The correct answer is B) heavy coil springs. The safety heads of most large reciprocating compressors used in refrigeration systems are held in place by heavy coil springs. This design allows the safety head to quickly and reliably open in the event of excessive discharge pressure, providing a critical safety mechanism to prevent catastrophic failure of the compressor. The other answer choices are incorrect because: A) tack welding would not allow the safety head to properly function and open, C) the discharge pressure in the relief valve return line does not directly hold the safety head in place, and D) large Teflon gaskets would not provide the necessary structural support to withstand the forces involved.