P Traps at Evaps

[Blueboy]

Ok guys, try this one, my apprentice asked me today why do we come out of and evap into a P trap and then go through the cold room ceiling into another inverted one. With the new gases and our knowledge of refrigerant flow velocity and volume and the amazing quality of oil separators available is there any need !!!! I said liquid he said suction accumulator! Bloody apprentices I said I'd ask you guys

[Peter_1]

Why the inverted trap on the ceiling?Never did and saw this.
The linee must just have a slope towards the compressor, that's all.

P trap under the evaporator is to ensure proper oil return.
I rarely install them. If it's less then 3 ft, then we just install a smaller section upwards.

[Andy]

Hi Blueboy
on flooded applications traps are rarely fitted, oil return is either by the hot gas during defrost or thru careful selection of the pipe sizes to ensure proper velocities, 10m/sec comes to mind.
I would say with the oils we use now, POE. PAO and AB oil return traps are less important.
Better still to use traps were part load operation is envisaged, say a main suction riser on a pack or a mains suction fed by a number of rooms that of-cycle.
I suppose the old story, better safe than sorry, it's a lot easier to let the oil get there than to remove it.
Kind Regards. Andy

[Blueboy]

hmm So then to summarise!! Our considered option is as the apprentice said with new gasses and correctly sized pipe and well commissioned plant with correct components (good oil sep and suction accumulator may be) a P after the evap and certainly the one above is not required

[Andy]

Hi blueboy
maybe not required, but still good practice to fit a p trap at the evaporator. We tend to use pump-down, so little liquid is present to affect the bulb on start up.
I would say modern evaporators have nicely fabricated header which are traps in themselves. All the same I would still fit a trap.
Kind Regards. Andy.

[shogun7]

On a system where there is a direct drop to the condenser a "P" trap is not necessery, however, when the cond unit is above the evap then you should use a "P"trap for 2 reasons
1. On lite loads oil will tend to accumulate in the evap and should drain in "P" trap then as load increases mass velocity will increase in trap threby helping to facilitate oil return.
2. It helps to make sure that no liquid refrigerant is in contact with sensing bulb especially after a defrost