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Testing Pope 4 litre-per-hour dripper

June 29, 2019 — BarryK

I reported on testing of the Pope 2 litre/hour dripper, with various water heads:

The problem with that test is that the results are not accurate. The water head measurements are not right.

When I first setup the 2 l/h test, I assumed that when the tap is turned on, water would flow down and fill the pipe. Not so, it flowed down slowly and partially filled the pipe. Then I naively assumed the water head would still be accurate as the measurement from top-level in the holding tank, down to the dripper. Later on, I realised that is not so. The pipe has to be entirely filled with water.

So why didn't it fill? It seems that water flowed into the pipe, until the air pressure in the pipe equalled that at the tank tap outlet, and surface tension prevented air bubbles from getting out of the pipe. Perhaps this can be blamed on a fairly small opening inside the tap, for water to flow through.

Anyway, to test the 4 l/h dripper, I made sure that there was no air in the pipe. The setup is as per this earlier photo:


Except, now using the Pope 4 l/h dripper constructed with 13mm spurs on each end:


Making sure that the pipe was completely full for each measurement, now confident that the results are reasonably accurate:


This is very good. I am wanting about 1 litre/hour, so the "4 l/h" dripper is pretty much spot-on. I will be able to adjust flow by raising or lowering the water container. Though, I am hoping to find the "just right" height and construct that permanently, perhaps as part of the frame that holds the distiller. 

Tags: nomad