Hi Peter –

 

I had the same problem during my initial gear testing. I originally thought air in the lines was making the fluid “springy” and allowing pressure surges in the lines to confuse the pressure switch. It turned out to be a faulty low pressure switch. The switch worked fine in the middle of its adjustment range, but when the adjustment screw was set near the top of the adjustment range, there was not enough hysteresis in the switch, and the contacts wouldn’t open cleanly.

 

I discovered this by removing power from the pump as soon as the gear were down and locked. With power still applied to the relays, I could hear a “sizzle” sound coming from the low pressure switch. This was the contacts gradually separating and arcing (they should separate quickly with a snap action). This sizzle caused the relays to clatter on and off for a few seconds. The solution in my case was to get a pressure switch with a higher adjustment range.

 

In your case, try setting the switch to the middle of its adjustment range. I needed the higher range because I close my inner gear doors after gear extension, and 550psi isn’t enough to overcome the emergency opening springs. Lancair’s pressure switched are made by Suco, Inc. http://suco.us/24pressure.html

 

Hope this helps,

Adam Molny

Legacy #151