A rapid valve closure on a 4 km rising main slams it to ~32 bar and into deep vacuum — real water hammer. An air chamber stops the column separation at the pump manifold, and a power-failure pump-trip hands the pipe-stress engineer a 368 kN CAESAR II force file.
~32 bar
peak Joukowsky surge from a 1 s valve closure (closure-time-sensitive)
−9.2 → −0.9 bar
pump manifold: column separation removed by the air chamber
The system
A 4 km rising main, lifting 85 m
A suction reservoir feeds a pump that drives water up a long DN450 rising main to an elevated delivery reservoir. The Korteweg wave speed in this steel main is 1248 m/s — so a disturbance at the pump reaches the far end and reflects back in seconds. That is exactly when water hammer bites.
Fluid
Water (998 kg/m³)
Main
DN450, ~4 km rising main
Static lift
85 m to elevated reservoir
Wave speed
1248 m/s (Korteweg, DN450 / 12 mm steel)
The headline — real water hammer + column-separation protection
A 1-second valve closure slams the main to ~32 bar
A rapid (1-second) valve closure drives the rising main to a ~32 bar Joukowsky surge and into deep vacuum — genuine, closure-time-sensitive water hammer (32.8 bar at a 0.2 s closure, 19.8 bar at 6 s). Unprotected, the pump manifold drops to −9.2 bar, a severe column-separation risk; a single air chamber teed at the pump discharge stops the separation there (−0.9 bar). The same run also quantifies where the far mains still cavitate — exactly the insight that drives the full surge-protection design.
Valve-closure water hammer — peak surge + the air chamber's column-separation protection
Parameter
Value
What it proves
Peak surge (1 s valve closure)
~32 bar
Genuine Joukowsky water hammer — closure-time-sensitive (32.8 bar at a 0.2 s closure, 19.8 bar at 6 s). Not a static artefact.
Pump manifold (HEADER) — without chamber
−9.2 bar
Deep sub-vapour at the pump discharge → column-separation risk (valve-closure run, no device).
Pump manifold (HEADER) — with air chamber
−0.9 bar
The air chamber teed at the pump discharge stops the column separation at the manifold (dossier path VC-039/040).
Worst far-main vacuum (RM4)
−43.8 → −29.0 bar
The far main still cavitates — the transient analysis quantifies exactly where additional surge protection is needed. Real engineering, not a fairy-tale fix.
Source: the valve-closure + air-chamber run (the wired surge-device path, dossier VC-039/040).
The danger — an unprotected pump trip
Power fails, the pump trips, the column slams back
A separate run models the real failure mode: power loss. The pump coasts down on its four-quadrant Suter characteristic and flywheel (GD²), flow reverses, and the rejoined column slams back as a ~23.6 bar up-surge (max head 240 m) while the upper main dips below vapour pressure. DekEn exports the transient force history as a CAESAR II force file so the pipe-stress engineer can run the stress check on the same loads.
Unprotected pump-trip (power-failure) transient
Parameter
Value
What it proves
Up-surge (pump-trip, unprotected)
~23.6 bar
Power-failure 4Q Suter + GD² pump-trip transient; up-surge near the pump.
Down-surge (gauge)
~−5.3 bar
Head-derived sub-vapour pressure — a column-separation RISK indicator, not an achievable pressure.
Max head
240 m
Peak hydraulic grade line during the unprotected pump-trip transient.
Peak transient thrust
368 kN
Peak unbalanced hydraulic force at the pump discharge — the load the pipe stress engineer needs.
CAESAR II force file
5 TIME_HISTORY blocks
Production force export, ready to hand to the pipe-stress engineer for a stress run.
Source: the unprotected power-failure pump-trip run (network MOC, 4Q Suter + GD²).
What this proves vs the competition
Transient surge analysis with a four-quadrant pump trip, air-chamber cushioning, and a CAESAR II force-file handoff is the territory of AFT Impulse and PIPENET Transient — expensive desktop seats. DekEn runs the same network method-of-characteristics transient in a browser tab.
