Open End U‑Tube Manometer

Open-End U-Tube Manometer

An open-end U-tube manometer compares gas pressure in a vessel (p_g) with atmospheric pressure (p₀) using a liquid column (here, mercury; ρ ≈ 13 593 kg/m³). The vertical level difference h between the two free surfaces converts a pressure difference into a measurable height: Δp = p_g − p₀ = ρgh.

How to use the simulation

1. Move the Gas Pressure slider. As p_g increases, particle motion in the tank intensifies (visual cue of higher pressure).
2. Watch the levels: the right arm is open to atmosphere (p₀). Thin lines mark each free surface; the double-headed arrow is h.
3. Read the numbers: p_g (kPa), p₀ (fixed at 101.3 kPa), and calculated h (cm). For mercury, 1 kPa ≈ 0.75 cm of Hg.
4. Explore cases: set p_g ≈ 101.3 kPa → h ≈ 0; raise p_g by ~8.7 kPa → h ≈ 6.5 cm; lower p_g below p₀ → the connected arm rises.

Quick example
Given p₀ = 101.3 kPa and p_g = 110.0 kPa:
Δp = 8.7 kPa = 8700 Pa
h = Δp/(ρg) = 8700/(13 593 × 9.81) m ≈ 0.065 m = 6.5 cm.

Key takeaways

• Gauge vs absolute: This tool shows gauge difference Δp. Absolute gas pressure would be p_abs = p₀ + (p_g − p₀)
• Linear relation: For a fixed liquid and g, h ∝ Δp.Role of density: Smaller ρ (e.g., water) → larger h for the same Δp.
• Correct measurement: h is the vertical separation of free surfaces (not along the bend).