Viair 450?

I know some of you dont liek them, but whats the longest you've left it running? I can't get mine up to 175 psi without feeling hot as hell. I dont wanna burn up my compressor, but I need more air on a regualr basis. I only have one and am getting a second. so maybe that will help. Also, can I run 2 comps with one relay or do I need 2 seperate realys? or do i even need one at all?