Hydrant Pumps

Introduction

What are Hydrant Pumps?

          It is a machine which raises water from a lower level to a higher level and from one place to another by the action of centrifugal force.

Centrifugal force      

    It is that force which acts upon a body moving in a circular path, tending to force it farther away from the center of the circle in which it is moving.

1.    Working Principle

          When the rotating member of the pump which is called “Impeller”, gives fast rotary motion to the mass of liquid contained in the casing surrounding it, the centrifugal force forces it out of the casing through the discharge outlet. The vacuum thus created makes atmospheric pressure to push in more water into the casing through the center, called the “eye” of the impeller.

2.    Construction

          The pump has two main components:

1. Impeller

2. Casing

Impeller

:     It is the only moving part in the pump. The vanes of the impeller extend from the center of rotation to the periphery. These vanes are closed by means of two discs, one on each side. These discs are called shrouds. The vanes are curved slightly forward. It has a round opening in the center which is called ‘eye’ of the impeller. The main function of the impeller is to provide high velocity to the mass of water entering through its “eye”.

Casing:       The casing is the enclosure in which impeller rotates. This is do designed as to reduce the turbulence created by the water as it is discharged in the volute which steadily increases in diameter till it reaches the delivery outlet.

          The main function of the casing is to convert velocity energy into pressure energy. The high-pressure liquid in the volute recalculated behind the shroud of the impellor causing an end thrust tending to force the impellor off the shaft. A thrust ball bearing is installed to counteract this force.

Motor:         The pump is connected to a motor by means of a shaft with the help of a coupling joint. To prevent leakage of water a mechanical seal is provided between the casing and the shaft. It is also done by providing a packing of fire-resistant material such as asbestos called “gland packing”. A small leakage is retained in this case of prevent its damage by the frictional heat.

3.    Characteristics

1. At any given speed, when there is no flow the discharge pressure is at the maximum.

2. The pressure decreases progressively with an increase in the discharge rate.

3. Both pressure and flow increase with the increase in speed and vice versa.

4. The power absorbed by the machine increases as the flow increases and vice versa.

5. Keeping the revolutions per minute constant the discharge low rate falls as the suction lift increases.

4.    Installation

         Centrifugal Pump commonly called “Fire Pump” is installed:

        1. To cater fixed Fire Hydrant System.

        2. On the Fire Engine (movable).

5.    Water Supply

· The pump takes suction from water reservoirs constructed overhead (Positive head) from underground (Negative head) or static reservoirs.

· When connected from positive head source the pump is provided with isolation valve called “Suction Valve”.

· When connected from Negative head source the suction is provided with a foot valve.

· All pumps have an isolation valve in the discharge side called “Discharge Valve”.

· All pumps are provided with priming facility designed suitably for different applications.