Surge tanks are used to control pressure change in the system due to changes in the water flow rate. In a small pipe system and even a large pipe system by controlling water flowrate we can control this problem and only some water hammering noise will come.
But, in the turbine system (Hydroelectricity production unit) we cannot control the water hammering problem by simply controlling the water flowrate we need to provide a dedicated solution to this problem.
The solution to this problem is nothing but the surge tank.
The Surge tank will provide extra water when demand is very high and will suck water when demand is very low this is the basic understanding of the surge tank.
How does Surge Tank work?
The full turbine system is shown in the figure. Water is stored in the reservoir mostly Dam. Then it flows through the pipe and via pen stock goes to the turbine section. The surge tank is located in between this pipeline.
It should be near the power plant. As shown in figure surge tank should be mounted below the reservoir water level to ensure no air in the pipeline. Also, it will keep the surge tank full of water. The surge tank should be large enough so that it won’t overflow.
When the demand for water increases at that time pressure at the valve will increase and cause water hammering sometimes causes pipe failure.
To eliminate this surge tank will provide excess water which will control excessive pressure. When exactly the opposite situation occurs negative pressure will appear and to compensate that surge tank will store extra water in it and maintains normal pressure.
The surge tank controls the shock of water so it is also called the Hydraulic shock.
Surge Tank Types
- Simple Surge Tank
- Restricted orifice surge tanks
- Differential surge tank
- Gallery type surge tank
- Simple Surge Tank
1. Simple Surge Tank
Simple Surge Tank is used when we don’t need preciously designed surge tanks. In this type, a vertical pipe is connected between the turbine and penstock.
When water pressure increases it will neutralize it. The tank is open to the atmosphere when the head increases water is directly thrown outside.
2. Restricted orifice surge tanks
Restricted orifice surge tanks are very useful because it reduces pressure in a short time compared to the simple surge tank. It is also connected to the pipe near the turbine.
It contains an orifice or throttle at the bottom of the tank which will cause very high friction for excessive water and which produces very high head. Due to this pressure reduction will take place very rapidly.
3. Differential surge tank
Differential surge tank is a combination of both simple and restricted surge tank. It contains one riser of a small diameter.
When water overflows it will pass through the raiser and go to the surge tank. It also contains an annular port at the bottom to control water flow.
4. Gallery type surge tank
Gallery type surge tank contains two tanks that activate based on the situation. When pressure increases water will be absorbed in the upper tank.
When the water level reduces the lower tank will provide extra water.