The air tank will rust and eventually leak air if you don't drain condensate water from the tank through the tank drain valve regularly. Replace the air tank if you see rust on the bottom of the air tank. Loose air tube fittings will allow air to leak out of the tank, so tighten all air tube fittings to prevent air tank leaks. A failed check valve will allow tank air to escape through the unloader when the pump stops running. Replace the air compressor check valve if air leaks out the unloader when the pump motor stops. A leaky safety valve or leaky drain valve can also allow tank air to escape. Replace the leaky safety valve or drain valve.
These repairs may help solve your air compressor problem
Replace the air compressor check valve
The check valve prevents tank air from back flowing to the pump. A failed check valve will apply high air pressure to the head of the pump preventing the motor from restarting once the tank has filled. If the motor starts when the tank is empty of air but won't restart when the tank is full, replace the check valve.
If your air compressor won't restart after the tank fills, the check valve might be the problem. This DIY repair guide and video explain how to replace an air compressor check valve in less than 15 minutes.
If your air compressor's gauges show that the tank isn't building pressure, the pump might be the problem. This DIY repair guide and video show how to rebuild an air compressor pump with step-by-step instructions.
The safety valve pops open to relieve excessive air pressure if the pressure switch fails to shut off the air compressor at the cut-out pressure setting. Replace the safety valve if it leaks or pops open at normal operating pressure.
Replace the air compressor tank
Don't try to fix a leaking air compressor tank. Replace the tank if it leaks air.