Come and find out more about what needs to be taken into account so as not to make a mistake when choosing a motor pump.
(Vilmar Rossi – FAMAC Engineering)
To correctly choose a pump or motor pump, some considerations or evaluations of the application must be made to know if we are dealing with a simple application of transferring clean water and without particles or a more aggressive liquid such as corrosive liquid, petroleum derivatives, food product or with solids and fibrous objects, for example.
In addition to respecting technical issues of equipment operation, selecting the correct product will ensure less “effort” from the hydraulic set (pump + hydraulic installation), better performance and, consequently, lower energy expenditure and lower maintenance costs. Best of all worlds, right?
Of course, choosing the right equipment is not the only guarantee of “zero defects”, but this process is a key part of minimizing problems in your pumping system, whatever it may be.
To better explain how we can do this, let's consider that we are dealing with a civil construction work, which could be:
- For the depletion of rainwater that accumulated in a work;
- To transfer water from the cistern on the ground floor of the building to the water tank on the other floors;
- For transferring sewage to sanitation pipes.;
- For pumping water from an artesian well to an elevated water tank;
- To pressurize water for irrigation of lawns, gardens or washing patios and sidewalks;
- For draining rainwater in case of flooding;
- For the operation of swimming pools and whirlpools;
- To ensure the required minimum pressure in apartments on the upper floors in a residential building; or
- To guarantee an ideal pressure for comfort in a private bath.
A centrifugal pump or motor pump normally adapts easily to all these situations and is therefore the most used when the objective is to transfer water or a low viscosity liquid from one place to another, as well as for pressurizing systems.
But let's take it easy: it's not just choosing any centrifugal model or relying on a single variable, like the power of the equipment (for example, by such CV, or horsepower), as many end up doing, without understanding what this represents.
So, to make everything well explained, let's make a summary of the basics that you will need to know, in case you don't know or are starting in the pumping segment. Follow here with us!
First, you need to know that the main units of measurement used in hydraulics are m³ / h (cubic meters per hour) and mca (meters of water column).
The unity m³ / h possibly it's an old acquaintance of yours, from your school days... It's a volume measurement unit that will be used here to establish the flow required or coming from the pumping system.
Yes, mca (meters of water column) is not that well known. To better understand this concept, let's take the simple example of a shower. Inside a bathroom in a house, for the electric shower to work, in addition to the electricity (of course!) it needs a minimum water pressure and for us to have that it is necessary for the shower to be at least 1,5 meters below the shower box. 'water. In the case of buildings over 40 meters high, the problem will be the high pressure, above what the equipment can withstand. So, for electric showers to work without installing additional items such as pressurizers or pressure reducers, the difference in height between the water tank and the shower must be between 1,5m and 40m, that is, present mca between 1,5 and 40.
Once the measurement units have been clarified, we proceed to analyze the aspects that will influence the proper selection of the pump or motor pump. Take a look:
water flow – It is the amount of liters of water that you want to transfer or make available in a piece of equipment in a given time. For example: 1 m³/h or 1.000 liters/h. When dealing with flow, we must not confuse volume with velocity, that is, if the objective is to transfer the largest possible volume of water, we must reduce the velocity of the water in the pipe (increasing the pipe diameter); if we want pressure in a sidewalk washing nozzle, for example, we must provide pressure so that the water velocity increases in the washing nozzle.
Repression – As discharge, consider the sum of the height and length of the pipe from the pump outlet to the final destination of the water. For dimensioning the discharge, we have few limitations, as there are pumps for any pressure and flow, being limited by acquisition costs, energy consumption and possible maintenance.
Suction – As suction, consider the sum of the height and the length of the piping from the water inlet in the pump to the fluid level in the water catchment reservoir. What can limit the suction capacity is not the size or the capacity of the pump, but a thermodynamic issue of the fluid, known as NPSH or cavitation. A practical tip is that when the water intake is more than 3 meters below the pump, always calculate the NPSH required by the installation and check the NPSH of the pump to ensure that the vapor pressure of the liquid is not reached.
Obs.: Since this is a more technical question, if you need to, you can consult one of the specialists here at FAMAC or make use of calculation and selection applications for pumps available on the market, such as our Sizer, available on the home page from the website.
Accessories – In a more accurate sizing, we must consider the hydraulic connections, foot valves, check valves, registers, curves and elbows, all components that contribute to the water reducing its speed, increasing the head losses and consequently increasing the pressure that the pump must make available to the application. If it is necessary to maintain the water flow defined in the project, it is necessary to count how many connections must be installed in the entire network and calculate the head losses for these accessories.
Piping and Fittings – With the above information in hand, it is necessary to determine the pipe gauge (in inches or millimeters) and the pipe material (iron or PVC). These two pieces of information will determine the head losses and consequently the pressure required to provide the determined water flow.
Thus, in summary, the process of selecting the model of pumps begins considering its application, be it clean water discharge, sewage, drainage, swimming pool or hydromassage, passage heaters, pressurization of points or equipment or any other application. .
Restrictions and specifications of the motor pump's own construction project must also be considered, since they aim at the best efficiency and the lowest manufacturing and maintenance cost for each application. For example, a booster pump for clean water will not satisfactorily meet the draining of rainwater or sewage, or even one designed to work out of liquid will not work properly when submerged.
The mathematical calculations involved in this process of choosing the best pump to install will be basically the same for most applications.
- If you are an expert on the subject or already work with pumps and motor pumps, you should already be familiar with such calculations. Now, if you're a newbie and don't even know where to start, here are two smart tips:
- Access “Downloads” here on the FAMAC website and download the booklet “Pumps and Motorpumps”. You will have access to a well-explained content about sizing motor pumps.
Make use of the FAMAC Sizer, a system that we have developed to help you in this process of choosing the right equipment for each type of situation.
Speaking of the sizer, next week here on the blog we will explain in more detail what you can do and how to best use it.
Did I hear a “VIVA”? So see you soon!
