Offline Filtration Cart

Overview

An offline filtration cart is a mobile fluid conditioning unit used to remove contamination from hydraulic reservoirs and circuits during maintenance. It is essential for meeting ISO 18/16/13 (or finer) cleanliness targets in high-performance systems. The cart includes a Pump Unit (gear pump, 5–50 L/min) powered by Drive Motor (electric motor), pushing fluid through two Filter Cartridge Housing stages (tank return and offline cartridges). An optional Particle Counter provides real-time cleanliness verification. The Hose Reel stores 50–100 m of quick-disconnect hose, enabling both suction-side (removing fluid from tank) and circuit-side (filtering active system) operations.

Pump and manifold circuit

The Pump Unit is a low-cost internal gear pump (no load-sensing control); displacement ranges 5–30 cc/rev, delivering 5–40 L/min at 100–210 bar. Pump outlet flows through a Control Manifold containing a pilot-operated Relief Cartridge (adjustable 50–200 bar) and a one-way Check Cartridge preventing backflow when the pump stops. Manifold galleries route flow to the filter stages and back to tank. A small Pulse Damper Accumulator (0.5–2 L) dampens pump ripple (50–300 Hz), reducing noise and pulsation transmitted to hose.

Dual filter stages

Tank return filtration (offline mode): fluid is drawn from the reservoir (suction hose in tank) and pushed through a Filter Cartridge Housing with a 10 µm microglass element, returning to tank. This low-pressure stage (< 10 bar) conditions the bulk fluid, removing silt, water, and wear debris over 4–8 hour cycles. A thermal Filter Bypass opens at 3.5 bar ΔP during cold-start, allowing bypass flow until the fluid warms and viscosity drops.

Circuit-side filtration: The cart can also be connected inline between pump and actuators for active system cleaning. In this mode, the pump outlet supplies the filter cartridge, and return flow feeds back to tank. This is more aggressive but risks contaminating the active circuit if the filter is saturated; operators monitor Flow Meter and Particle Counter continuously.

Particle counter and fluid diagnostics

The optional Particle Counter is a laser-based optical sensor that samples fluid passing through a viewing chamber at constant flow rate. It counts particles in three size ranges (4–6 µm, 6–14 µm, > 14 µm) per ISO 4406 standard, displaying the result as a three-number code (e.g., 18/16/13 = < 640 particles > 4 µm, < 320 particles > 6 µm, < 20 particles > 14 µm). Trending over time shows fluid cleanliness improvements; a cart run that improves fluid from 20/18/15 to 18/16/13 indicates the offline filtration is effective.

Flow meter and usage tracking

The Flow Meter is an inline turbine or electromagnetic meter indicating real-time flow (L/min) and total volume processed (display logs hours run and liters circulated). This data is useful for scheduling element replacement: a saturated element shows increasing pressure drop and decreasing flow; when ΔP exceeds 3.5 bar and flow drops 20% below baseline, the element is replaced. Typical element life is 50–200 operating hours depending on fluid condition and flow.

Motor and power options

Portable carts use 24 VDC electric motor (powered by rechargeable LiFePO4 battery) or 1-phase 115 V AC (shop outlet). Larger fixed installations use 3-phase 208 V AC motor (2–3 kW) and are permanently plumbed to the main reservoir. Startup is controlled by a simple run/stop button; a pressure relief valve protects the pump if suction line is kinked (pump will reach maximum pressure in < 5 seconds if outlet is blocked).

Hose and coupling strategy

The Hose Reel stores 50–100 m of suction and discharge hose (color-coded or labeled). Suction hose is larger diameter and shorter (< 1 m) to minimize inlet vacuum; discharge hose is typically −16 SAE (10 mm ID) for 50 L/min systems. Quick-disconnect couplings (flat-face, ISO 16028 flat-faced) prevent spill when disconnecting; male couplings on the cart, female on tank/system connections.

Maintenance and serviceability

Annual inspection includes: pump displacement verification (measure actual L/min at rated pressure; compare to nameplate; shortfall > 10% indicates gear wear), motor current draw under load (compare to nameplate; increase > 10% indicates pump friction), and filter element inspection (pleats for tears or media degradation). Fluid in the cart reservoir should be kept clean (ISO 18/16/13 minimum) and changed annually or when particle count exceeds 20/18/15. Ball bearings in the hose reel and pump support are grease-lubricated; apply lithium complex grease at 500-hour intervals.

Standards and performance targets

Offline filtration equipment is certified to ISO 16/814 (industrial hydraulic fluid cleanliness achievement test). A cart conditioning 10,000 L of 22/20/17 fluid to 18/16/13 requires approximately 20–30 operating hours of offline circulation. Final fluid condition is verified by laboratory particle count (ISO 4406) and Karl Fischer titration (water content < 200 ppm for mineral oil).