pump — pressure_hydraulics (accumulator-precharge)
Physics
Section titled “Physics”A hydraulic accumulator stores energy by compressing a nitrogen-filled bladder or piston against hydraulic fluid; its precharge (the nitrogen pressure with the hydraulic side at zero) sets how much usable fluid volume it can deliver before system pressure sags. A slow nitrogen leak past the bladder or valve core lowers the precharge over weeks to months, which shows up first as a faster-than-normal pressure droop between pump cycles and eventually as the pump short-cycling to keep up with demand. A pressure transducer on the accumulator’s hydraulic port (or a dedicated gauge port) reads system pressure continuously, and the pressure trace’s droop characteristics between pump strokes track precharge loss. This binds to the generic run/idle/off/fault threshold-state detector repurposed for pressure-level classification: holding above run_above during normal operation is charged, dropping below off_below between pump cycles (deeper and/or longer than normal) is depleted/fault-risk, and staying there past fault_after_s is a confirmed fault consistent with precharge loss. System pressure settles within a second or two of a pump stroke, but the state machine only needs to resolve the trend of a precharge leak developing over days to weeks, so sampling at 2 Hz gives comfortable margin while a 1 Hz low-pass ahead of classification removes stroke-to-stroke ripple.
Sensor
Section titled “Sensor”- Spec: hydraulic pressure transducer, threaded port, 0-5000 psi range, 4-20 mA
- Signal: scalar ([psi]), range n/a
Example parts
Section titled “Example parts”- ifm electronic PT5404 pressure transmitter (0-580 bar / 0-8410 psi, 4-20 mA, G1/4 port)
- Ashcroft G1 pressure transmitter (0-5000 psi, 4-20 mA, 1/4 NPT male)
- Gems Sensors 3100 series pressure transmitter (0-5000 psi, 4-20 mA, 1/4 NPT)
Mounting
Section titled “Mounting”Install the transducer in a tee fitting on the accumulator’s hydraulic-side gauge port or a spare port on the manifold immediately adjacent to the accumulator, so the reading reflects accumulator-side pressure rather than pump discharge pressure measured further downstream. Torque to the fitting manufacturer’s spec and pressure-test the new joint at system pressure before returning the unit to service.
Wiring
Section titled “Wiring”4-20 mA two-wire loop to a 24 V DC loop-powered analog input on the edge box’s DAQ module; route the shielded twisted-pair cable away from the pump motor’s power leads and ground the shield at the DAQ end only to avoid a ground loop.
Validation
Section titled “Validation”with the system at normal operating pressure, read the transducer’s live psi value on the edge box dashboard against a calibrated test gauge tee’d into the same port, then isolate the pump momentarily and observe the pressure droop rate to confirm it matches the accumulator’s known-good precharge droop curve, and that the detector transitions to depleted/fault if the droop is abnormally fast
Expected: transducer reading within +/-2% of the test gauge, and the detector reports depleted/fault state only when droop behavior deviates from the accumulator’s known-good precharge curve
Safety notes
Section titled “Safety notes”- hydraulic fluid under system pressure (often 1500-5000+ psi) can penetrate skin through a pinhole leak and cause a serious fluid-injection injury with no visible external wound; never attempt to feel for a leak with a bare hand
- a charged accumulator stores energy even when the pump is off and locked out; de- pressurize and bleed down the accumulator per its rated procedure before opening any fitting or installing the tee for the transducer, and never work on an accumulator that has not been confirmed at zero pressure
- verify the transducer’s pressure rating and port thread exceed the accumulator’s maximum working pressure before installation; a transducer rated below system pressure can rupture
90–320 USD, difficulty 3/5, ~60 min install downtime.