use of inverted P traps

[coldseeker2012]

Good evening to everyone. I´m quite familiar with the use and purpose of oil traps at the bottom of suction line risers, and every other 5 meters, as you go up the riser. What I didn´t know was that an inverted P trap has to be installed at the TOP of the riser as well. I just saw pictures of this in a website that describes the correct installation of walk-ins. What would be the purpose of this inverted P trap? Keeping the oil and liquid refrigerant from flowing back into the evaporator by falling through the riser when the system is off?

[Tesla]

Hi coldseeker
In short yes, it stops oil draining back in the off cycle or reduced loading. Inverted P Traps are also used on some cooling towers to stop all the water in the pipe draining each time the pump shuts down.

[Rob White]

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Yep.

As stated by Tesla the trap on the top of the riser
stops the oil from falling back down once it has reached
the top.

Regards

Rob.

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[coldseeker2012]

Good evening to all. I would like to add something I just learned in another forum: inverted P traps should be used at the top of individual suction risers whenever each riser belongs to evaporators which are being connected to a header or main suction line. In this way the oil going through the header does not fall into any of the evaporators during the off cycle. Actually, when I started this post, I was thinking on a single evaporator with a single suction riser. Thank you for your comments.

[Rob White]

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Suction pipes should always go into the top of the header
and liquid pipes should always be conected to the bottom
of the header.

Regards

Rob

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