Filter Differential Pressure Log: What to Record

A filter differential pressure log helps explain why a liquid filter needs attention. Recording a pressure number alone is not enough: a change in flow, liquid temperature or feed condition can change the reading without proving that the filter is exhausted.

This practical record sheet is for operators reviewing liquid filter bags and melt blown filter cartridges. Use it alongside the equipment manual and your site’s approved operating procedure.

Define exactly what you are measuring

Differential pressure, written as ΔP, is upstream pressure minus downstream pressure. Both readings must use the same units and pressure reference and be taken at comparable times. Label the measurement points on the equipment drawing. Readings across an entire housing include the restrictions between those points; they are not necessarily the pressure drop across the media alone.

Do not confuse vessel operating pressure with filter differential pressure. A high inlet pressure is not, by itself, evidence of a blocked element. Likewise, a vessel pressure rating is not a permitted differential pressure for the installed bag or cartridge.

Create a clean-filter baseline

After an approved installation and startup, record a baseline once the process reaches a stable, representative condition. Note the exact element code, quantity installed, batch, liquid, flow and temperature. Record whether the readings represent startup, normal production or another operating state.

Keep the same measurement locations for later comparisons. Confirm instrument suitability and condition under the site’s instrument procedure. If two pressure gauges cannot reliably resolve the small difference being measured, ask the instrument specialist whether a suitable differential-pressure instrument is needed.

Use this log structure

Interpret trends under comparable conditions

A gradual rise in ΔP at similar flow, temperature and feed conditions can indicate accumulating retained material. A sudden increase deserves an operating-condition check as well as a filter assessment. For example, a colder, more viscous liquid or a higher flow can increase resistance. Do not label every increase as fouling.

A decrease is not automatically an improvement. First check whether flow fell or the process changed. If outlet quality worsened at the same time, investigate the installation and element condition under the approved procedure. For a bag system with poor filtration after replacement, use the separate filter bag bypass diagnosis guide.

Manufacturer curves must be read with their test conditions. Eaton’s LOFTREX cartridge datasheet, for example, presents water pressure-drop curves at a stated temperature and provides a viscosity adjustment note. This illustrates why the fluid and test basis matter; those curves are not INCEFILTER product ratings or a universal correction for every process.

Set action limits for the exact assembly

Obtain the approved replacement criterion and maximum allowable differential pressure for the exact filter, support arrangement and operating temperature. The maximum structural limit is not a target at which to routinely operate. Use the equipment owner’s earlier action limit and any outlet-quality or process limits that apply.

Do not raise pump pressure simply to extend a run. Never open a pressurized housing to investigate a reading. Trained personnel must follow the isolation, depressurization, draining and handling instructions for the equipment and liquid.

Turn the record into a better filter inquiry

Compare several representative runs before requesting a different grade or configuration. Send INCEFILTER the current part number, housing details, liquid composition, flow and temperature range, baseline and end-of-run ΔP, processed volume where measured, and the outlet-quality requirement. Identify whether the problem is short run time, excessive clean pressure drop or poor quality.

Request a product-specific filtration review with those records. They support a more useful selection discussion than a micron number alone; they do not establish a guaranteed service life.

Technical reference

Eaton: LOFTREX industrial filter cartridge technical data sheet. Cited for its stated flow, temperature and viscosity basis only.