Hi Angier...... All,

The best suppression protection for the hydraulic motor solenoids is a 1N5400 series silicone diode. Any from the series 5400 through 5408 are fine. The striped end of the diodes should go to the motor leads and the plain end to the third ground lead near the motor. They are good for a 200 amp surge which gives plenty of margin for the less than 35 amp or so pump motor. The diodes prevent the voltage  across the relay contacts from exceeding main buss voltage plus a volt or so. Any accidental over voltage the aircraft might suffer will not harm the diodes unlike a zener/surge diode type solution. The energy suppressed is contained in the motor rather than in an external surge diode providing best reliability.

The solenoids provided by Lancair are very robust and I see no reason not to use them. I would include a 1N4001 series diode across the relay coil to protect the pressure switches. The solenoids can also be purchased from any auto parts store. Make sure to get the continuous duty solenoids rather than the starter solenoids. I have no beef with electronic relays except for the experimental and unproven nature of such one off solutions.

Jack Morgan