Hydraulic Circuit Simulator and Trainer

Welcome to the Hydraulic Circuit Simulator and Trainer — a free, browser-based hydraulic systems simulator designed for mechanical engineering students, fluid power technicians, vocational instructors, and maintenance engineers. This tool serves as a powerful FluidSIM online trainer alternative, providing interactive ISO 1219 schematic building, real-time oil flow animation, and comprehensive learning modes — all without installation, signup, or licensing fees.

Whether you are a beginner learning Pascal’s law or an advanced student designing multi-actuator circuits, this hydraulic trainer bridges the gap between textbook theory and hands-on practice. The simulator features 50 hydraulic components, 10 pre-built circuit templates, and 4 interactive learning modes (Simulate, Explore, Practice, Quiz).

1. Select a mode — Choose Simulate to build circuits, Explore to study concepts, Practice for calculation problems, or Quiz for self-assessment.
2. Load a pre-built circuit — Click any of the 10 circuit templates (Meter-In, Meter-Out, Regenerative, etc.) to instantly populate the canvas with a working circuit.
3. Pick your units — Use the SI / Imperial toggle next to the mode tabs to switch every readout and gauge between bar ↔ psi, L/min ↔ gpm, kW ↔ hp, kN ↔ lbf, and mm/s ↔ in/s. All calculations stay in SI internally.
4. Or build from scratch — Click a component in the left palette, then click anywhere on the canvas to place it.
5. Connect components — Click a port (small circle) on one component, then click a port on another to draw a hydraulic line. Click the empty canvas between ports to add waypoints for custom routing.
6. Run the simulation — Click the Run button or press Space. Animated particles show oil flow direction and speed. Pressure readings appear on each connection.
7. Control actuators — Click directly on a DCV (directional control valve) to switch its spool position between Extend, Center, and Retract.

This hydraulic systems simulator includes all essential fluid power components drawn to ISO 1219 standard:

Power Source: Power Unit (Pump) — configurable Max/Rated Pressure (50–350 bar) and flow rate (5–100 L/min). Read that first parameter carefully: a positive-displacement pump is a flow source, not a pressure source. It does not “make 150 bar” — it delivers litres per minute, and the pressure that results is whatever the load and the relief valve allow. The rated pressure is simply the ceiling the unit is built to survive.

Directional Control Valves: DCV 4/3 (4-port, 3-position with Extend/Center/Retract), DCV 3/2 (3-port, 2-position for single-acting cylinders), and 2/2 Way Valve (on/off shut-off).

Flow Control: Flow Control Valve (1–60 L/min), Throttle Valve (5–100% opening), Fixed Orifice, Check Valve, Pilot Check Valve, and Shuttle Valve. The plain Flow Control Valve is a needle valve — it is not pressure compensated, so it obeys the orifice law Q = Q_set × √(ΔP/100 bar). Increase the cylinder load and you will see the actuator slow down, because a higher load leaves less pressure drop across the needle. Swap it for the Pressure-Comp FC and the speed stops changing — its compensator spool holds a constant 7 bar across the metering orifice whatever the load does. That side-by-side comparison is the entire reason compensated valves cost more. The Fixed Orifice follows ΔP ∝ Q²/d⁴, so halving the bore multiplies the drop by sixteen.

Pressure Control: Relief Valve (50–350 bar), Proportional Relief, Pressure Reducing Valve (20–200 bar), Sequence Valve (30–300 bar), and Counterbalance Valve with a selectable catalogue pilot ratio (1.5:1, 3:1, 4.5:1, 8:1, 10:1). The counterbalance spool is solved on a full force balance — it cracks when load pressure + (R × pilot pressure) ≥ setting + (R+1) × back pressure. The back-pressure term is why a restricted return line makes a real over-centre valve chatter or refuse to open, and it is the reason counterbalance valves are so often specified with an external drain.

Actuators: Single-Acting Cylinder (with a sized return spring), Double-Acting Cylinder (configurable bore, rod, stroke, and Load in kN), Telescopic Cylinder, Rotary Actuator, and Hydraulic Motor (5–100 cm³/rev with a Load Torque in N·m). Cylinders are solved on a full piston force balance, not the schoolbook p = F/A:

extending: η_m (p_capA_bore − p_rodA_ann) = F   ·   retracting: η_m (p_rodA_ann − p_capA_bore) = F

Both faces are wetted, so whatever the exhausting side is pushing against comes straight back out of the driving side. A mechanical efficiency of η_m = 0.90 (seal and bearing friction) and a motor volumetric efficiency of η_v = 0.95 (internal leakage) are applied throughout, which is why the simulator asks for slightly more pressure and gives slightly less speed than an ideal hand calculation. Two consequences you can see on screen:

• Pressure intensification. Meter the rod-side exhaust of an 80/45 cylinder and the rod side climbs to roughly 1.46 × the cap side, because A_bore/A_ann = 1.46. The cylinder overlay prints this back-p figure live. It is the classic reason a meter-out circuit can burst a rod-side hose rated for the pump pressure.
• Over-running loads. The Load parameter now goes negative. A negative load is an aiding load — a suspended weight pulling the rod out — and with one the cap-side pressure collapses toward zero. Nothing in the circuit resists the load, and the simulator says so. Fit a counterbalance valve or meter the exhaust and the actuator is controlled again. That is the whole job of an over-centre valve, and it cannot be demonstrated with a load that is only ever positive.

A load beyond the available supply pressure still stalls the actuator. The single-acting cylinder only springs back if its return spring is actually stronger than the load — a spring sized for seal friction cannot lift a heavy weight, and the simulator refuses to pretend otherwise. The motor shows live RPM and torque, with T = ΔP × D × η_m / 20π and n = Q × 1000 × η_v / D.

Utility: T-Connector, Accumulator (20–200 bar precharge, 1–50 L), Pressure Gauge, Flow Meter, and Filter. The accumulator follows Boyle’s law — p_gas = p_pre / (1 − x), where x is the fraction of gas volume displaced by oil — so the last litres in cost far more pressure than the first, exactly as on a real nitrogen bladder. It charges whenever line pressure exceeds its gas pressure (a live % badge shows the charge state) and automatically discharges as an emergency supply if the pump fails — try it with the Pump failure fault to see ride-through in action.

Place components by clicking in the palette then clicking the canvas. Move by dragging. Connect ports by clicking port circles. Add waypoints by clicking empty canvas during connection. Drag segments to adjust routing. Right-click a connection to clear waypoints.

10 Pre-Built Circuit Templates: Meter-In, Meter-Out, Regenerative, Sequence, Bleed-Off, Counterbalance, Safety, Priority, Sync Cylinders, and Precision Speed.

Simulation features: Animated oil flow particles, pressure computation, cylinder extension/retraction at true physical speed (a 300 mm stroke at 100 mm/s completes in 3 s, matching the speed readout), motor rotation, live readout panel, interactive DCV control (click to switch spool position), and circuit validation warnings. Flow restrictors follow the orifice law — pressure drop rises with the square of flow.

Where the pressure actually is. The supply branch is solved backwards from the load, so a gauge tapped downstream of the DCV reads the pressure the load demands, not the relief setting — a 30 kN load on an 80 mm bore reads about 66 bar even with a 150 bar power unit, and the System Pressure readout follows it down. Centre the DCV and the same line jumps to the relief setting, because a deadheaded pump has nowhere else to send its flow. Put a needle valve in the pressure line (meter-in) and the gauge upstream of it stays at relief while the gauge downstream sits at load pressure — the difference between the two is exactly the energy being burned as heat across the orifice. The Hydraulic Power card is computed from the real line pressure, so it drops when the load drops instead of quoting the pump nameplate.

Component manipulation: Rotate 90° (right-click, toolbar, or Shift+R), Duplicate (right-click), Delete (right-click, toolbar, or Delete key), Undo (Ctrl+Z, up to 30 states), Edit Parameters (right-click → Info). In the properties panel every slider is paired with a type-in number box — enter an exact value (e.g. 63 mm bore) and press Enter; out-of-range values clamp automatically.

Explore mode provides an interactive hydraulic reference library across Fundamentals (Pascal’s Law, Flow-Pressure-Power, Hydraulic Advantage, Continuity Equation), Components (10 detailed entries), Circuits (4 topologies with descriptions and applications) and Applications (4 worked industrial case studies).

Practice presents 12 randomised calculation problems covering cylinder extend and retract force, extend and retract speed, pump flow, system power, relief-valve setting, regenerative circuits, area ratios, and swept volume. Step-by-step solutions provided.

Quiz draws a 5-question assessment at random from a 15-item pool (8 MCQ + 7 numeric) with immediate feedback, correct answers, and final score classification.

Use the mark-bar above the canvas to annotate your circuits:

• Move tool — select, move, resize, duplicate, rotate, and delete annotations. Double-click a text label to edit it.
• Sketch tool — freehand drawing. Pick colour and width from the dropdown. Stays active after each stroke for continuous drawing.
• Shape tool — draw rectangles, circles, ellipses, arrows, lines, double-arrows, or text labels. Pick shape type, colour, width, and fill from the dropdown.
• Toggle annotations — show/hide all annotations without deleting them.
• Clear annotations — remove all or a category (sketches only, shapes only).
• Export PNG — save the canvas (with annotations) as a PNG image.

Drawing to the standard — ISO 1219-2 layout aids

Three toolbar buttons turn a working circuit into a drawing you could put in a manual.

• ID — shows the ISO 1219-2 identification code on every component: <circuit><letter><number>. Circuit 0 is the power supply and each actuator gets its own working circuit from 1; the letter says what the thing is (P pumps, A actuators, V valves, S sensors, Z accessories, M prime movers). So 0P1 is the pump, 0V1 the system relief, 1A1 the first actuator and 1V2 the second valve serving it. The circuit numbers are worked out from the pipework, not typed in — each actuator claims whatever is nearest to it, while the supply group stays circuit 0. These codes are what let an engineer name a part over the phone, and they are mandatory on a compliant diagram.
• ⊞ Tidy layout — arranges the sheet the way fluid-power drawings are arranged: energy flows up the page and the actuation sequence reads left to right. Power unit along the bottom, its pressure controls just above, directional valves in the middle, flow controls and checks above those, actuators along the top; one column per working circuit. Undoable, so try it and press Ctrl+Z if you prefer your own arrangement.
• ⊔ Repeat tank symbols — ISO 1219-2 explicitly permits drawing the reservoir symbol more than once, and this is the main reason professional diagrams look uncluttered. Long drain runs heading back to the power unit are replaced with a tank symbol placed right at the port that drains. Several tank symbols still mean one tank — the simulator treats them as one reservoir, so the oil temperature does not change because you drew the symbol three times.

How the pipes are routed: wires are routed by a cost-based search rather than a fixed shape, so they run only horizontally and vertically, keep clear of the symbols, never share a line with another wire, and cross as rarely as they can. Corners are expensive in that search, which is what keeps runs compact and stops the picture reshuffling when you nudge a component. Crossings are drawn plainly and a filled dot means the lines are joined — that dot, and only that dot, is what ISO 1219 uses to tell a junction from a crossover. Drag any wire segment to override the route by hand; your route is then kept as-is.

Valve shortcuts: E extends, R retracts and C centres every directional valve in the circuit at once — 4/3, 4/2, 5/2, 5/3, 3/2, 2/2 and their normally-open variants, and a proportional valve is driven to full command. Space starts and stops the run. (Rotation is Shift+R, so that R always means retract even when a component is selected.)

Zoom & Pan: Ctrl+Scroll to zoom towards cursor, Ctrl+Drag or H key for pan mode, pinch-to-zoom on touch. Toolbar buttons: Zoom In/Out, Pan Toggle, 1:1 Reset, Fit All. Right-click empty canvas toggles pan mode.

Fullscreen: Click the fullscreen button (bottom-right) to expand the canvas with the component palette.

Benchmarked against FESTO FluidSIM, the simulator ships with three industrial-grade panels below the canvas:

Circuit Diagnostics — a live design-and-safety checker that re-runs whenever you edit the circuit and on every simulation frame. It flags missing pumps, unconnected components, actuators with unwired ports, over-set pumps that waste energy, over-running loads with nothing holding them, and cases where the pump is running but flow is blocked. Two of the checks are written against ISO 4413 clause 5.4.5.1, which requires every hydraulic system to limit its pressure by a means that cannot be defeated: the simulator reports an error if there is no pressure-relief device at all, and a second error if a relief valve is present but can only be reached through a directional control valve. The second case is the one students get wrong — a relief hidden behind a closed-centre DCV protects nothing, because the moment the spool centres the pump is deadheaded with no path to tank. A coloured summary pill shows at a glance whether all checks pass (green), there are warnings (amber), or there are errors (red).

Fault Injection — inject real-world failure modes while the simulation runs: pump failure (total loss), external leak (50% pressure drop), blocked filter (flow restriction), oil overheating (viscosity drop, 30% flow loss), relief valve stuck closed (no pressure cap), cavitation (suction loss, 40% flow down), and air ingress (spongy response). Use the dropdown to pick a fault and the Status readout will switch to red with the fault name; click Clear fault to recover. Tip: tee a charged accumulator onto the pressure line before injecting pump failure and the status will switch to “Accumulator discharging — emergency supply” while the stored oil keeps the actuator moving — a realistic demonstration of emergency ride-through.

Oscilloscope & Data Logger — a four-channel scrolling scope. Assign any gauge, flow meter, cylinder, motor, or pump in the circuit to any of CH1–CH4 and watch live pressure, flow, extension, RPM, or temperature traces over a 10-second window. Each channel auto-scales independently. Use Pause to freeze the trace, Clear to reset the buffer, CSV to export the entire time-series for analysis in Excel/MATLAB, and PNG to save a watermarked screenshot for reports. This is the fastest way to capture step-response, stall, sequencing, or fault recovery behaviour for coursework and lab evidence.

Keyboard shortcuts: Space = Run/Stop, Ctrl+Z = Undo, Ctrl+Shift+Z = Redo, E/C/R = Set all DCVs to Extend/Center/Retract, Delete = Delete selected (annotation or component), D = Duplicate component, Escape = Exit pan mode / Cancel.

Zoom shortcuts: Ctrl+= Zoom in, Ctrl+- Zoom out, Ctrl+0 Reset zoom, Ctrl+1 Fit all, H Toggle pan mode.

• Always start with a Power Unit — every hydraulic circuit needs a pump.
• Add a Relief Valve early to protect against over-pressure.
• Use pre-built circuits to learn — load, study, modify, observe.
• Rotate components for compact, readable schematics.
• Right-click for options — Info, Duplicate, Rotate, Delete.
• Watch pressure readings during simulation — unexpected values indicate incorrect valve settings or missing return paths.
• Master Practice mode calculations before attempting the Quiz.

The simulator draws to ISO 1219-1, and the line style carries meaning:

• Solid line — a working line. Real oil flows along it, and the animated particles run on it.
• Dashed line — a control (pilot) line. It transmits a pressure signal and carries no working flow, so no particles run on it. Pilot ports are drawn as hollow violet dots.
• Fine dashed line — an external drain (port Y), returning spring-chamber leakage to tank.
• Dash-dot rectangle — several elements built into one housing, e.g. the throttle and check valve inside a one-way flow control, or the metering orifice and compensator spool inside a pressure-compensated flow control.

Port codes (ISO 1219-2): P pressure supply, T/T1/T2 tank return, A / B work ports, X remote pilot, Y external drain, M gauge tap. Hover any port for its description.

Directional valve envelopes. The port lines attach to the rest envelope — the one beside the return spring — and the spool block slides behind them; the envelope currently in circuit is highlighted in cyan. Inside each envelope the arrows are generated from the same routing table the solver uses, so what you see is what the physics does. A blocked port is a line ending in a perpendicular cap (⊥), never a cross: a cross means crossed flow paths, which is what a retract position looks like.

Centre conditions on a 4/3 valve — Closed: all four ports capped, the pump deadheads over the relief. Tandem: P joined to T along the bottom with A and B capped, so the pump unloads while the actuator is locked. Open: all four ports commoned. Float: A and B to tank, P capped — the actuator is free to be pushed.

External drains. The Sequence Valve and the Pressure Reducing Valve each carry a Y port. A real valve of either type cannot vent its spring chamber through an outlet that is under pressure, so ISO requires the drain; run it back to tank. The diagnostics panel will remind you if you leave it unconnected. The drain is optional in the simulator — it carries no working flow — but connecting it is what makes the schematic correct.

Every watt the pump delivers that does not leave as mechanical work at an actuator ends up as heat in the oil. Drop a Temp Gauge onto the circuit and you can watch it:

heat in = p·Q/600 at the pump − Σ(F·v) and Σ(T·ω) at the actuators, plus any Oil Heater

heat out = (k_tank + k_cooler) × (T_oil − T_ambient)

The reservoir sheds heat by natural convection at about 12 W/(m²·K) over the five exposed faces of the tank; an Oil Cooler at 100 % effectiveness adds another 0.5 kW/K. If you have not drawn a Reservoir the simulator sizes one at the usual three times the pump’s per-minute delivery.

Two things fall out of this that are worth seeing for yourself. First, a bare tank cannot shed much: 5 kW of throttling loss into a 100 L reservoir has no steady state below boiling, which is why real machines have coolers. Second, metering is expensive — a meter-in circuit burns the whole difference between pump pressure and load pressure at full flow, and the gauge shows exactly that. Compare a meter-in template against a pressure-compensated pump or a tandem-centre unloading circuit.

Oil temperature is time-compressed by 120× so a lesson can watch it happen: one second of simulation is two minutes of running. Real time constants are hours — a 100 L tank has a thermal capacity of about 165 kJ/K against roughly 0.013 kW/K of tank cooling. Mineral oil should be kept below 60 °C; oxidation roughly doubles for every 10 K above that, and the gauge marks the limit in red.