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fridge doctor
25-02-2010, 06:20 AM
Hi,

I have installed a couple of 24,000Btu cassettes. They are MAYOKI but I don't think that is important. They have a lift pump of course, and the drain outlet is 32mm. Supplied with it is a short length of 32mm flexi, which I am expected to install forming a 'rise' of not more than 400mm. The thing is if I continue the drain in 32mm pipe (and it does have to rise to about 400mm before exiting the building) then surely for it to work, the pump would have to fill up the entire volume of the 32mm drain pipe over it's whole length, and then be unable to push this huge head of water along? There is no mention of stepping down the drain pipe size. What would you do?

hyperion
25-02-2010, 08:46 AM
The 400mm lift should be as close to the cassette as possible. It is best to reduce the lift to 20/22mm pipe, otherwise the amount of water that has to be lifted is quite considerable. Also, during the off cycle, the water contained within the lift section will drain back into the cassette and could cause the high water level alarm to activate or worse still leak out of the driptray.

VRVIII
25-02-2010, 05:23 PM
Hi,

I have installed a couple of 24,000Btu cassettes. They are MAYOKI but I don't think that is important. They have a lift pump of course, and the drain outlet is 32mm. Supplied with it is a short length of 32mm flexi, which I am expected to install forming a 'rise' of not more than 400mm. The thing is if I continue the drain in 32mm pipe (and it does have to rise to about 400mm before exiting the building) then surely for it to work, the pump would have to fill up the entire volume of the 32mm drain pipe over it's whole length, and then be unable to push this huge head of water along? There is no mention of stepping down the drain pipe size. What would you do?
Hi,
Most manufactures specify the correct pipe size to be used and max lift height in the installation manual. As Hyperion said the pipe should go vertical directly after the unit outlet to the max lift height then run horizontally with a slope of at least 1:100.
The pump is not designed to push water along and then up or up then along.
If you upsize the vertical pipe section the lift height must be reduced accordingly i.e. if pipe size is doubled lift height must be halved.

fridge doctor
26-02-2010, 01:10 PM
Thanks, that makes more sense. I am going to reduce the 32mm down to 16mm for the vertical rise, and then step it back up to the 32mm on the horizontal to exit the room (the 32mm pipe is already insulated and in place). Sound OK?

eggs
26-02-2010, 02:06 PM
Did you know?.....and not a lot of people know this.. (in my best Michael Caine impression :D)

The reason for the lift limit on internal drain pumps is not anything to do with the motor performance or limitations of the pump itself.

It is to do with the capacity of the drain pan, and not soaking punters when the A/C goes dodgy.

For example suppose a 400mm lift limit on 32mm pipe = about a third of a litre. This is less than the condensate tray will hold.

Todays fascinating factoid..

Eggs