air compresser ?

hi i undone the main pipe from compresser to air tank there is air but not full pressure as its weak once it gets to the air dryer junction plus the air gauges are not building up suffient air to release the brakes / handbrake so still at a loss lol any ideas is the gasket on the compresser a common air brake fault is it somethink i can do myself or dos it require garage repair thanks ..