Type: Tutorial Audience: Engineering students and trainees Goal: By the end of this tutorial, you will have started a simulated pump system, found the operating point, and observed how throttling a valve and changing system parameters shift that operating point — linking the simulation directly to real centrifugal pump behaviour.
This tutorial guides you through a structured hands-on session with the Pump Simulator at:
The simulator models a centrifugal pump (P1) delivering fluid through an isolation valve (V1), a control valve (V3), and back to a supply tank. It computes the operating point in real time — the flow rate and head at which the pump curve and the system curve intersect — and displays the result on live charts.
You will complete five steps:
No prior experience with the simulator is required. You should be comfortable with the concepts of flow rate, pressure, and what a centrifugal pump does. All concepts introduced in the steps are explained as you go.
Before starting, take a moment to orient yourself.
The SVG diagram shows the process circuit:
| Element | Symbol | What it represents |
|---|---|---|
| P1 | Circle with impeller | Centrifugal pump — click to start or stop |
| V1 | Butterfly symbol | Isolation valve — click to open or close |
| V3 | Angled valve symbol | Control valve — opening set by the V3 slider |
| FT | Flow transmitter tag | Displays current flow rate in L/s |
| PT suction | Pressure circle | Upstream pressure before the pump (bar) |
| PT discharge | Pressure circle | Downstream pressure after the pump (bar) |
| WT | Wattmeter tag | Displays shaft power in W |
| Tank | Rectangle with fill level | Supply/return tank — level shown as % |
When the pump is running and fluid is flowing, the pipes change colour and animated flow arrows appear. All displayed readings include 1.5% random measurement noise, simulating real instrument behaviour.
Two charts update in real time:
Three sliders let you change system conditions:
| Slider | Range | What it changes |
|---|---|---|
| V3 | 0–100 % | Control valve opening → adjusts system resistance |
| H_st | 0–50 m | Static head → adjusts the baseline of the system curve |
| P_max | 200–3000 W | Pump power rating → scales the pump curve via affinity laws |
A coloured indicator dot and text line below the diagram show the current system state: idle, running, or the reason flow is not occurring.
Set the sliders to these starting values before beginning:
| Control | Starting value |
|---|---|
| V3 opening | 5 % |
| H_st | 2.0 m |
| P_max | 1000 W |
These are the default values when the page loads, so no adjustment is necessary unless you have changed them.
Now start the system in this order:
If you click P1 before opening V1, the pump will appear to run but no flow will occur. Always open the isolation valve first — this is standard practice in real process plants to prevent pump dead-heading.
What you should see:
The faint fluid sound from your browser's audio output confirms the system is live. (Sound requires the page to have received a user interaction first — clicking the pump satisfies this requirement.)
With the system running at V3 = 5%, H_st = 2.0 m, P_max = 1000 W, read the following values from the diagram:
| Variable | Where to read it | Approximate value |
|---|---|---|
| Flow rate Q | FT tag on diagram | ~0.3 L/s |
| Discharge head H | H-Q chart — operating point dot | ~55 m |
| Efficiency η | Efficiency chart — operating point dot | ~15–20 % |
| Shaft power W | WT tag on diagram | ~80–120 W |
| Suction pressure | PT suction tag | ~–0.2 bar (slight vacuum) |
| Discharge pressure | PT discharge tag | ~5 bar |
| Tank level | Tank fill indicator | ~65 % |
All readings fluctuate slightly due to the simulated measurement noise. This is intentional — real instruments never produce perfectly steady readings.
The efficiency curve has a peak — the Best Efficiency Point (BEP) — at approximately 60% of the maximum flow rate. At V3 = 5%, the valve is nearly closed and flow is far below BEP. This is called off-design operation. Running a centrifugal pump far from BEP for extended periods causes increased bearing loads, vibration, and heat — something real process engineers actively avoid.
The H-Q chart shows the system curve passing through the origin (or near-origin for low static head) and rising steeply because the nearly-closed V3 creates high resistance. The operating point is where this system curve crosses the pump curve.
Now gradually open V3 and observe how the operating point moves.
Move the V3 slider in steps and read the values at each position:
| V3 opening | Expected Q (L/s) | Expected H (m) | Expected efficiency (%) |
|---|---|---|---|
| 5 % | ~0.3 | ~55 | ~15–20 |
| 25 % | ~0.6 | ~48 | ~35–45 |
| 50 % | ~0.85 | ~40 | ~55–65 |
| 75 % | ~1.0 | ~32 | ~65–70 |
| 100 % | ~1.1 | ~25 | ~68–72 |
Opening V3 reduces the system resistance — the R term in the system curve equation H_sys = H_static + R × Q². As R decreases, the system curve becomes flatter. A flatter system curve intersects the pump curve at a higher flow rate and lower head. This is why:
At V3 = 100%, the system is at its least resistive state (for the current H_st setting) and the pump operates near or above BEP — the most efficient point.
In real plants, control valves are throttled to regulate flow to a downstream process. Closing the valve reduces flow to the required rate but moves the pump away from BEP. Energy-efficient design uses variable-speed drives (VSD) instead — reducing pump speed rather than throttling — but this simulator uses a fixed-speed pump to isolate the valve-throttling effect.
Return V3 to 50% so you have a clear mid-range operating point to compare against.
Now move the H_st slider from its current value (2.0 m) upward to 20 m, then to 40 m.
| H_st (m) | Effect on system curve | Effect on Q | Effect on H |
|---|---|---|---|
| 2 m | Low baseline → curve starts near origin | Higher Q | Lower H |
| 20 m | Moderate baseline → curve elevated | Moderate Q | Moderate H |
| 40 m | High baseline → curve very elevated | Lower Q | Higher H |
Static head (H_st) is the pressure the pump must overcome simply due to elevation difference and back-pressure — before any friction losses. It is the "baseline" of the system curve. A pump delivering fluid to a high-elevation tank faces a high static head regardless of flow rate.
When you raise H_st to 40 m, the system curve is shifted up and to the left. The intersection with the pump curve moves to a lower flow rate. If you raise H_st high enough, the system curve no longer intersects the pump curve at all — the pump cannot overcome the static head and no flow occurs.
Reset H_st to 2.0 m before continuing to Step 5.
With V3 = 50%, H_st = 2.0 m, now move the P_max slider from 1000 W up to 2000 W, then try 500 W.
| P_max (W) | Effect |
|---|---|
| 500 W | Smaller pump — pump curve shifts down and left; lower Q and H |
| 1000 W | Reference pump — baseline |
| 2000 W | Larger pump — pump curve shifts up and right; higher Q and H |
The simulator scales the manufacturer pump curve using the pump affinity laws (similarity laws). For a geometrically similar pump at a different speed or impeller size:
By adjusting P_max, you are simulating either a larger or smaller pump of the same family. A 2000 W pump produces more head and more flow at every point on its curve compared to a 1000 W pump of the same design. This is why larger process systems require larger pump selections.
The operating point moves to a higher flow rate and higher head as P_max increases — because the pump curve has been scaled up while the system curve (set by V3 and H_st) remains the same.
By completing this tutorial, you have directly observed the following engineering fundamentals:
| What you did | What it demonstrates |
|---|---|
| Opened V1 before starting P1 | Isolation valve sequencing; dead-heading risk |
| Read Q, H, η, power at low V3 | Off-design operation; poor efficiency at low flow |
| Opened V3 progressively | Throttling reduces resistance; operating point moves along pump curve toward BEP |
| Increased H_st | Static head elevates the system curve; pump delivers less flow against more back-pressure |
| Changed P_max | Pump affinity laws; larger pumps shift the entire pump curve outward |
The central concept linking all five steps is the operating point — the intersection of the pump curve and the system curve. In real process engineering, selecting, sizing, and operating centrifugal pumps is fundamentally about controlling where that intersection sits under all operating conditions (normal, minimum flow, maximum flow, startup, shutdown).
A centrifugal pump is a rotodynamic machine that converts rotational kinetic energy (from a motor and impeller) into fluid energy — increasing both the velocity and pressure of the fluid. It is the most common pump type in process industry.
The pump delivers flow by centrifugal force: fluid enters axially at the impeller eye, is accelerated outward by the rotating vanes, and exits at higher pressure through the volute casing. Flow rate decreases as the outlet resistance (back-pressure or head) increases.
The pump curve (also called the head-flow curve or H-Q curve) describes the relationship between flow rate (Q) and developed head (H) for a given pump at a fixed rotational speed and impeller diameter. It is the fundamental performance characteristic of a centrifugal pump.
Typical behaviour:
The pump curve is supplied by the pump manufacturer, determined from physical test data, and reproduced on a characteristic curve chart.
The system curve describes the total head that the piping system requires the pump to provide at each flow rate. It has the general form:
H_sys = H_static + R × Q²
Where:
H_static — static head: elevation difference plus any fixed back-pressure (does not depend on flow)R × Q² — dynamic (friction) head: head loss due to pipe friction, fittings, and valve resistance, which increases with the square of the flow rateR — system resistance coefficient (influenced by pipe size, length, fittings, and control valve opening)The system curve is not a pump property — it is a property of the piping circuit the pump is connected to.
The operating point is the intersection of the pump curve and the system curve on the H-Q chart. It is the unique combination of flow rate and head at which the pump and system are in equilibrium — the head the pump produces exactly equals the head the system requires at that flow rate.
The operating point is not fixed. It moves whenever:
A process engineer's job is to ensure the operating point remains within the pump's acceptable operating range under all process conditions.
The Best Efficiency Point (BEP) is the flow rate at which the pump operates at its highest hydraulic efficiency. At BEP, energy losses inside the pump (recirculation, turbulence, mechanical friction) are minimised.
Running a pump far from BEP — either at very low flow or very high flow — causes:
Good pump selection places the expected operating point at or near BEP.
Head (H) is a measure of energy per unit weight of fluid, expressed in metres of fluid column (m). It is equivalent to pressure divided by the product of fluid density and gravitational acceleration:
H = ΔP / (ρ × g)
Using metres of head (rather than pressure in bar or Pa) is convenient because it is independent of fluid density for the purpose of pump curve plotting. A pump that develops 40 m of head does so regardless of whether it is pumping water or a heavier fluid — but the resulting pressure difference in bar will be different.
Static head (H_st) is the component of total head that does not depend on flow rate. It includes:
Even when no fluid is moving, the pump must overcome the static head before any flow can start. If the pump's shut-off head is less than the static head, no flow will occur regardless of how much the valve is opened.
Friction head is the head lost to fluid friction in pipes, fittings, and valves. It increases approximately with the square of the flow velocity (and therefore the square of the flow rate). At zero flow, friction head is zero. As flow increases, friction head increases rapidly.
The resistance coefficient R in the system curve equation captures this behaviour. A small pipe, long run, or partially closed valve all increase R and steepen the system curve.
A control valve is a variable-resistance device that adjusts the system resistance to regulate flow. In the simulator, V3 represents a throttling valve. At low opening, V3 presents high resistance (steep system curve → low flow). At full opening, V3 presents low resistance (flat system curve → high flow).
The relationship between valve opening (%) and flow is non-linear, governed by the valve's flow characteristic (linear, equal percentage, or quick opening).
An isolation valve (V1 in the simulator) is an on/off device — either fully open or fully closed. It is not used for flow regulation. Its purpose is to isolate equipment for maintenance or to prevent unintended flow. Opening an isolation valve downstream of a stopped pump before starting it is standard operational practice.
The pump affinity laws (or similarity laws) describe how pump performance scales with changes in rotational speed (N) or impeller diameter (D):
| Variable | Relationship |
|---|---|
| Flow rate Q | Q ∝ N (or D) |
| Head H | H ∝ N² (or D²) |
| Power P | P ∝ N³ (or D³) |
If pump speed doubles, flow rate doubles, head quadruples, and power increases eightfold. These laws allow engineers to predict the performance of a pump at a different speed without re-testing, and to understand variable-speed drive (VSD) energy savings.
In the simulator, the P_max slider scales the pump curve using an approximation of the affinity laws — a larger power setting represents a larger (or faster) pump of the same design family.
Hydraulic power (P_hydraulic) is the useful power delivered to the fluid:
P_hydraulic = ρ × g × Q × H
Shaft power (P_shaft) is the total power drawn by the pump motor from the electrical supply. It is always greater than hydraulic power due to mechanical and hydraulic losses inside the pump.
Pump efficiency (η) is their ratio:
η = P_hydraulic / P_shaft
The simulator's WT instrument shows shaft power. Efficiency is shown on the efficiency chart.
Real process instruments never produce perfectly steady readings — they include measurement noise from electrical interference, sensor limitations, turbulence effects, and transmitter resolution. The simulator adds ±1.5% random noise to all displayed readings at each refresh cycle (every 350 ms) to replicate this behaviour. The underlying calculated values are exact; only the displayed values fluctuate.
Cavitation occurs when the pressure at the pump inlet (suction) falls below the vapour pressure of the fluid. Vapour bubbles form in the low-pressure region, then collapse violently as they enter the higher-pressure zone inside the impeller. This causes pitting damage to impeller surfaces, vibration, noise, and loss of head.
Cavitation risk increases when:
The simulator does not model cavitation, but the suction pressure gauge (PT suction) shows the slight vacuum on the suction side when the pump is running — a real indicator of suction conditions.
Flow Rate Calculator — Calculate the volumetric or mass flow rate through a pipe for any liquid or gas. Useful for verifying the flow conditions observed in the pump simulator.
Restriction Orifice Calculator — Find Flow Rate — Calculate the flow rate through a fixed restriction at a known differential pressure. Complements the pump simulator by quantifying flow through control valve restrictions.
Restriction Orifice Calculator — Find Pressure Drop — Calculate the pressure drop across a fixed bore at a given flow rate. Use this alongside the pump simulator to understand valve pressure drop at specific operating points.
Restriction Orifice Calculator — Find Size — Size a restriction orifice for a target flow rate and pressure drop.
Orifice Plate Calculator — Find Flow Rate — Metering orifice plate flow calculation per ISO 5167. Relevant for measuring pump flow in process systems.
Orifice Plate Calculator — Find Pressure Drop — Calculate the differential pressure generated by a metering orifice plate at a given flow rate.
Density of Common Liquids — Reference density values for water and other process liquids. Required for converting between volumetric flow (L/s, m³/h) and mass flow (kg/h).
Absolute Viscosity of Common Gases — Dynamic viscosity reference for gas-phase calculations.
Molecular Weight of Common Fluids — Molecular weight data for gas density calculations.
Introduction to Instrumentation — Foundational article on measurement and control principles in process plants. Provides context for the instruments shown in the pump simulator diagram.
Pressure Measurement — Explains pressure sensing principles relevant to the suction and discharge pressure gauges in the simulator.
Temperature Measurement — Overview of temperature sensing in process systems.
Instrument Selection Principles — Guidance on selecting measurement instruments for process applications, including the types used in pump monitoring.
Q1 Why does closing V3 reduce the flow rate if the pump is still running at full power?
A1 A centrifugal pump does not deliver a fixed flow rate regardless of conditions — its output depends on the resistance it faces. When V3 is nearly closed, the system resistance is very high. The pump must produce a large head to push even a small amount of fluid through the restriction. The operating point (intersection of pump and system curves) moves to the left on the H-Q chart: low flow, high head. The pump is still running and consuming power, but most of that power is going into pressurising the fluid against the closed valve rather than moving it.
Q2 What happens if I start the pump with V1 closed?
A2 If V1 (the isolation valve) is closed, the pump runs but no fluid circulates. This is called dead-heading. In the simulator, the status bar will show no flow and the operating point will appear at zero flow on the pump curve (shut-off head). In a real centrifugal pump, dead-heading causes the fluid inside the casing to heat up rapidly (from energy input without fluid movement), which can damage seals, cause cavitation, and degrade the impeller. Always open the isolation valve before starting the pump.
Q3 Why does efficiency matter and why is it low when V3 is nearly closed?
A3 Efficiency represents how much of the electrical power drawn by the pump motor is actually transferred usefully to the fluid. The remainder is lost as heat inside the pump — from internal recirculation, turbulence, bearing friction, and flow separation on the impeller vanes. At very low flow (V3 nearly closed), the fluid circulates internally rather than passing through the pump, causing high turbulence losses. Efficiency peaks at the Best Efficiency Point (BEP), typically around 60–70% of the maximum flow rate. Operating far from BEP wastes energy and accelerates pump wear.
Q4 What does changing P_max actually simulate?
A4 The P_max slider scales the pump curve using an approximation of the pump affinity laws. Increasing P_max simulates selecting a larger pump of the same design family — one with a bigger impeller or running at a higher speed. The entire pump curve shifts outward: higher head at every flow rate, and higher maximum flow. Decreasing P_max simulates a smaller or slower pump. In real engineering, pump selection involves choosing from a manufacturer's range of pump sizes and comparing their curves against the system curve.
Q5 What does "Trial A" in the header mean?
A5 The simulator is labelled "Trial A" to indicate it is the first in a planned series of simulation scenarios. Future trials may introduce additional complexity such as parallel pumps, series pumps, variable-speed drives, or more complex piping networks. Trial A establishes the baseline: a single fixed-speed pump, a single control valve, and a simple recirculating system.
Q6 Why do the readings fluctuate even when I am not touching anything?
A6 The simulator adds ±1.5% random noise to all displayed readings at each update cycle (every 350 ms). This behaviour is intentional — it replicates real process instrumentation, where signal noise from electrical interference, turbulence, and transmitter quantisation causes readings to oscillate slightly around their true value. A real control room operator learns to read the average value from a fluctuating display, not a single instantaneous reading. This is an important skill the simulator reinforces.
Q7 The pump is running and V1 is open but I still see zero flow. What is wrong?
A7 Check the V3 slider. If V3 is set to 0%, the control valve is fully closed and no flow can pass. Open V3 to at least 1–5% to allow flow to begin. Also verify that H_st is not set so high that the pump shut-off head is lower than the static head — in that case, the pump cannot overcome the system back-pressure and no flow occurs even with the valve fully open.
Q8 Is the fluid in the simulator water? Can I change the fluid?
A8 The simulator uses water as the process fluid at standard conditions (density 1000 kg/m³, g = 9.81 m/s²). The fluid type cannot be changed in the current version. For calculations involving other fluids (different densities or viscosities), use the dedicated calculators: the Flow Rate Calculator for volumetric flow, or the Restriction Orifice Calculator for flow through restrictions.