Email this pageCheck Valve Installation and Benefits
Is it always necessary to install a check valve downstream of a steam trap?
A check valve is a type of valve that allows fluids to flow in a downstream direction but closes automatically to block any fluid that tries to flow back upstream (backflow). Check valves are used in a wide variety of locations, but the focus of the discussion in this tutorial will be the installation of check valves at the steam trap outlet side. We are often asked about the necessity of installing a check valve at the steam trap outlet.
- Is it always necessary to install a check valve downstream of a steam trap?
- Does installation of a check valve prevent water hammer?
Let’s discuss these questions.
When a trap outlet leads to a condensate collection line, there is the danger of backflow from the condensate discharged from other traps, so as a rule a check valve must be installed. In contrast, when there is a single downward sloping pipe that is not submerged at any point, there is no possibility of backflow, so a check valve is not necessary.
Single Pipe
If the trap outlet piping is connected to a single line that releases to atmosphere without being submerged at any point, there is no need to install a check valve.
Trap Outlet Collection Line
If the trap outlet piping is connected to a condensate collection line, condensate discharged from equipment in operation will backflow into equipment that is out of service unless there is a check valve installed.
If a check valve is installed, even if the trap outlet piping is connected to a collection line, the condensate discharged from equipment in operation will not backflow into equipment that is out of service.
Does installation of a check valve prevent water hammer?
There are various mechanisms that generate water hammer, but a main cause of water hammer in vertical rises in condensate recovery lines is condensate falling back down. The installation of a check valve at each of these locations is very effective in preventing water hammer. Condensation-induced water hammer occurs frequently in condensate return lines, but backflow plays no role in this type of water hammer so the installation of a check valve is not effective in this case.
Additionally, although this has no direct connection to water hammer, it is a matter of course that just because a check valve has been installed does not mean that it is acceptable practice to connect low pressure condensate to discharge into a higher pressure condensate recovery line. Furthermore, if a check valve is installed at the outlet of a trap operating under an extremely small operating differential pressure, the check valve itself becomes a point of resistance, which means that it is necessary to calculate pressure drop very carefully.
Condensation-induced Water hammer
When high pressure hot condensate flows into a collection line that contains low pressure cold condensate, flash steam is generated. If this flash steam then rapidly condenses, water hammer may result. Installation of a check valve is not effective against this type of water hammer.
Water hammer caused by condensate falling in vertical rises in condensate recovery lines
If the condensate discharge piping on a pump with intermittent operation (e.g. PowerTrap series, motorized pump with ON-OFF by a tank) has a long horizontal run followed by a vertical rise, any condensate that falls back down the vertical rise becomes a backflow that crashes into the condensate newly discharged by the pump, resulting in water hammer.
This type of water hammer can be prevented by the installation of a check valve at each critical location (e.g. the beginning of a vertical rise).
Additional information: Incorrect Piping
Even if check valves are installed, it is not possible to discharge low pressure condensate into a higher pressure line.
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