WHAT IS A WATER PUMP?
A water pump is an electrical machine designed to convert electrical power into energy, which is then used to displace and move water. The energy generated by the pump facilitates the movement of water from one location to another.
All water pumps consist of two essential components: an electric motor and a hydraulic section. The motor generates the power needed to operate the pump, while the hydraulic section is responsible for facilitating the water flow. Additionally, a sturdy support is utilized to securely mount the pump to its base, ensuring stability and preventing any unwanted movement.
STEP 1: FLOW
At home, everyone needs water
The maximum theoretical requirement is given by the sum of the quantities of water delivered to the various outlets of a flat multiplied by the number of flats. In practice, it is common practice that just some outlets are used simultaneously: that's why this number must be multiplied to a contemporaneity factor
1 - Dishwasher
2 - Toilet flushing
3 - Shower
4 - Washing machine
5 - Kitchen sink
6 - Garden watering
HOW TO CALCULATE YOUR PUMP'S FLOW RATE
Residential buildings consumption
Apartments with two toilets
Apartments with one toilet
It shows values of actual delivery, which depend on the number of flats connected to the water-supply system. Seven outlets are hypothesized for one-bathroom flats and ten outlets for two-bathroom flats.
Method 1
Method 2
Maximum consumption at points of demand
• In theory, the water maximum requirement derives from the sum of the litres per minute delivered to the various outlets of a flat multiplied by the n. of flats.
• In practice, just some of the outlets are used simultaneously: that's why we can consider normally 1/3 of the total requirement.
Outlet
Qu. delivered (l/min)
Sink
Wash-basin
Bath-whirlpool tub
10
10
18
Shower
WC-flush-tank type
WC-fast-feed type
12
7
90
Bidet
Washing machine
Kitchen sink
6
12
12
Dishwasher
Outlet w/ 1/2" tap
Outlet w/ 3/4" tap
8
20
25
Other buildings consumption
These buildings require quantities of water greater than those needed in residential buildings. The values are based on hypothetical numbers of persons present in these buildings. These values offer a guideline and may vary in accordance with particular requirements of projects.
Number of persons present in building
A Offices B Shopping centres C Hospitals D Hotels
STEP 2: HEAD
1) Static head:
Distance between the suction fluid surface and the maximum discharge elevation (highest outlet).
Example
1 - Total static head
2 - Static discharge head
3 - Static suction head
1 - Static discharge head
2 - Total static head
3 - Static suction lift
2) Friction:
(sum of the head losses in pipes)
By approximation, head losses may be quantified as follows:
• 0.5 m per floor in new systems,
• 1 m per floor in old systems.
Friction is flow rate dependent :
• x2 flow rate, x4 head loss
• ½ flow rate, ¼ head loss
Head loss can also be calculated for pipes:
By matching the flow rate and the delivery pipe diameter, in the chart below, you’ll find the head loss in a 100 m long pipe. For example, supposing you have Q=42 m3/h and delivery pipe Ø DN80.
Therefore, the head loss will be 7,5 meters.
If the pipe were 70 m long, the head loss in the system would be calculated as the following: 7,5 meters x 70 meters / 100 meters = 5,25 meters
Head loss In m for steel pipes
Q Flow
HL Head loss, m per 100 m
V = Flow velocity: max 1,5 m/s for suction
and 3 m/s for delivery
Head loss calculated on bends and valves
Head loss in cm for bends, gate valves, foot valves and check valves
1 - Water flow velocity
2 - Elbows
3 - Sweep elbow
4 - Gate valves
5 - Foot valves
6 - Check valves
System curve:
Static head + friction head = total head
1 - Friction Head
2 - Static head
3 - Operating point
Calculation example:
Parameters:
• (Flow) Q = 42 m3/h
• (Static head) Hg= 40 m
• 70m DN80 pipe
Calculation of friction:
70 m Ø 80 pipe= 5,25 m
+ 15 m of minimum residual pressure at the highest outlet for appliances
20,25m
1 - Foot valve
2 - Length
3 - Pipe
4 - Total Head =
40m + 20,25m = 61.55 m
STEP 3: PUMP
The golden rule is to choose a pump at the BEP!
Ideal selection zone
1 - High temp. rise
2 - Low bearing/seal life
3 - Reduced Motor Efficiency
4 - Low bearing/seal life
5 - Cavitation/high temp.Rise
1) Throttle control:
In case of a selection at the far right-end of the curve, the flow rate is easy to control and can be reduced through a valve at outflow:
this will assure the correct pump operating condition.
1 - Head
2 - Flow rate
3 - Pump curve
4 - Throttled curve
5 - System curve
2) Variable Speed Control / Inverter:
Constant pressure at different flows
STEP 4: NPSH
Pay attention to the suction capability of the pump, the “Net Positive Suction Head” required (NPSHr).
Its value is obtained in accordance with the flow
Vapour
pressure values
NPSH available
NPSH required
Check the following simplified formula for free-cavitation condition:
Where:
Hb = Atmospheric pressure (10 m)
h = Suction lift
Hf = Friction loss in the suction pipe (m)
Hv = Vapour pressure of the liquid (m);
Hs = Safety factor (about 0.5 m)
Diagram of manometric suction head with water up to 100 °C
Water Temperature in degrees Celsius
Manometric suction lift
(mwc)
Positive suction head (mwc)
1 - Practical curve
2 - Theoretical curse
Cavitation
As the liquid travels through the pump the pressure drops and if it is sufficiently low (below vapor pressure) the liquid will vaporize and produce small bubbles: these bubbles will be rapidly collapse due to the pressure created by the fast moving impeller vane
Rotation of Impeller
Collapsing bubbles
Vapor bubbles
Along with the noise, the shock of the imploding bubbles on the surface of the vane produces a gradual erosion and pitting, thus resulting in the pump damaging
It is often possible to adjust the flow via a gate valve on the delivery side, which will decrease the NPSHr (which is flow dependent) and restore the correct pump operating conditions.
Problems at the pump
Faults
Possible causes
Jammed pump
This may happen after periods of inactivity due to inner
oxidation.
To release smaller sized monobloc electro pumps use
a screwdriver at the notch on the back part of the shaft.
For the larger sizes, turn on the shaft or the flexible coupling.
Pumps which do not prime
Pump and/or suction pipe with air entrapped. Uncompleted priming or totally unprimed. Possible air entering from taps, drain or fill plugs, joints or stuffing box. Foot valve not fully immersed in the fluid or obstructed by deposits. Suction lift too high compared with the capability of the pump.Wrong direction of rotation.Wrong number of revolutions.
Insufficient flow
Piping and accessories of too small a diameter which cause too high head loss. Jammed impeller with presence of debris in the vanes.
Corroded or broken impeller. Impeller wear rings and/or pump casing worn by abrasion. Gas presence in the water, or too high fluid viscosity in case of fluids different from water.
Noise and vibrations in the pump
Unbalanced rotary part or worn ball bearings.
Pump and piping not
properly secured.
Too low flow rate for the selected pump.
Operation with cavitation
Overloaded motor
Pump characteristics higher than those of the plant
Fixed and rotary parts in contact tending to seize owing to a lack of lubrication. Too high rotation speed.
Wrong mains supply
Poor unit alignment
Fluid with too higher density than the design
STEP 5: DRIVING DEVICES
Automatic working pressure systems, ready for the installation.
Composed by pump, pre-rated and adjustable pressure switch, pressure gauge, connector, membrane tank and cable with plug.
SUPERDOMUS
HIDROMATIC - HIDROTANK
Electronic flow control devices
Start and stop the pump in accordance with the opening and closing of the taps
Variable speed drives / Inverters: EPIC & IPFC
Maximum efficiency coupled with minimum energy consumption:
control pump operation for constant pressure at different working conditions.
EPIC
For domestic systems with single phase supply
a) EPIC provided with the pump (wall kit available)
b) PUMPSET + EPIC provided with the pump (wall kit available) + a tank + a gauge and a connector with a non-return valve
IPFC
For residential, commercial or industrial use for more powerful pumps
ULTRA + IPFC with the pump (wall kit available)
ULTRA + VDS BOOSTERSET
Constant pressure booster-set with 2 / 3 / 4 / 5 pumps controlled by EPIC / IPFC.
Glossary of water pump terms
Flow
Pump capacity refers to the measurement of how much liquid a pump can handle within a specific time frame. This capacity is typically expressed in liters per minute (L/min), liters per second (L/sec), or cubic meters per hour (m³/hr).
Head
In fluid mechanics, "head" is a term used to describe the energy stored within a fluid as a result of the pressure applied to its container. It is measured as the vertical height of the fluid column, where a standard unit of 10 meters is equivalent to one atmosphere or 14.7 pounds per square inch (psi).
Pressure
Back-pressure refers to the resistance encountered by a pump on its discharge side due to factors such as the height of the fluid column (head) or any other constriction in the system.
Friction Loss Head
The head generated by friction of moving liquid, against the walls of the discharge pipes.
NPSH (Net Positive Suction Head)
The energy needed to ensure the entry of liquid into the pump volute, sourced from external factors such as static head or atmospheric pressure.
Cavitation
Cavitation happens when there is inadequate Net Positive Suction Head (NPSH), resulting in excessively low suction pressure that triggers cavitation. This phenomenon leads to erosion on the metal surfaces as vapor bubbles collapse, causing the liquid to rapidly rush into the surrounding areas. This sudden rush creates a water hammer effect.
Performance Curve
The graph illustrates the relationship between the total head and flow rate for a particular pump, featuring a specific impeller and its unique set of characteristics.
Pipe Friction Loss
Head loss occurs as a result of the friction between the process fluid and the pipe walls and joints.
B.E.P. (Best Efficiency Point)
The conversion of kinetic energy into pressure energy by a pump is not achieved with 100% efficiency. Losses occur due to factors such as friction in seals and bearings, as well as friction of the pumped fluid over the impeller. The Best Efficiency Point (BEP) represents the volumetric flow rate at which the pump is designed to maximize the conversion of kinetic energy into pressure energy.