Inverted traps.

[NotThatBright]

If your condenser is located below your evaporator is there any point to an inverted P trap at the top of the riser in the suction line? Working on some coolers/freezers and the installation manual calls for suction line traps every 15ft in the riser (which I understand) and an inverted trap at the top of the walk in box and I just didn't quite understand why.

[supers_5]

Traps are only for rises, not drops. Both inverted and regular.

[ehsx]

I only use inverted traps if more than one riser to a common header or at condenser gas connection. Insure horizontal line slope in direction of flow and inverted trap is not necessary with a single riser.

[pecmsg]

Evaporator below the condensing unit gets a trap at the bottom and a inverted trap at the top.

Download
DuPonts best piping practices.

[ehsx]

Evaporator below the condensing unit gets a trap at the bottom and a inverted trap at the top.

Download
DuPonts best piping practices.

That's an consequential inverted trap only because a riser the height of the coil is recommended to prevent floodback/flooded starts in cases of power failure and non-pumpdown circuits.

[viceman]

Follow manufacturers recomendations

[jayguy]

There are inverted traps on liquid lines too. Not really relevant to this conversation. But there you go.

[pecmsg]

Duponts book lists several combinations

[ehsx]

Duponts book lists several combinations

DuPont’s one of the better guides. There is a lot of incomplete, conflicting & inaccurate information out there, vendor and manufacturers.

I wrote the McQuay/ Daikin requirements for chiller products and edited their piping application guide. It’s the best and most complete I’ve seen for comfort & chill water applications. Included a number of recommendations not commonly listed. Ashrae included minimum capacity tables for oil return ~ 1990 that make a big difference in reliability and proper pipe sizing. Included liquid line check/relief arrangements and restricted double risers before any other mfg’s followed suit.
Also reviewed hundreds of proposed and installed drawings & installations for McQuay/Daikin, Dunham Bush & Lennox. Very seldom would get a clear isometric drawing with all components and tie-ins.

Note differences in Trane scroll recommendations re traps and horizontal line slope. Logic based on probable short cycling. Think better to prevent short cycling.

[hvacker]

Not really a trap. The suction piping was run above the coil when the evap was higher than the compressor..
Like a trombone. The idea was if the coil flooded because of migration, the riser would contain the refrigerant
and keep the compressor from slugging.
Maybe 15-20 years ago Carrier sent a bulletin around saying it didn't do what they thought.
The systems can migrate too much refrigerant for the riser to contain it. Instead they recommended a liquid line
solenoid to open on start up. Not a pump down, that's another topic. Just a valve to stop migration.

[pecmsg]

Not really a trap. The suction piping was run above the coil when the evap was higher than the compressor..
Like a trombone. The idea was if the coil flooded because of migration, the riser would contain the refrigerant
and keep the compressor from slugging.
Maybe 15-20 years ago Carrier sent a bulletin around saying it didn't do what they thought.
The systems can migrate too much refrigerant for the riser to contain it. Instead they recommended a liquid line
solenoid to open on start up. Not a pump down, that's another topic. Just a valve to stop migration.

OP's talking Cooler Freezers, not comfort cooling.

[Smilin Steve]

No; not for down flow suction. All it would do would be to increase the pressure drop by three 90's worth.

If your condenser is located below your evaporator is there any point to an inverted P trap at the top of the riser in the suction line? Working on some coolers/freezers and the installation manual calls for suction line traps every 15ft in the riser (which I understand) and an inverted trap at the top of the walk in box and I just didn't quite understand why.

[hvacker]

OP's talking Cooler Freezers, not comfort cooling.

Same function. His manual called for an inverted trap where some call it a riser & return. Same idea of not slugging.
Technically it's not a trap because it doesn't trap.
A solenoid does the same function but is more fail safe as the riser might not prevent slugging.