A motor pump is a surface pump coupled to a petrol or diesel engine for total autonomy. Flow, pressure, delivery head, HMT and granular passage are its main characteristics. Used to pump pond, flood or swimming pool water, it is also used for watering.


Important features

  • Petrol or diesel engine
  • Flow and pressure
  • Total head
  • Delivery height
  • Nature of the water to be pumped
  • Self-priming or manual priming
  • Autonomy in number of hours of use


The main criteria for choosing a motor pump

A motor pump is chosen according to several criteria:
  • the nature of the water pumped either very charged (≥ 20 mm), charged (impurities ≤ 20 mm), clear (impurities ≤ 5 mm);
  • the delivery head either the height in meters (m) between the motor pump and the point where the water is pumped;
  • suction depth measured in meters (m), maximum 8 m;
  • the flow expressed in liters / minute (l / min) or cubic meters / hour (m3/ h);
  • autonomy in hours of use ;
  • the motorization according to the frequency of use, either with a 2-stroke petrol engine for occasional use and low pumping requirements, with a 4-stroke petrol engine for occasional to frequent use, with a diesel engine for intensive use;
  • pressure if the motor pump operates devices requiring a defined inlet pressure (B);
  • the length of the discharge pipe between the motor pump and the point where the water is pumped (measured in meters) to estimate the pressure drops (1 m = 1 B = 10 mCE)
Depending on the use and the information given by the manufacturers, you may be required to calculate total head (HMT) by cumulating the delivery head (m), the desired pressure at the discharge point (convert 1 B for 10 m) and the pressure losses (m).

What is a thermal motor pump

Detailed view of a motor pump

Definition and operation

A motor pump pump water at point A to discharge it at point B, it works with a combustion engine.
The operating principle of a motor pump is relatively simple: a heat engine drives a hydraulic pump with wheel, turbine, or blades, creating a vacuum at the suction and an overpressure at the discharge. The heat engine can be diesel, gasoline, 2 or 4 stroke. Depending on the motor pump, the water is sucked at a given depth (max. 8 m) to be pushed back to a given height and all under pressure.
Portable et autonomous the heat pump is the pumping solution most versatile and the easiest to use. In short, it is a surface pump coupled to a generator. Its installation can be fixed but it is very rare.
There are few wear parts, maintenance is simple, And the lifetime of the assembly is generally high if the motor pump is correctly used and maintained.
Pumps are commonly started with a launcher.
Note: pumping more than 8 meters deep is carried out with a submerged pump.

Granulometry: the nature of the water to be pumped

The grain size, or granular passage, determines the maximum diameter of debris and suspended matter (MES) that can be pumped by the pump. The granular passage of the pumps is not standardized, the intake values ​​oscillate up to 5 mm in the same class from one manufacturer to another (always check the accepted value).

Clear waters

Clear water corresponds to swimming pool water, river water (withdrawal under authorization) or well water. Clear water motor pumps offer a very low granular passage <5 mm. Beyond that, the aspirated MES clogs the pump body.

Loaded or flood water

Sewage, flood water, pond or pond water are likely to be loaded with various suspended matter for this reason, any motor pump used for lifting this type of water offers an accepted particle size of 10 to 20 mm.

Highly charged waters

Highly charged waters present debris greater than 20 mm. This water corresponds to mud, flood water or any loaded water (paper, wipes etc.). Their granular passage is greater than 20 mm. To facilitate the passage of MES, certain motor pumps are equipped witha macerating wheel responsible for crushing debris to facilitate their passage.

Aggressive waters

Aggressive waters are represented by sea ​​water, non-explosive petroleum products, etc… These very specific uses require stronger pump bodies and materials provided for this purpose. Likewise, the temperature of the pumped liquid can be the subject of a selection criterion. Check the permissible temperatures in ° C of the motor pump.

Motor pump: petrol or diesel engine

Petrol motor pump

Gasoline engines are recommended for occasional use, they are quieter than their diesel counterpart and are mainly represented by 4-stroke engines. Maintenance is equivalent to any other engine and is limited to check the oil level, the air filter et the candle. Starting is also easier, even after a prolonged shutdown.
In terms of cost, the petrol engine is less expensive than the diesel engine and remains lighter To manipulate. Motor pumps with smaller displacements are available with 2-stroke engines, they operate with a mixture (petrol + oil in the same tank).

Diesel motor pump

Diesel engines are recommended for intensive use and regular. They generally equip motor pumps with strong powers (especially those used in fire defense) and are much more noisy. Their maintenance is more rigorous as is their start-up - large motor pumps have a electric starter.
A diesel pump is more expensive than petrol, maintenance is more regulatedand more pointed: starter, glow plugs, filters, oil level, injectors. Diesel generators are often mounted on a chassis fitted with wheels to facilitate handling.

Impact of engine displacement on performance

The displacement of an engine is measured in cubic centimeters (cc or cm3), she is relating to the volume of the cylinder combustion chamber (depending on the distance between the top and bottom dead center of the piston and the cylinder bore) and partly determines the power of the engine, itself sized according to the desired pumping characteristics. Prefer a pump with a larger displacement for equal pumping characteristics because at identical performance, its speed is lower which preserves the engine.

Flow, pressure, HMT: the key characteristics of a motor pump

Flow: m3/ h or liters / min

The flow rate is the characteristic that determines the volume of water pumped and discharged by the pump over a period. Expressed in cubic meters per hour (m3/ h) or in liters per minute (l / min), it is chosen according to the volume of water to be pumped and the time available.
Note that 6 m3/ h is equal to 100 l / min and the flow rate varies according to the suction depth and the height of the discharge point.
Indeed, for the same pipe diameter and for the same pump, the greater the difference in height, the less flow you have. Conversely, the closer your suction and discharge points are in terms of height, the higher the flow will be.


The pressure defines the force of the water at the discharge. It relates to the flow rate, to the section of the pipe and is measured in B (bars). Does not affect if the motor pump is only used for water drainage, the pressure is decisive if the motor pump is connected to devices requiring a precise inlet pressure (sprinkler system). Many manufacturers report the total head (HMT) measured in meters (m). Note for correspondence that a bar equals 10 mCE. If this is the case for the pump you are looking for, you will need to calculate the HMT. Also, the pressure goes hand in hand with the flow, it is one of the laws of hydraulics : for the same flow rate, the pressure varies according to the section of the discharge pipe.

Example: a pump with a working pressure (at the pump outlet) of 2,5 B or 25 mWC gives, if the discharge is at the same height as the pump, 2,5 B of outlet pressure. Yes the discharge is 10 m above the pump, only 1,5 B in outlet pressure will be available.

Total manometric head: HMT

Total head summarizes a pumping situation. That is to say, it is calculated en cumulant suction height (HA) between the water point and the pump, the delivery head (HR) between the motor pump and the discharge point, the required outlet pressure in bars (B) and pressure losses summarized by the length of the discharge pipe and fittings (10 m = 1 B or add 10%).

Example of pumping situation

  • HA: 3 m (the bottom of a swimming pool for example with the pump placed on the ground)
  • HR: 2 m (which separates the motor pump from a sewer-type evacuation network)
  • Pressure required: 2 bars (i.e. 20 mCE)
  • Pressure drop: 10% due to lengths of pipes and fittings.


  • (HA + HR + pressure in mCE) + pressure drop = (3 + 2 + 20) + 10% = 27,50 HMT


If the suction height is equal to or greater than 8 m, direct your choice to a submersible pump because the suction is too great for any motor pump.

Performance curve

Given that flow / pressure / HMT correlation is not necessarily obvious to everyone, motor pump manufacturers often indicate the relationship that exists between all these parameters by a performance curve easy to read.
The curve indicates according to a delivery head the corresponding flow.
Do not hesitate to consult it.

Priming, autonomy and weight: the criteria of comfort of use

Self-priming pump and manual priming pump

A self-priming motor pump is a motor scooter , here does not contain air at the intake, it can therefore propel water optimally without heating and without manual intervention.
Motor pumps with manual priming need to be manually primed at each start (a tank is provided for this purpose).
Today, most motor pumps are self-priming for a larger comfort in use and saving time at start-up.

Autonomy of use

Important criterion, especially if you plan to use your motor pump nomadically. Measured in hours, the autonomy corresponds to fuel consumption and tank capacity and translates as the number of operating hours for a full tank of fuel.

Weight of motor pump

The weight of motor pumps ranges from 8 to 100 kg and remains relative to the characteristics of the pump. The heaviest motor pumps are on frame and wheels to facilitate their handling. With equal characteristics and in nomadic use, prefer the lightest motor pump.

Strainer and suction pipe: the accessories required for pumping

The suction strainer

La suction strainer is located at the end of the pipe and constitutes the first filter since immersed in the water to be pumped.
Designed brass with a stainless steel sieve. Its connection must be dimensioned with that of the suction pipe (often 1 inch said 26 x 34 mm).


The fittings are used to connect the pipes to each other and to the pump if necessary.
In fixed installation, they can be made of elbows or even tees. Changes of direction constitute pressure losses.

The suction hose

Le suction hose is available in different diameters (1 inch, 2 inches, etc.).
It depends on the pumping characteristics of the motor pump.

How to use a 5-point motor pump

  1. Regardless of the type of motor pump chosen, it is imperative to pay attention to the engine maintenance recommended by the manufacturer. Change the oil, clean and replace the spark plugs, blow out the air filter guarantees optimal engine operation.
  2. Check before each use the oil level, the condition of the air filter and the fuel level.
  3. If the pump is not self-priming, add water to the tank provided for each start-up test (otherwise there is a risk of overheating and the engine jamming).
  4. Check the tightness of the various fittings during each use, especially if the motor pump is powerful.
  5. The accidents caused by "Dancing pipes" are frequent. If a connector is blown, first shut off the pump before working on it.