--- title: "Fluid Differential Pressure Sensors & Monitoring | Aethair" description: "Fluid differential pressure is the drop in pressure between the inlet and the outlet of a fuel or hydraulic filter vessel: how much pressure the liquid…" url: https://aethair.io/parameters/differential_pressure_fluid/ --- Measurements · Fluid / Level / Flow # Fluid Differential Pressure Also known as fuel filter differential pressure, filter vessel differential pressure, corrected DP Differential pressure across a fuel or hydraulic filter or filter/separator vessel, flow-corrected per ATA 103 / EI 1581 so it can be read against a fixed change-out limit. [Schedule a call](https://calendly.com/d/ctdd-mkr-v9v/aethair-demo-website) [Configure Fluid Differential Pressure Monitoring](https://aethair.io/build/?params=differential_pressure_fluid) At a glance psi Fluid / Level / Flow 1 way to measure it - **Thiamis** 1 external instrument What it is ## What is fluid differential pressure? Fluid differential pressure is the drop in pressure between the inlet and the outlet of a fuel or hydraulic filter vessel: how much pressure the liquid loses forcing its way through the element. It is reported in pounds per square inch differential (psi). Because the drop across a filter also rises with the flow through it, a raw reading taken at one flow rate cannot be compared with one taken at another. Aviation fueling therefore uses the **flow-corrected** value: the measured drop scaled to a reference flow, which gives one flow-independent number that reflects the condition of the element. This is the liquid-side sibling of room differential pressure: the same physics, but read across a filter vessel in a fuel line rather than between two rooms or across an air filter. In aviation fuel handling under **ATA 103** and **EI 1581**, differential pressure across each filter, filter/separator, and filter-monitor vessel is the running check that fuel is being cleaned as it is delivered. As an element captures water and particulate, it becomes harder for fuel to pass, so the corrected differential pressure climbs toward the vessel's change-out limit. An abnormally low or suddenly falling reading is the other warning: it can mean a ruptured or bypassed element, with fuel reaching the aircraft unfiltered. For airport fuel farms, refueler fleets, and hydrant operators, it is both a maintenance signal (change the element on evidence, not on the calendar) and a flight-safety check. How it is measured ## How Fluid Differential Pressure Is Measured A differential-pressure transmitter is plumbed across the filter vessel, one tapping upstream of the element and one downstream, and a flow meter reads the fuel flow through it so that the drop can be corrected to the reference flow. The **Parker Velcon FDPM** (Flow Differential Pressure Module) does both in one unit and computes the flow-corrected value itself. On a Thiamis gateway, it posts flow and differential pressure every reporting interval, so each fueling leaves a continuous record instead of a gauge reading written on a form. Methods and guidance [ATA 103](https://aethair.io/standards/ata_103/) An instrument on Thiamis 1 A third-party instrument connected to a Thiamis gateway, reporting into the same Environet account. ### Every device and option that measures Fluid Differential Pressure 1 | Device / option | Type | Base platform | Measures | | - | - | - | - | | [Parker Velcon](https://aethair.io/sensors/parker-velcon-fluid-fuel-quality/) · FDPM MK II, FDPM | Fluid & Fuel Quality | Thiamis | Fluid Differential Pressure [Flow Rate](https://aethair.io/parameters/flow/) | [Configure Fluid Differential Pressure Monitoring](https://aethair.io/build/?params=differential_pressure_fluid) Where it is monitored ## Solutions That Monitor Fluid Differential Pressure Each one links to the solution page showing what that industry measures it for. ### [Hydraulic & Fuel Cleanliness](https://aethair.io/solutions/industrial-fluids/) Often added ISO 4406 oil cleanliness and aviation fuel Related ## More in Fluid / Level / Flow [Water Level / Depth](https://aethair.io/parameters/water_level/) [Water Pressure](https://aethair.io/parameters/water_pressure/) [Volume (totalized)](https://aethair.io/parameters/volume/) [Flow Rate](https://aethair.io/parameters/flow/) [Fluid Particle Count (ISO 4406)](https://aethair.io/parameters/particle_count_fluid/) [Velocity](https://aethair.io/parameters/velocity/) Questions ## Fluid Differential Pressure FAQ Why does differential pressure matter in fuel filtration? Under ATA 103 and EI 1581, the pressure drop across filter-water separators and filter monitors shows that fuel is passing through clean elements at the expected resistance. A drop approaching the change-out limit means a loaded element; an abnormally low one flags a failed or bypassed element. Why is the differential pressure corrected for flow? The drop across a filter rises with flow rate, so a raw reading cannot be compared against a single fixed limit. Scaling it to a reference flow gives a number that changes only as the element loads, which is what ATA 103 and JIG procedures read against the limit. How is this different from room differential pressure? Room differential pressure is measured in air, in pascals, between two spaces or across an air filter, to keep a cleanroom or isolation room at its designed pressure. Fluid differential pressure is measured in a fuel or hydraulic line, in psi, across a filter vessel. They are listed as separate parameters because they answer different questions and are held to different standards. How do I monitor fluid differential pressure? Log a flow differential pressure module such as the Parker Velcon FDPM on a Thiamis gateway, and use the configurator to combine it with fluid particle count for a full fuel-cleanliness setup.