How to choose a thermal fire 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).

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 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 regulatedr and more pointed: starter, glow plugs, filters, oil level, injectors. Diesel generators are often mounted on a chassis fitted with wheels to facilitate handling.

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.

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.

Pressure

Pressure defines the force of water at discharge. It is related to the flow rate and the pipe diameter and is measured in bars ( B ). While insignificant if the pump is only used for drainage, pressure is crucial if the pump is connected to devices requiring a precise inlet pressure (such as an irrigation system). Many manufacturers specify the total dynamic head (TDH) measured in meters (m) . Note that one bar is equal to 10 meters of water column (mWC). If this is the case for the pump you are considering, you will need to calculate the TDH. Furthermore, pressure is directly related to flow rate; this is one of the laws of hydraulics : for the same flow rate, the pressure varies according to the diameter 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

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

• 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

Important

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

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.

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.

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.

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.

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.

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