Internal Vibrator:

Internal vibrator is also known as needle or immersion or poker vibrator. It consists of a power unit and a long flexible tube at the end of which fitted a vibrating head. These vibrators have higher effectiveness since all the energy is directly transmitted to the concrete. As they are portable, therefore, can be readily used in difficult positions. The vibrating element is immersed in the fresh concrete, that transmits vibrations through the vibrator body. It is very important to keep the vibrating head in the concrete while running in order to keep the bearings cool and avoid breakdowns. It should be inserted vertically or nearly so at points 45 cm to 75 cm apart and should be withdrawn slowly at the rate of 7.5 cm/sec. These should not be used for pushing concrete laterally in the formworks because it will cause segregation. The frequency of vibration is about 7000 cycles/mt. Such vibrators are used for compacting large sections of mass concrete in structures, for concrete of beams, columns, foundations, etc.

Figure: Internal Vibrator