PLC Simulator
Basic
25 min

Flushing Valve Sequence

sequencervalveswatertimingfault

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Flushing Valve Sequence scenario preview

Briefing

A pipeline flushing system opens valves and runs a pump in a timed sequence to purge a pipe section. The sequence is: open inlet valve (5s), start pump (10s), open outlet valve + close inlet, drain through drain valve (3s), then close all. Each step uses a timed transition. ABORT immediately drops the process outputs and latches FAULT_LAMP; STOP acknowledges the fault and returns the controller to IDLE. A 30-second watchdog provides a second fault path if a sequence stalls.

Objectives

  • START_PB begins the flush sequence from IDLE
  • Sequence: VALVE_INLET open 5s → PUMP_RUN 10s → VALVE_OUTLET open + VALVE_INLET close → VALVE_DRAIN 3s → all closed
  • SEQ_COMPLETE_LAMP lights for 2s when sequence finishes successfully
  • ABORT_PB at any time drops every process output and latches FAULT_LAMP
  • STOP_PB drops the process outputs, acknowledges FAULT_LAMP, and returns to IDLE
  • FAULT_LAMP also latches if sequence does not complete within 30s

Hints

  • Use a step variable (IDLE, FILL, PUMP, FLUSH, DRAIN, DONE) with a TON per step
  • Each step timer resets on entry; transition fires on Q output of the TON
  • ABORT_PB resets every active step and sets FAULT_BIT; STOP_PB resets both the steps and FAULT_BIT
  • Keep the fault reset separate from the ABORT rung so the alarm remains visible for acknowledgement

I/O Table

Inputs

START_PB

Start push-button (momentary)

BOOL · %I0.0

STOP_PB

Stop push-button (momentary)

BOOL · %I0.1

ABORT_PB

Abort push-button (drops all)

BOOL · %I0.2

Outputs

VALVE_INLET

Inlet solenoid valve

BOOL · %Q0.0

VALVE_OUTLET

Outlet solenoid valve

BOOL · %Q0.1

VALVE_DRAIN

Drain solenoid valve

BOOL · %Q0.2

PUMP_RUN

Flush pump run contactor

BOOL · %Q0.3

SEQ_COMPLETE_LAMP

Sequence complete indicator

BOOL · %Q0.4

FAULT_LAMP

Fault indicator lamp

BOOL · %Q0.5

Your program will be tested against:

All test cases run automatically when you submit. Assertions are hidden until you pass.

  1. #1VALVE_INLET opens when START_PB pressed

    START_PB -> VALVE_INLET energises in step FILL

  2. #2Pump runs after inlet step (5s)

    After 5s in FILL, PUMP_RUN energises

  3. #3ABORT_PB drops all outputs immediately

    Mid-sequence abort clears all valves and pump

  4. #4Outlet and drain valves energise in their correct phases

    The outlet opens for FLUSH, then the drain joins it only during DRAIN

  5. #5Full sequence completes and lights SEQ_COMPLETE_LAMP

    Run full sequence: FILL(5s)+PUMP(10s)+FLUSH(0s)+DRAIN(3s) -> SEQ_COMPLETE_LAMP

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Runnable simulator field guide

Flushing-valve PLC sequence: test checklist

Direct answer

The learner can prove the intended route before flow, handle missing valve or flow feedback and leave the system in a declared post-flush state.

Written for process and water-system learners sequencing isolation, flushing, drain and return-to-service states with explicit evidence.

a guarded water-based process training skid used to test dosing, heating, flushing, valve, pump and instrument sequence evidence while studying flushing route, valve proof, flow confirmation and controlled completion
System map / 02

NODE 01observable

Scenario setup

System boundary, source and destination, isolation valves, flush valve, drain route, pump or pressure source, valve feedback, flow proof, duration or volume criterion, hold, abort and return state.

NODE 02observable

I/O and state map

Operator request through route selection and valve commands to confirmed positions, flow establishment, completion evidence, controlled stop, drain or isolation and record.

NODE 03observable

Normal run

The declared route is proven before flushing and completion occurs once using the required time, volume or quality evidence.

NODE 04observable

Boundary run

Wrong route, valve fails open or closed, no flow, low pressure, blocked drain, timeout, interrupted flush, power loss and ambiguous return state.

NODE 05observable

Injected fault

A route, state, valve, feedback, pump, pressure, flow, completion, hold or recovery mismatch.

NODE 06observable

Target check

The production procedure reviewed for process, quality, environmental and equipment requirements and validated on target.

Answer surface / 07

What should a flushing sequence verify before opening flow?

Verify the correct source, destination, isolation and drain route plus required valve and equipment availability before allowing flow.

Should a flushing sequence finish on time alone?

Only if the approved process defines time as sufficient; many applications also require volume, flow, conductivity, turbidity, sample or other quality evidence.