The water distribution system is well designed by many mechanical systems such as valves, pumps to control and to properly distribute water and the Surge tank is one among them.

You may be aware sometimes the velocity of water will become slow when we open all taps in our home!.

At the same time the water flow will be high when we open only one tap, it happens due to the fluctuation in water pressure and it affects the water velocity. It will be really irritating but it does not make any major issue for the water flow. 

Tap Valve

At the same moment just imagine, suppose the above issue happens on a distribution system of a village or town it will cause a very serious problem. The water pressure fluctuations will damage the pipe and the valves. 

What is a Surge tank?

Surge tank is a small size of balancing reservoir, used to control the water flow velocity in a hydropower plant, water pumping system when the water comes from penstock. 


The surge tank will be located at maxim water level and near to the water source to minimise the length of the penstock & reservoir. The top portion of the surge tank may open to the sky or closed with pressurized air and it is constructed either by concrete or steel plates. 

Surge Tank
Surge Tank
  • Mostly, the top end of the surge tank may open to the sky by construction of concrete or masonry.
  • When the surge tank is constructed by steel then the pressurized air will be filled into the tank. 

Function of surge tank

The main function of a surge tank is to neutralize or control the velocity of water flow when the water suddenly rises or lowers its level from the penstock.

  • It protects the conduits during high pressure levels
  • During high water flow from penstock the tank stores the excess water to balance the pressure on conduit
  • At the same time the surge tank will release the stored water during pressure drop

How does a surge tank work?

The surge tank is a necessary part for a hydro power plant for smooth operation and control of water velocity. The surge tank is used in hydro power plant systems to secure the pipe and valves from pressure damages. 

Water Hammer – Actually, the water will flow at some velocity on the pipe. The velocity of water will be changed due to the sudden close of valves and it induces high pressure which creates water oscillation on the pipe. It develops vibration on the pipe and makes a loud noise that is called a water hammer

Water Hammer Effect
Water Hammer Effect

The water hammer can destroy the pipe and valve so the surge tank stores the water due to the rapid change of water flow. The surge tank controls the pressure changes in the pipeline and avoids the water hammer. 

  • It enhances the flow of water to the turbine by controlling the velocity of water from the penstock.
  • It reduces the distance between the turbine and free water surface which can minimise the water hammer.
  • It provides sufficient water supply to accelerate the turbine when the load is increased and also store the excess water when the load is decreased. 

Types of surge tanks

  • Simple Surge Tank
  • Restricted orifice surge tank
  • Differential surge tank
  • Inclined surge tank
  • One way Surge tank

Simple Surge Tank

A simple surge tank is located at a short distance between the penstock and turbine.  The water will be stored to the surge tank when the water flow increases and its top portion will be open to the sky which is allowed to over flow or to neutralize the water pressure. 

Simple Surge Tank
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Restricted Orifice Surge Tank

This type of surge tank consists of a minimum diameter orifice between the main pipeline and the tank. Excess water will pass through this orifice to the tank. The pressure in the main pipeline will be reduced due to the frictional losses happening by the water flow in small orifices. 

The diameter of orifice will be well designed to avoid the water hammer effect based on the maximum and minimum water flow from the penstock to the turbine.

Restricted Orifice Surge Tank
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Differential surge tank

An internal riser pipe which consists of a small orifice is fixed in the tank. The excess water can pass through this orifice and overflow to the outer tank for storage. Bottom of the riser contains a hole which is allowed to in or out the water to the tank, is called a differential surge tank.

differential surge tank

So the pressure in the main pipeline can be easily controllable by this type of surge tank. 

Inclined surge tank

The surge tank constructed with some degree of inclination is called inclined surge tank. Actually many methods have been followed to proper stream of water and avoid the water hammer effect and inclined surge tank is one among them.

The excess water coming from penstock goes into the tank and reduces the pressure in the pipeline.

Inclined Surge Tank
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One way Surge tank

The one way surge tank is like a simple surge tank system located between penstock and pumping station or turbine at maximum head. 

One way surge tank
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It can allow water flow out only & does not collect the water return from the pipeline because it does not contain non-return valve connection. A separate pipeline will be connected to the surge tank for inlet water to the tank.

Surge tank benefits

  • It can reduce the water hammer effect in the pipeline and so the valves, pipes, pumps can be secure from the damages.
  • Surge tanks collect the excess water from the penstock & whenever the water flow is reduced it can release the water for smooth distribution.

Happy Learning 🙂


Bala is a Planning Engineer & he is the author and editor of Civil Planets.

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