Frequency of the surge cycle varies inversely with the volume of the system. For example, if the piping contains a check valve located near the compressor discharge nozzle, the frequency will be correspondingly much higher than that of the system without a check valve. The frequency can be as low as a few cycles per minute up to 15 or more cycles per second. Generally, the higher the frequency, the lower the intensity. The intensity or violence of surge tends to increase with increased gas density which is directly related to higher molecular weights and pressures, and lower temperatures. Higher differential pressure generally increases the intensity.