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What is a Surge Tank?
A surge tank is a water storage device used as a pressure neutralizer in a hydropower water conveyance system to resists excess pressure rise and pressure drop conditions.
Functions of Surge Tanks
The important functions of surge tank are as follows
- It should Protects the conduit system from high internal pressures.
- It should help the hydraulic turbine regarding its regulation characteristics.
- It should store the water to raise the pressure in pressure drop conditions.
Location of Surge Tanks
The location of surge tank is also important to produce better results. It should be located in such a way that
- Surge tanks are located near to the power house to reduce length of penstocks.
- No limitations regarding surge tank height.
- Location at which flat sloped conduit and steep sloped penstock meets.
Types of Surge Tanks
Various types of surge tanks used in the hydropower water conveyance system are as follows.
- Simple surge tank
- Gallery type surge tank
- Inclined surge tank
- The restricted orifice surge tank
- Differential surge tank
Simple Surge Tank
A simple surge tank is like vertical pipe which is connected in between penstock and turbine generator. These are constructed with greater height and supports are also provided to hold the tank. Whenever the water flow suddenly increased the water is collected in the surge tank and neutralize the pressure.
Top of the surge tank is opened to atmosphere If surge tank is filled completely then it overflows to maintain the pressure neutralization.
Gallery Type Surge Tank
Gallery type surge tank consists of extra storage galleries in it. These storage galleries are also called as expansion chambers. So, gallery-type surge tanks can also be called expansion chamber-type surge tanks.
These expansion chambers are generally provided below and above the surge levels. Below surge level chambers are used to store excess water in them and released when it is required or there is a brief drop in pressure. Upper surge level chambers are used to absorb the excess pressure.
Inclined Surge Tank
In the case of an inclined surge tank, the surge tank is provided with some inclination. It is provided when there is a limit in height of the tank. By providing an inclined surge tank the overflowed water under excess pressure is entered into the inclined tank and pressure destroyed.
Restricted Orifice Surge Tank
Restricted orifice consists an orifice between pipeline and surge tank. This orifice is also called as throttle so, it is also called as throttled surge tank. This throttle or orifice have very small diameter.
If the water overflows it should enter into the surge tank through this orifice. Because of small diameter frictional losses will developed and excess pressure in main pipe line is destroyed. This will creates quickly a retarding or accelerating head in the conduit. To reduce the water hammer effect, diameter of orifice should be well designed for full rejection of load by the turbine.
Differential Surge Tank
In case of differential surge tank, an internal riser is fixed in the tank. This riser have very small diameter through which water enters into the riser when it overflows. The riser also contains annular ports at its lower end.
These ports help the flow into or out of the tank. So, the excess pressure is destroyed by the internal riser of the surge tank and storage of water is done by the outer tank. So, it is called a differential surge tank.