THE KART WATER PUMP

Gianluca Covini

18 February 2024 • 16 min. read

It has the task of ensuring the correct flow of cooled liquid from the radiator to the engine, which is why it can be said that it is the heart of the cooling system of your 2-stroke engine. Why are centrifugal machines mainly used in karting? How can their performance be evaluated? What are the materials most commonly used to make this? We've answered these (and many more) questions so you can master this topic like a pro

WHAT IS IT?

HOW DOES IT WORK?

IN PRACTICE

The cooling of a two-stroke engine, like that of most Racing karts, is one of the main aspects to be managed, in order to ensure maximum performance and reliability of the engine (to learn more, read "Technique | The cooling of the cylinder"). With engines that have a liquid cooling system, there are two components that play a fundamental role: the radiator (which we have put under our magnifying glass in the "Technique | The radiator") and the water pump, which has the function of correctly circulating the water inside the pipes (which, in turn, can be made of different materials, affecting the performance of the entire system differently, to learn more read "Must Have | Pipes for the kart cooling system: pros and cons of the four main types (and a special accessory to match)"). The water pump mainly used on Racing karts is of the centrifugal type. Compared to other types of pumps (such as, for example, the gear pump, the diaphragm pump or the piston pump), the main feature of the centrifugal pump is its ability to provide a high flow rate (amount of water flow in a given time interval, measured in l/min), with a relatively low pressure.

This is exactly what is needed inside a kart cooling circuit, where it is important to have a fast flow of water to remove heat, ideally between 0.5 and 1 m/s, and therefore an equally high flow rate, at least 10-15 l/min, without resorting to large pumps. All this, with a water pressure inside the system that is maintained between 0.5 and 0.9 bar, just enough to avoid the phenomenon of cavitation (a topic that we will explore in a dedicated section). Centrifugal pumps are used not only in karting, but in all those applications where a fast circulation of a light and low viscous fluid with low pressures is required. This type of pump is also called dynamic head pump, because pressure and flow rate are inversely correlated. In other words, as the flow rate increases, the pressure they are able to generate decreases and vice versa.

Liquid-cooled kart engines mainly use centrifugal-type water pumps. The main feature of this type of pump is the ability to provide a high flow rate with a relatively low pressure

WHAT IS IT?

HOW DOES IT WORK?

IN PRACTICE

The water pump’s components

Exploded view of a water pump. It can be seen that the case is made of [1A and 1B] two half-shells, between which is interposed [2] a sealing gasket, made of polymeric material. The two half-shells are fastened by means of [3] screws, usually made of stainless steel. Inside the case is [4] the impeller, moved by [5] the spindle that rotates on the [5A and 5B] bearings. The pulley is also attached to the spindle at the other end [6]. Then there is [7] the pump support to the chassis, which is also fastened with [8] stainless screws. In some models it is adjustable to allow you to find the best angle, i.e. the one that minimizes the bends of the intake and exhaust hoses, thus avoiding the formation of air bubbles in the circuit.

Water pumps consist of: a casing (or pump casing), an impeller, a spindle and a pulley. The shaft is supported by the pump body and rotates on its axis thanks to one or more bearings. The impeller is attached at one end of the spindle, while the pulley is at the other end. Inside the pump body there is a channel, with an increasing section, which directs the water towards the outlet nozzle. In karting, the pumps are driven by the rotation of the axle or the engine, via one or more transmission belts. As far as the FIA Karting technical regulations are concerned, some of the main regulations at international level, only the use of mechanical water pumps driven directly by the engine or axle of the kart is allowed, while electric pumps are prohibited.