I think I've got a measurement issue but I'd like to make sure that what I am seeing is not a "real" phenomenon...
In the air intake of one of our gas turbines we have installed 2 sets of filters back-to-back so that one of them sits the opposite way to normal, a bit like the picture below;
/ || \
3| ||2 | 1 <-Air flow
\ || /
With differential pressure (dP) measurement points as indicated by the numbers 1, 2, and 3, in order to give an indication of filter loading.
With this setup, we are seeing an increase in dP across the second filter (3-2) but the dP across the first filter (1-2)is remaining roughly constant (there was a very minor increase in dP when first installed but this has since levelled off). When the filters are examined there is some fouling on both filters, though neither appear saturated.
Could the apparently static dP be giving a "false" reading for loading due to the proximity of the probe to the surfaces of the filters? Or, is this a true phenomenon caused by the closeness of the filters to one another - i.e. that the second filter is actually loading before the 1st somehow?
Also, does anyone know if positioning filters this close to one another reduces the effeciveness of the filters?
The filters are a box-type W - shape.
Any ideas are welcome.
Thanks in advance.