Pranayama occupies the second place in “Hathayoga”, while it constitutes the fourth step of Patanjali’s ‘Ashtagayoga’.
Start practising pranayama when you become well-versed with asanas that is when a stage of asanjaya (sidha) is achieved so that one can sit for hours together, steadily and comfortably.
‘Prana’ means –a suitable life force, which provides energy to different organs (including mind) and also controls many vital life processes (circulation, respiration, etc.)

‘Ayama’ – signifies the voluntary efforts to control and direct this prana.

This is the only pranic activity available to us, which can be regulated voluntary and the breathing system is linked with nervous system and mind too. Yoga has taken best advantages of this situation, considering that the mind could be controlled effectively-with the voluntary regulation over breathing.

Pranayama means a voluntary and temporary pause in the movement of the breath so breath is a door between our physical existence and the spiritual path.

tismanasait Svaasap`Svaasayaaoga-itivacCod : p`aNaayaama:

(Tasminsati Shvasaprashvasayor gativichchedah Pranayamah)

-Patanjali Yoga sutras 2.49

The meaning is that the pause is brought in the movement of inhalation and exhalation, is nothing but Pranayama.

calao vaato calaM ica yaaogaI sqaanaU%vamaaPnaaoit ttao vaayau inaraoQayaot ÈÈ

(Chale vate chalam chittam nishchale nishchalam bhavet yogi sthanutvamapnoti tato vayum nirodhayet.)

-Hathapradipika 2. 2

So long as breathing is continued and air is moving in and out of the body, the mind remains unstable. When the breath is stopped, the activity of the mind is also controlled and it becomes standstill. Thus a yogi attains a complete motionless state of chitta (consciousness). One should therefore restrain one’s breath.

Pranayama aims primarily at the control on mind when it is at a standstill, no thought process or emotional disturbance is possible. Thus, by controlling the mind we would be able to control different emotions and as a result, the temperament, moods desire and natural instincts of mind (vrittis) would also be controlled automatically. During pranayama the breathing is consciously made slowly, deeply and rhythmically. This brings about noticeable relaxation, tranquility, balance and a sense of well being to the mind.
With regular practice of Pranayama, one can get some benefits such as the increment of capacity of lungs, good resistance power, better steadiness of mind and concentration power.

In Pranayama the duration of Kumbhaka will be as per the selected /decided time ratio that is 1:2:2 or 1:4:2.

Another important thing is that the duration of Rechaka (exhalation) will two times more than the Puraka (inhalation).