Horizontal Air Handler water leak

[geno]

I have a customer with 5 AH's with that are 10 ton systems each. The drain and coil are in the return side of the unit. These units get water leaks with minimal dirt in their traps. I'm getting less than 1/2 an inch static across the coil (you can see through most of it). The drain pan drain outlet is on the blower side of the coil and the trap is piped exactly to the manufacturers recommendation. The return air Grills are about 5 ft. from the units with two filter racks in them. I think the static is to high and were sucking air through the drain holding up the water from draining in a steady flow. The drain lines are 35 to 50 ft long with slifght pitches. When I put an elbo at the end of one drain line the condensate flowed at a regular rate! Any thoughts?

[Brian_UK]

It seems that you have found the answer. Althoug the pd across the coil is low it is the pressure at the drain position which counts, also allowance needs to be made for when the filters start blocking.

Increase the size/depth of the traps and the problem should disappear.

It is sometimes worth playing with some clear plastic tubing attached to the traps so that you can see what is happening when the depth of trap is altered.