compressor valve

Hello , I have 2 compressors 1 is a standard 3 gallon oiless setup great little system but very loud. The second setup is a tankles diaphragm compressor that is made for airbrushing. I have a moisture and air regulator on both sysrems but the small tankless does not have a auto shut off, I drilled a small hole in female coupler as to not burn out the motor but found I can only produce 15psi . I have used a toothpick to help with air pressure and does help but falls out to easily. Is there a valve or valve screw that would work for this application. Thanks Rory