The Importance of Differential Pressure
The difference between the inlet and outlet pressure of a
filter housing is called differential pressure and is represented by the symbol
ΔP or Delta P. When fuel encounters resistance the pressure will drop – the
measurement of the drop is ΔP. The high
pressure reading is on the inlet side and the low pressure reading the outlet
side. It is essential to measure ΔP as
it is the primary indicator of the filter’s condition.
There are a few major factors that affect ΔP:
A filter will increase ΔP. However, a clean
filter regardless of type should read no more than 2 or 3 pounds of ΔP when
Water contamination will slow the flow and
Particulate contamination increases ΔP.
Microbial contamination increases ΔP
A bypassed filter (i.e. hole in filter or filter
failure) will cause a drop in ΔP. It should be remembered filters NEVER get
better over time. The ΔP will always rise with use.
Higher flows can create higher pressure drops.
Differential pressure should rise slowly and steadily over
time until it reaches its limit. The standard ΔP limit of a filter is 25
pounds. As the ΔP moves closer to the limit, it can quickly rise. This is due
to contaminants clogging the filter pores and creating pressure. Sudden premature rises in ΔP should be
investigated. An inline contamination monitor can help to identify issues and
problems associated with ΔP.