How much air pressure to change springs?

How much air is needed in the cylinder to change valve spring?
What is the smallest compressor you can use to complete this job?

i've heard 50 or 60 pounds.

i did mine by just using the TDC method. that way the valves can't drop into the cylinder. they drop about an inch and hit the top of the piston.

worked great. just took alot of double checking to make sure i was actually AT tdc on the proper cylinder ;)

ttt