LOW PRESSURE

Hi I have an Ingersoll Rand ssr ep 7.5 with 18000 hours on it.The pressure it builds wont go over 80psi. The intake air filter is new, the ultra coolant level is good but I noticed the coolant foams when compressor runs (not sure if this is normal).I cant hear any other leaks. Any suggestion why not enough pressure buildup ? Thanks for your help. CJ SINGH, YUCAIPA, CA