lift fittings for condensate returns?

LILJohn

How exactly do these things work ? I'm having a hard time conceptualizing how they function

pecmsg

Lift fitting?

Pumpguy

In order for water to go uphill in a condensate return line through a lift fitting, there has to be a difference in pressure between the low side and the high side.

I've never seen a lift fitting in a simple gravity system, so this needs to be a vacuum return system.

Simply put, the vacuum pump pulls a vacuum on the downstream (upper) side of the lift fitting. The vacuum pressure needs to be lower than the height of the water column height of the lift.

The higher pressure in the low return line pushes the condensate through the lift fitting and up the lift pipe.

If the higher return line is more than 10' in length, the lift pipe will have a loop over where it allows the lifted condensate to drop down into the higher return line.

To keep the low return completely drained of condensate, the lift fitting has to have a loop down first so the upstream low return line can be completely drained of condensate.

At one time, cast iron lift fittings were available, but not anymore, at least as far as I know.

The attached file goes into details about lift fittings, and show how a constructed lift fitting is assembled. Kind of complicated and labor intensive I think. I don't see why a common plumbers P trap wouldn't work just as well.

And the reason the lift pipe is 1/2 the size of the return line it to increase the velocity and provide a
more reliable and constant lift.

Also, keep in mind that in order for the lift to work, there has to be a pressure differential. When the vacuum pumps turns off or stops working due to too hot condensate, the pressure differential is lost so condensate fills up the low return line and now the whole return has a water seal and can't vent.

A lift fitting should never be substituted for a proper Auxiliary Accumulator Tank with vacuum relief valve, pressure vent line with check valve, and a float switch to activate the vacuum pump.

jumper

Is what you describe also called a siphon, Dennis?

EBEBRATT-Ed

The lift fitting just collects condensate like a sink trap collects water. The riser out of the lift fitting and the pressure differential lifts the condensate. But what Dennis posted explains it all.

LILJohn

thank you dennis , it seems simple now lol

Pumpguy

jumper said:

Is what you describe also called a siphon, Dennis?

I don't think so. If I understand the siphon principle correctly, the weight of the falling column of water on the downstream side creates the pressure differential for atmospheric pressure to push (lift) water on the upstream side.

In a condensate lift application, a vacuum pump, and not a falling water column, is what creates the pressure differential.