BTW, forgot to mention one more thing: you need to create a compressor object too. The compressor power should be hooked to a Spike relay and the pressure switch should be hooked to a digital input channel.
Code:
#define PRESSURE_SWITCH_CHANNEL 1
#define RELAY_COMPRESSOR_POWER 1
private:
Compression *m_compressor;
...
// In some constructor
m_compressor = new Compressor(PRESSURE_SWITCH_CHANNEL, RELAY_COMPRESSOR_POWER);
m_compressor->Start();