Can water hammer be prevented by installing a check valve?

A check valve is a valve that allows fluid to flow in a fixed direction and automatically prevents it from flowing in the opposite direction (reverse flow). Check valves have a wide range of applications, and in this article we will focus on check valves installed on the outlet side of steam traps.

We often ask, what is the purpose of installing a check valve? So the topics discussed in this article include:

① Is it necessary to install a check valve on the outlet side of the steam trap?

② Can water hammer be prevented by installing a check valve?

③ Restrictions on the use of check valves.

Is it necessary to install a check valve on the outlet side of a steam trap?

If there is a possibility of condensate flowing back, it is necessary to install a check valve.
For example, when condensate is discharged to a common collection line, the condensate discharged by other traps may flow back to the equipment, so a check valve must be installed under this condition. It is very important to prevent this kind of backflow, because it will not only affect the heating efficiency, but also very likely damage the trap. On the contrary, if the trap outlet is connected to a separate drain pipe for downward discharge, backflow will not occur, and there is no need to install a check valve.

Single dedicated pipeline

If the trap discharges downward to the atmosphere through a separate drain pipe, there is usually no risk of backflow and a check valve does not need to be installed.

Note: Based on the pipeline configuration behind the trap, if the equipment is in vacuum condition or the pipeline is lifted, the back pressure may exceed the primary pressure and backflow may occur. In this case, installing a check valve can effectively prevent backflow.

Common water collection lines:

If the outlet of the trap is recycled to the same condensate collection line, and if a check valve is not installed, the condensate discharged from the operating equipment may flow back to other out-of-service equipment.

If a check valve is installed, even if the outlet of the trap is connected to the same water collection line, the condensed water discharged from the operating equipment will not flow back to other out-of-service equipment.

Can installing a check valve prevent water hammer?

There are many factors that cause water hammer. The biggest cause of water hammer in the condensate recovery line is the backflow of condensate from the riser. Installing check valves in these locations can be of great help in preventing water hammer caused by backflow.

One of the causes of water hammer is the backflow caused by the riser in the recovery pipeline.

If the discharge of condensate is controlled by an intermittently operating pump and there is a horizontal pipeline in front of the riser, then the condensate flowing back from the riser may collide with the newly discharged condensate, causing water hammer. Similarly, when PowerTrap® discharges high-temperature condensate, the generated flash steam and backflow colliding with the condensate are another possibility for water hammer.

Under such working conditions, installing a check valve at a suitable location in the system (such as the starting position of the riser) can be of great help in preventing water hammer.

In the condensate delivery pipeline, the water hammer caused by the pulse flow of low-temperature condensate can also be solved by using a check valve.

Restrictions on the use of check valves:

① When the high-temperature and high-pressure condensate is discharged to a lower pressure area through the trap, a certain amount of flash steam will be generated. If the flash steam flows into the recovery pipeline filled with low-temperature condensate, the flash steam will transfer its latent heat to The condensed water condenses rapidly, causing water hammer. Under such working conditions, installing a check valve will not be effective.

② The check valve can prevent backflow but cannot reduce back pressure. It cannot allow condensate to drain from low pressure areas to high pressure lines. Even if the stop valve is installed after the trap, if the primary pressure is less than the secondary pressure, the condensed water cannot be discharged.

In addition, it should be noted that if a check valve is installed after a trap with a very small pressure difference, the check valve itself will also become a resistance point (that is, the check valve also has a pressure loss), so it is necessary to calculate the pressure drop pay attention.