A) heavy coil springs is the correct answer. The safety heads of most large reciprocating compressors used in refrigeration systems are held in place by heavy coil springs. This is a common safety design feature to ensure the safety head can quickly and reliably open in the event of an overpressure condition, allowing the pressure to be safely relieved. The other answer choices are incorrect. Teflon gaskets would not provide the necessary strength and reliability to hold the safety head in place. Tack welding would make the safety head difficult to replace or service. Discharge pressure in the relief valve return line does not directly hold the safety head in place.