Aim of the Experiment
- To determine the performance characteristics (Head vs Discharge, Q vs Efficiency) of centrifugal pumps operating individually, in series, and in parallel
- To compare the effect of series and parallel configurations on total head and flow rate
Theory
When pumps are connected in series or parallel, the combined performance differs from that of a single pump:
Pumps in Series
The total head increases while the flow rate stays the same as a single pump. The combined H-Q curve is obtained by adding the head values of each pump at the same flow rate:
Hseries = H₁ + H₂ (at same Q)
Series configuration is used when high head is required at moderate flow — e.g., booster pumps in tall buildings.
Pumps in Parallel
The total flow rate increases while the head stays the same. The combined Q-H curve is obtained by adding flow rates at the same head:
Qparallel = Q₁ + Q₂ (at same H)
Parallel configuration is used when high flow rate is required at the same head — e.g., water distribution networks.
Apparatus
- Multi-pump test rig (FluidoSurge-X-192) with two identical centrifugal pumps
- Manifold piping system with valves for series/parallel switching
- Pressure gauges at pump inlet and outlet
- Flow meter (rotameter or electromagnetic)
- Wattmeter or power analyser for shaft power measurement
- Control valve on delivery line for varying flow resistance
Procedure
Single Pump Characteristics
- Configure the valve arrangement for single pump operation. Keep Pump 1 running; isolate Pump 2.
- Fully open the delivery valve. Record flow rate (Q), inlet pressure (Pi), outlet pressure (Po), and power input (Pw).
- Gradually close the delivery valve in steps to reduce flow rate. At each step, record Q, Pi, Po, and Pw.
- Continue until the delivery valve is fully closed (shut-off head condition, Q = 0).
- Calculate head at each point: H = (Po − Pi) / ρg + velocity head difference.
Pumps in Series
- Reconfigure the valve manifold to connect both pumps in series (outlet of Pump 1 feeds inlet of Pump 2).
- Start both pumps. Repeat the same procedure — vary delivery valve position and record readings at 6–8 flow rates.
Pumps in Parallel
- Reconfigure the valve manifold for parallel connection (both pump outlets join a common delivery header).
- Start both pumps. Record Q, pressure, and power at each delivery valve position as before.
Observation Table
| Config | Q (L/min) | Pi (bar) | Po (bar) | H (m) | Pw (W) | η (%) |
|---|---|---|---|---|---|---|
| Single | ||||||
| Series | ||||||
| Parallel | ||||||
Calculations
Total Head: H = (Po − Pi) × 10 / ρg (m of water, when pressures in bar)
Hydraulic Power Output: Ph = ρgQH (W)
Overall Efficiency: η = Ph / Pw × 100%
Graph
Plot three H-Q curves on the same graph (Single, Series, Parallel). Observations:
- Series curve: same shape as single pump curve but shifted vertically upward (doubled head at each Q)
- Parallel curve: same shape but shifted horizontally to the right (doubled Q at each H)
Precautions
- Never run centrifugal pumps dry — ensure the system is primed before starting.
- Open the delivery valve before starting pumps in series to avoid pressure build-up.
- Change flow rates slowly and allow the system to stabilise before recording readings.
- Check that both pumps rotate in the correct direction.
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