Two identical pumps, each capable of delivering 0.2 cumec, against a head of 30 m, are connected in parallel. The resulting discharge will be
0.4 cumec against a head of 30 m
Understanding Pumps in Parallel Connection
This question asks about the combined performance of two identical pumps connected in parallel. When pumps are connected in parallel, their main purpose is typically to increase the total discharge (flow rate) for a given head (pressure difference).
Let's consider the characteristics of the individual pumps and how they behave when connected in parallel.
Analyzing Individual Pump Performance
Each identical pump has the following specified performance:
- Discharge (\(Q\)) = 0.2 cumec
- Head (\(H\)) = 30 m
This means that at a head of 30 meters, a single pump can deliver a flow rate of 0.2 cubic meters per second.
Combined Performance of Pumps in Parallel
When two identical pumps are connected in parallel, they draw water from a common suction pipe and discharge into a common delivery pipe. In this configuration, the total head developed by the system is ideally the same as the head developed by each individual pump at the operating point. The total discharge, however, is the sum of the discharges of the individual pumps at that common head.
Assuming the system requires a head of 30 m (the head against which the pumps are rated), each pump will contribute its rated discharge at this head.
Calculating Total Discharge and Head in Parallel
Given two identical pumps connected in parallel:
- Total Head: The head remains the same as the individual pump head at the operating point. Since the pumps are rated to deliver 0.2 cumec against a head of 30 m, the combined system operating against a head of 30 m will also have a head of 30 m.
- Total Discharge: The total discharge is the sum of the discharges of the individual pumps.
Total Discharge (\(Q_{total}\)) = Discharge of Pump 1 (\(Q_1\)) + Discharge of Pump 2 (\(Q_2\))
Since the pumps are identical and operating against the same head (30 m), their individual discharges will be their rated discharge at that head.
\(Q_{total} = 0.2 \, \text{cumec} + 0.2 \, \text{cumec}\)
\(Q_{total} = 0.4 \, \text{cumec}\)
So, the resulting performance of the two identical pumps connected in parallel, operating against a head of 30 m, is a total discharge of 0.4 cumec at a head of 30 m.
Comparing with Options
Let's compare our calculated result with the given options:
- Option 1: 0.4 cumec against a head of 30 m
- Option 2: 0.4 cumec against a head of 60 m
- Option 3: 0.2 cumec against a head of 30 m
- Option 4: 0.2 cumec against a head of 60 m
Our calculated result of 0.4 cumec total discharge against a head of 30 m matches Option 1.
Summary of Parallel Pump Connection
| Parameter | Individual Pump | Two Identical Pumps in Parallel |
|---|---|---|
| Discharge (at 30m head) | 0.2 cumec | 0.2 cumec + 0.2 cumec = 0.4 cumec |
| Head (at stated discharge) | 30 m | 30 m |
Revision Table: Pump Connections
| Connection Type | Effect on Total Discharge | Effect on Total Head | Typical Application |
|---|---|---|---|
| Parallel | Discharge adds up (\(Q_{total} = Q_1 + Q_2\)) | Head remains approximately same as individual pump head (at the operating point) | Increasing flow rate for a relatively constant head system |
| Series | Discharge remains same as individual pump discharge | Head adds up (\(H_{total} = H_1 + H_2\)) | Increasing head for a relatively constant flow rate system |
Additional Information: Pump System Curves
It's important to note that the actual operating point of a pump or pump system is determined by the intersection of the pump characteristic curve (or the combined pump curve) and the system head curve. The system head curve represents the head required by the piping system for different flow rates (accounting for static lift and friction losses).
- For parallel pumps, the combined pump curve is obtained by adding the discharges of the individual pumps at the same head.
- The intersection of this combined curve with the system head curve gives the actual total discharge and operating head of the parallel pump system.
- In this specific question, we are given the performance "against a head of 30 m," which implies we are considering the capacity specifically at that head value, simplifying the calculation to the sum of individual discharges at that head.
Important Questions from Pumps
In a centrifugal pump, the flow enters the chamber along the axis of the chamber and is discharged:
The specific speed of a centrifugal pump is defined as the speed of geometrically similar pump which would -
Which of the following is a positive displacement pump?
Reciprocating pumps:
In the pumps that are used for water supply, generally the vertical distance between the centre line of a pump and the point of free discharge is known as
