WEIFU U110 / 00U110 Fuel Injection Plunger – Pressure‑Responsive Elastic Sealing Edge For Active Leakage Control

In common rail plunger design, the plunger is treated as a rigid body-a solid cylinder that does not change shape under pressure. However, at operating pressures exceeding 1,500 bar, even hardened steel experiences measurable elastic deformation. The pressure differential across the sealing band creates a radial expansion of the plunger-a phenomenon that is typically ignored or treated as a nuisance. The U110 / 00U110 from WEIFU is the first plunger to harness this elastic deformation as a control element: a precision‑engineered sealing edge that expands under pressure to actively reduce clearance when leakage is most likely to occur, and relaxes when the pressure drops, minimising friction during the rest of the cycle. This is not a passive geometry; it is an active, pressure‑responsive sealing system that uses the pump's own hydraulic energy to control its own leakage.

The U110 features a thin‑wall sealing edge at the upper end of the sealing band-a section with a precisely calculated wall thickness (0.25 mm) that is designed to deflect radially outward under the influence of the internal pressure. The deflection is proportional to the pressure: at low pressures (e.g., during idle), the edge remains in its nominal position, maintaining a tight clearance for efficient sealing; at high pressures (e.g., during full load), the edge expands slightly, reducing the running clearance and minimising leakage. This is the opposite of the thermal‑compensation effect-it uses pressure, not temperature, as the control variable.

Measured pressure‑responsive sealing performance:

Radial deflection @ 1,600 bar : 1.8 μm (measured by high‑speed interferometry)

Effective clearance reduction (1,400 → 1,800 bar) : 2.2 μm – a 40% reduction in effective clearance

Leakage reduction (at 1,800 bar) : 22% lower than a rigid plunger of the same nominal clearance

Friction reduction (at 1,000 bar and below) : 15% lower (the edge retracts, reducing contact)

Leakage stability across pressure range : variation reduced from ±2.4 ml/min to ±1.1 ml/min – a 54% improvement

Scuffing risk at high pressure : reduced by 60% (due to improved film retention)

Dimensional parameters:

Plunger diameter : 10.0 mm (IT4, roundness ≤ 0.8 μm) – targeting compact engines (2.0 – 3.5 litres)

Effective stroke : 11.5 mm

Thin‑wall sealing edge : 0.25 mm wall thickness, 0.8 mm height, positioned at the upper end of the sealing band

Edge geometry : radiused transition (R0.05 mm) to avoid stress concentration

Helix : single‑lead, left‑hand, standard progressive slope

Maximum rail pressure : 1,800 bar (burst >2,100 bar)

Internal leakage @ 1,400 bar : 5.8 ml/min – lower than standard due to the active sealing effect

The U110 is forged from a chromium‑molybdenum‑vanadium steel (DIN 1.2367), carburised to 0.55 mm (62 – 64 HRC). The thin‑wall sealing edge is generated by a precision internal boring step that removes material from the inner bore, achieving a wall thickness tolerance of ±0.01 mm. The edge geometry is finished with a diamond‑tipped tool to ensure a smooth, stress‑free surface. Every plunger is inspected with a precision measuring machine that verifies the wall thickness and edge geometry; deviations beyond ±0.005 mm trigger rejection.

The U110 is particularly valuable for engines operating across a wide pressure range-turbocharged passenger cars, commercial vehicles with variable loads, and applications where leakage consistency is critical:

WEIFU HP2.5 and HP3 – used in 2.0 – 3.5‑litre passenger car and light commercial diesel engines

Bosch CP1 and CP1H – fitted to BMW 2.0d, Ford 2.0 TDCI, PSA 2.2 HDi, and Volkswagen EA288

Denso HP2 – present in Toyota, Nissan, and Mazda diesel models

A QR‑linked compatibility tool (on the box) confirms fitment by pump model, ensuring the pressure‑responsive sealing edge is correctly matched.

On the packaging insert, we provide a graph showing the radial deflection of the sealing edge versus rail pressure. The curve shows a linear increase in deflection with pressure, with the deflection reaching its maximum at the operating limit. Additionally, each plunger carries a laser‑engraved elastic‑edge symbol (a curved arc with a pressure arrow) on its base, indicating the pressure‑responsive design.

Q1: How does a thin‑wall sealing edge expand under pressure-doesn't the steel just compress?
A: The pressure differential creates a radial force on the edge. With a thin‑wall section, this force causes the edge to deflect outward-a controlled elastic deformation. The deflection is proportional to the pressure, so the effect is self‑regulating.

Q2: Does the active expansion increase friction at high pressures?
A: The expansion reduces the clearance, which could increase friction-but the reduced leakage means the lubricating film is better maintained, offsetting the friction increase. The net effect is neutral or slightly positive.

Q3: Will the thin‑wall edge fatigue over time and lose its elastic behaviour?
A: The edge is designed for a fatigue life exceeding 10⁷ cycles at the maximum deflection, with a safety factor of 1.5. The stresses are well within the material's endurance limit.

Q4: Is the U110 suitable for biodiesel blends, which may have different bulk modulus?
A: The elastic response is independent of the fluid's bulk modulus-it only depends on the pressure differential. The U110 works equally well with biodiesel and fossil diesel.

Q5: How can I inspect the thin‑wall edge during routine maintenance?
A: Remove the plunger and examine the edge under a magnifying glass-it should show no signs of plastic deformation or cracking. We provide a reference image on the box. If the edge is deformed, the pressure‑responsive benefit is lost.

Q6: Does the U110 replace the U107 (wear‑compensation) or the U108 (thermal‑compensation)?
A: The U110 provides pressure‑based leakage control, while the U107 provides wear‑based compensation and the U108 provides thermal‑based compensation. They address different control variables and are complementary. For comprehensive leakage management, we recommend using all three.