Once compressor reaches 125 lbs. pressure, the

Generally, the safety/relief is set to 140 to 160psi. The pressure setting is stamped on the side of the valve. Replace the valve if it will not hold stamped pressure(cost about $6 at Lowes Lumber).The pressure switch is usually set at the factory to 120 - 130 psi. The unloader part of the pressure switch will not release backpressure unless it reaches set cut-off. The 1/4 inch line attached to the pressure switch connects to air discharge tube at the intank checkvalve (brass valve). The safety valve should very rarely release pressure, only when pressure switch malfunctions and allows pressure to reach up to 160psi. The tank will hold over 300psi so dont worry about the 160psi safety. I am not sure about your exact model number or brand, however most small compressors work the same and share similar parts. For manuals to other similar compessors to to www.dewalt.com. Here you will find manuals to dewalt and porter cable compressors. I prefer to use generic replacement parts from www.grainger.com or from Lowes Lumber. These parts will cost less than factory replacement. If you need to replace the pressure switch, use SquareD brand from grainger. Watch fitting sizes and pressure range. Good Luck on your repair.