What is air trapped in piping? Piping points to prevent air from getting in
Some people may have had trouble resolving the issue after air got trapped in the pump piping.
To prevent air entrapment, it is effective to devise piping methods to prevent air from getting mixed in before the problem occurs.
This time, we will introduce the causes of air entrapment and effective piping methods to prevent air entrapment.
1. What is air trapped in piping?
Air entrapment is a phenomenon in which air gets mixed in while the pump is running, or gas dissolved in the fluid separates, causing bubbles or air pockets, preventing the expected discharge pressure and flow rate from being achieved.
Centrifugal pumps, among other pumps, cannot pump out gas, so if air gets in, the pump will run idly and the discharge pressure will drop suddenly. In the worst case scenario, the piping and the pump may be damaged.
There are many possible causes of air entrapment, but they can be broadly classified into the following three categories:
- ・Air is easily generated or mixed into the pump.
- ・The pressure in the filter tank has increased, making it difficult to remove the trapped air.
- ・The pump is installed in an inappropriate state or in an inappropriate location.
There are many possible causes for air entrapment, so if air entrapment occurs, you have to check each check point one by one and repair it, which takes time. For this reason, it is important to devise a piping method that prevents air from getting in in the first place.
In the next chapter, we will look at piping methods that are less likely to cause air entrapment.
2. Pay attention to the suction side piping
First, we will introduce the piping method on the suction side. The suction side is the most susceptible to the effects of air entrapment, but because it is basically a negative pressure, there are restrictions such as not being able to use an air bleed valve.
Pay attention to the following piping methods to prevent air from getting into the piping.
■ No Torii piping
Due to the installation location, there are cases where the piping is raised and then lowered in a convex shape, which is called Torii piping.
When installing Torii piping, air, which is lighter than water, will accumulate in the convex parts, creating air pockets.
Although some air can be removed by flowing the fluid forcefully, it is difficult to remove all of the air, so Torii piping should be avoided.
■ Do not install piping with a downward slope
Downward sloping piping, where the slope of the piping decreases towards the pump, should also be avoided as this may result in poor suction due to air pockets.
The principle behind air accumulation is the same as that of Torii piping, where air rises and accumulates at the top of the piping.
To remove the air, the pipe needs to be sloped towards the pump. As a guideline, the pipe should have an upward slope of 1/100 or more.
*1/100 gradient: 1cm drop per 1m
However, when installing a pump at a position lower than the liquid level in the tank using forced piping, care must be taken because the piping must be laid at a downward slope toward the pump so that air can escape into the tank.
■ Ingenuity in the installation method of the foot valve
If the pump is installed above the liquid level in the tank, a foot valve may be used to prevent backflow of the fluid. If the foot valve is not installed correctly, the valve may not close properly, allowing air to enter.
Make sure to install the foot valve in the correct direction after carefully inspections its operation. It is also important to install it in a location that is easy to access for maintenance so that any incorrect installation can be corrected immediately.
■ Prevents air from entering through the connection
Although air can easily get in through pipe connections, it is also a place where it is very difficult to detect air intrusion.
Generally, flange connections, which are less likely to leak, are considered to be the best way to prevent air from getting in. If you use threaded piping instead of flange connections, be sure to thread and tighten properly to ensure a tight seal.
3. Important points when connecting valves and pipes with different diameters
Even when connecting valves or pipes with different diameters, air can easily get in if you do not follow the precautions. Let's check the points to keep in mind when making each connection.
■ Install the valve horizontally
Due to their structure, valves such as gate valves are prone to air accumulation.
It is best to place the valve handle lying flat on its side to prevent air from accumulating in the handle.
■ Use eccentric pipes for pipes with different diameters
When connecting pipes of different diameters, air tends to accumulate at the top of the pipe, making it more likely to become trapped.
When connecting to pipes of different diameters, use an eccentric pipe to keep the top level.
4. Use an air release valve on the discharge side
Unlike the suction side, an air vent valve can be used on the discharge side piping of a pump. An air vent valve is a component used to remove air from the piping, and when air flows in, the float that was in close contact with the valve body drops, allowing the air to be expelled.
If you have no choice but to install Torii piping or if you want to remove air from a sealed container (such as a tank or filter), you can install an automatic air release valve to remove the air.
When installing, place it at the highest point, such as the very top of the torii piping or the top of the airtight container.
５．まとめ
Air gets mixed in while the pump is running, causing a drop in discharge pressure and flow rate, which can lead to piping damage, so it is important to devise a way to install the piping to prevent air from entering in advance.
Air entrapment can be reduced by avoiding piping methods such as Torii piping, paying attention to how valves are installed, and using seals and eccentric pipes when connecting pipes.
Once air has accumulated, it is difficult to repair, so be sure to pay attention to the points to prevent air from getting into the piping.
