A monoblock gas compressor for use in compressing gas having a supply pressure greater than the atmospheric pressure is provided. The compressor includes a compressor head mounted to a cylinder block such that a plurality of valve receiving bores formed in the cylinder head are aligned with a bank of cylinders of the cylinder block. A compressor valve is disposed in the valve receiving bores and secured therein with a valve retainer. The valve retainer defines a gas inflow path to the compressor valve and a gas discharge path away from the compressor valve. The compressor head has a plurality of gas inlets extending from a side of the compressor head and intersecting a corresponding one of the gas inflow paths, thereby enabling the compressor head to safely receive supply gas at a pressure substantially greater than atmospheric pressure.