Randy,

 

Remember that the reservoir needs a small vent hole so that air pressure or vacuum does not build up in the reservoir itself.  Usually the vent is in the filler cap or its threads.

 

With the way the hydraulic system is currently designed, you equalize the pressure on the high and low sides when it is opened. For those of us who have pressure gauges, you can see that you can have significant pressure on the system even when the valve is opened. I want to be able to not only equalize the pressure between the high and low sides of the hydraulic system with the dump valve but also release the pressure on both sides.

Today I purchased a 3 way valve to do just that. The idea  is to open the valve  connecting  the high and low sides and also releasing the pressure back to the tank.
I will most likely run a low pressure line like nylaflow back to the pump and make spin up a custom fitting on the lathe out of aluminum to go into the dipstick hole and terminate the return line there. I will make a needle dipstick checker that will screw into the same fitting for checking fluid level.
If you wanted to do it the easy way, you could always just dump the low pressure line out the belly of the airplane onto the ground. It would take very little fluid to drop the pressure and there would be no need to deal with connecting the low pressure fluid line to the tank.

I hate pulling the airplane out of a cool hanger into the warm sunshine and watching the gear pressures rise to 6-700 lbs before the master switch is turned on! We all know what happens when they hit 900. Yep no gear retraction as the upper limit has been tripped by the system pressure.
My new valve would fix that!!!
I hope...