The surge tank is one of the most important things in a facility or any place that needs water control. It is used as a large reservoir or a pipe which is placed in a vertical position to extend the water supply. It is mainly useful when small pipes are connected to the mains so as the pressure of the water builds up, the surge tank reduces it. This is the simple definition of the Surge tank.
We can often see surge tanks in medium or large plants.
Now getting into the details on where we use it, how we use it and why we need it.
If you have any basic ideas about how we generate hydroelectric power you might know what I am about to say. In simple term, I would consider it as a gift for us.
Where is Tank Placed and How Does It Help
This tank is installed on large pipelines so that when the pressure is exceeded due to the water hammer it can stop it and also supplies water when there is a negative pressure in the pipelines when the valve opens. A simple tank placed vertically above ground and made of concrete is capable of things we can’t imagine.
We can see surge tanks in dams. Some time’s this dams has excess water running through them and sometimes it has very less. This is when surge tanks stand up, and yes it has to be placed as close as possible to the power plant. As the demand or load increases the surge tank release water to move in and when the demand or load is too low the surge tank will absorb the water back into the tank.
This is how a surge tank reduces any change in pressure due to the speed of the water. In the next lines, you will see how to control various pressure and using what, before that, I would want you to see a simple thing of what causes the water hammer inside the surge tank.
Another name for surge tank is hydraulic shock and the reason behind this shock is when water suddenly changes its course or just stops out of nowhere is the reason for the hydraulic shock. The sounds you hear around a dam or anything that has water flowing through at great velocity through pipe sometimes give some sounds like banging this is due to the shock wave.
Types of Surge Tanks
There are many types of surge tanks and all have almost the same function but works differently:
1) Gallery type surge tanks: This is two chambers that are placed above and below a surge tank. They help the surge tanks In the same way but in a different method, like for instance when the load decreases the lower chamber below the surge tank will release water to maintain the load and when the pressure or load rises the above chamber would absorb it and bring the pressure to a minimum.
2) Restricted orifice surge tanks: Restricted orifice consists of an orifice plate which is a device used for measuring flow rate for reducing pressure or for restricting the flow of water. It consists of a throttle that controls the rate of flow inside the pipe. The advantage of this orifice is when there is excess load the narrow space due to the orifice will reduce friction and the excess pressure in the pipe will be removed. And for this pressure to be removed the orifice has to be designed perfectly as any fault in the design could lead to disaster.
3) Differential surge tanks: This surge tank has an internal riser that is placed in the tank permanently. This riser has a very small diameter through which water enters into the riser when it overflows. The riser also comes with an annular port at its end. And this port helps to control the flow of water into and out of the surge tank.
4) Simple surge tanks: This tank can be used for simple low heads that don’t need much precise and accurate design like the other tanks. But if you keep then under long heads we must bring modification or change to this tank.
Surge tanks are really big, this is to prevent water from flowing out so it has a very large height. But we can sometimes let water to overflow through the tank without getting it damaged.
Safety Precaution for Surge Tank
The must thing you should do when you build a surge tank is to keep the bottom of the surge tank full of water. This is because it will prevent air from entering inside. This air might not seem to be a problem at first but gradually as the air would rise it would damage the drain lines. when a faucet is turned on and then quickly turned off, this forces the water to move backward. Excess water pressure in the system of the plumbing can cause damage to a home's water line. All this variable pressure created in the long pipes are controlled by a simple surge plantation which is placed close to the turbines. Surge tanks that are visible or above ground are usually made of steel or concretes. The amount of water that can be stored inside the surge tank is known as surge capacity of the tank.