Maximum performance
The maximum volume of water that the device can pump in a certain amount of time. It is one of the key specs of any pump because characterizes the volume of water with which the device can work. At the same time, it does not always make sense to pursue maximum performance — after all, it significantly affects the dimensions and weight of the unit.
Some formulas allow you to derive optimal performance values for different situations. So, if the pump is designed to supply water to water intake points, its minimum required performance should not be lower than the highest total flow rate; if desired, a margin of 20-30% can be added to this value. And for sewer models (see "Suitable for"), everything will depend on the volume of wastewater. More detailed recommendations for choosing a pump depending on performance can be found in special sources.
Maximum head
The maximum head generated by the pump. This parameter is most often indicated in meters, by the height of the water column that the unit can create — in other words, by the height to which it can supply water. You can estimate the pressure created by the pump using a simple formula: every 10 m of head corresponds to a pressure of 1 bar.
It is worth choosing a pump according to this parameter, taking into account the height to which it should supply water, as well as adjusting for losses and the need for pressure in the water supply. To do this, it is necessary to determine the difference in height between the water level and the highest point of water intake, add another 10 to 30 m to this figure (depending on the pressure that needs to be obtained in the water supply), and multiply the result by 1.1 — this will be the minimum pressure required.
Max. pressure
The highest pressure that the pump is capable of creating during operation. This parameter is directly related to the maximum head (see above); however, it is less obvious, and therefore, it is indicated rarely.
Pump type
The basic principle by which the suction action of the pump is carried out.
— Centrifugal. As the name suggests, this type of pump uses centrifugal force. Their main element is the impeller installed in a round casing; the inlet is located on the axis of rotation of this wheel. During operation, due to the centrifugal force that occurs during the rotation of the wheel, the liquid is thrown from the centre to its edges and then enters the outlet pipe directed tangentially to the circle of rotation of the wheel. Centrifugal pumps are quite simple in design and inexpensive, while they are reliable and economical (due to high efficiency), have a large suction height (see below), and the fluid flow is continuous. At the same time, the performance of such units can drop dramatically with high resistance in the water supply system. In addition, if the liquid level is below the inlet, the pump will have to be refilled with water before each start.
— Vortex. Peripheral pumps are somewhat similar to centrifugal pumps: they also have a round casing and an impeller with blades. However, in such units, both the inlet and outlet pipes are directed tangentially to the impeller, and the blades differ in design. The method of operation is also fundamentally different — by the name, of it uses the vortices formed on the wheel blades. Vortex units are significantly superior to centrifugal ones in terms of pressure; in addition, they are usually self-priming (see "Suction...type"), and the design in most cases is such that the pump has to be filled with water only when it is first turned on after installation. On the other hand, such models are sensitive to contamination — even small particles entering the impeller can cause damage, significantly reducing efficiency. Yes, and the efficiency of vortex pumps is low — 2-3 times lower than that of centrifugal pumps; they are also inferior in suction height (see below).
— Centrifugal-vortex. Pumps that combine the two principles described above in operation. Such a unit is a pair of centrifugal and vortex pumps mounted on a common shaft and connected in series. During operation, water first enters the centrifugal wheel, which is responsible for suction, and then to the vortex wheel, which provides pressure. Due to this, it was possible to combine the advantages of both types in one unit — a large suction height, a high pressure and a self-priming device. However, these units cost accordingly.
— Vibratory. The term "membrane" is also used. The action of vibration pumps is based on the use of a flexible membrane, equipped with a device that makes it vibrate. This membrane is one of the walls of the working chamber, and the chamber itself has inlet and outlet valves. When the membrane moves "out" and the volume of the working chamber increases, the inlet valve opens (the outlet is closed), allowing fluid to enter; and when the membrane moves “inward” and pushes the liquid out, on the contrary, the outlet opens. The main advantages of this device are simplicity, compactness, versatility, low cost, ease of regulation and almost complete insensitivity to dry operation. At the same time, the service life of such units is relatively short due to the strong wear of the membrane.
— Auger. The main part of such pumps is precisely the auger — a rotor (or several rotors) in the form of a screw. This design makes the pump very reliable, allows it to achieve high outlet pressure and uniform liquid supply, provides self-priming (see "Suction type"), and also has a low noise level. At the same time, auger units are difficult to manufacture and, accordingly, expensive.
Suction height
The largest difference between the height of the pump and the height of the water level at which the pump can provide normal suction. Without special devices, the maximum value of this parameter is 7-8 m — this is due to the physics of the process. However, when using an ejector (see below), the suction height can be increased several times.
Ejector
The presence of an ejector in the design or delivery set of the pump.
The main purpose of the ejector is to increase the effective suction height. Its action is based on the fact that part of the water pumped by the pump is sent back down to the intake point; this water in some way "pushes" the water in the main suction line. Thanks to this, the suction height can be increased from 7-8 m, available without an ejector, to 15-20 m. The main disadvantage of this device is a rather high noise level.
Maximum power
Rated power of the pump motor. The more powerful the engine, the higher the performance of the unit, usually, the greater the pressure, suction height, etc. Of course, these parameters largely depend on other features (primarily the pump type, see above); but models similar in design can be compared in terms of power.
Note that high power, usually, increases the size, weight and cost of the pump, and also implies high costs of electricity or fuel (see "Power source"). Therefore, it is worth choosing a pump according to this parameter taking into account the specific situation; more detailed recommendations can be found in special sources.
Impeller / auger material
The material from which the main working element of the pump is made is an impeller, an auger or a membrane. This part is in direct contact with the pumped liquid, so its specs are key to the overall performance and capabilities of the pump.
— Plastic. Plastic is low-cost, and it is not subject to corrosion. It is believed that the mechanical strength of this material is generally low, and it does not tolerate contact with solid impurities. However, today there are many varieties of plastic — including special high-strength varieties that are suitable even for working with heavily polluted water or sewage. So plastic impellers/augers can be found in a variety of types of pumps; the overall quality and reliability of such parts, usually, depend on the price category of the unit.
— Cast iron. Solid, durable, reliable and, at the same time, relatively inexpensive material. In terms of corrosion resistance, cast iron is theoretically inferior to more advanced alloys like stainless steel or aluminium; however, subject to the operating rules, this point is not critical, and the service life of cast iron parts is no less than the total service life of the pump. The unequivocal disadvantages of this option include a large mass, which slightly increases the energy/fuel consumption during operation.
— Stainless steel. By the name, one of the key advantages of stainless steel is high resistance to corrosion — and, accordingly, reliability and durabili...ty. Such an alloy is somewhat more expensive than cast iron, but it also weighs less.
— Aluminium. Aluminium alloys combine strength, reliability, corrosion resistance and low weight. However, such materials are quite expensive — more expensive than the same stainless steel, not to mention cast iron.
— Brass. The varieties of brass used in pumps are distinguished by high strength and hardness, as well as insensitivity to moisture. Such materials are quite expensive, but this price is fully justified by the mentioned advantages. Therefore, in certain types of pumps — in particular, surface models and pressure tank units — brass impellers are very popular.
— Bronze. A material similar in many properties to the brass described above. However, bronze is used much less frequently — in particular, due to a slightly higher cost.
— Steel. Varieties of steel that are not related to stainless steel are used extremely rarely — in certain models of pumps for chemical liquids. At the same time, steel is usually used as a base in such parts, and a coating of fluoroplastic or other similar material is applied to it to protect it from corrosion.
— Silumin. Silumins are called aluminium alloys with the addition of silicon. For several reasons, such materials are rare in pumps, and mainly among relatively inexpensive models.
— Rubber. Material traditionally used for diaphragms in vibratory pumps (see “Pump type”).
