given that it's midnight and I'm not thinking too clearly...

To test the high pressure switch--
If normally open at zero pressure, then run the gear up and short across the 
switch at the relay to mimic a switch closure, and verify the motor turns 
off.  If normally closed at zero pressure, then run the gear up and pull the 
wire off the relay (disconnecting the switch) and verify the motor turns off. 
 What you've just done is verify that it's all wired properly, since you've 
just "forced" a switch closure.  Actually, you haven't really tested the 
switches at all -- the system might just not be coming up to full pressure.

If it is, in fact, wired properly (mine wasn't, by the way, the first time I 
tried it) then you have one of two possible problems.  The switch is bad or 
the system never gets up to pressure.  The system may not get up to pressure 
for several reasons.  One, you may have a huge leak somewhere.  I assume 
you're not pissing hydraulic fluid all over your shop, so such a leak would 
probably be internal to a cylinder (like, it's missing an O-ring).  Also, the 
motor may be incapable of generating enough pressure due to some internal 
failure.  Another possibility is that the free-fall valve is open or has 
failed.

I'm afraid the only sure answer I see is to measure the pressure some other 
way (with a gauge) and see what happens.  If the pressure comes up but the 
system doesn't shut off, and the "forced switch closure" trick above makes it 
shut off, then you have a bad switch.  If the pressure doesn't come up, the 
problem is not electrical.

Maybe someone else, after their morning coffee, can come up with other ideas.

- Rob Wolf

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