Diaphragm pumps have very significant properties, which make them particularly suitable for use in agriculture on spraying bars and air-blast sprayers. The 3 main advantages of a diaphragm pump compared to a centrifugal pump are:
- Excellent head and self-priming capacity.
- Good dry running capacity
- Resistance to abrasion and corrosion
The diaphragm pump is a type of pump which uses alternating variations in the volume of a chamber (expansion and contraction) to generate imbalances in pressure between the chamber and adjacent spaces.
Trying to compensate for the difference in pressure between two environments, the fluid naturally moves from the space with greater pressure to the space with lower pressure, resulting in a downward movement, a rise, and in short in the pumping of the fluid itself.
The expansion and contraction of the chamber volume that generate these pressure changes, are obtained by means of the alternating flexing of the diaphragm.
The diaphragm is nothing more than a rubber disc screwed onto the piston which separates the pumping chamber from the transmission parts and prevents the pumped fluid from coming into contact with the mechanical parts and the lubrication oil.
Thanks to the airtightness generated by the diaphragm and the separation between the pumped liquid and the oil bath chamber, using a diaphragm pump has three main advantages:
- EXCELLENT HEAD AND SELF-PRIMING CAPACITY
The diaphragm pump has the ability to create a good vacuum on the suction line. In practice, the diaphragm generates an excellent airtight seal and a consistent vacuum on the suction line, which means that a diaphragm pump can lift fluids from levels lower than those in which it is located (head capacity). Lifting between 3 and 3.8 metres (9.8 and 10.5 feet) is normal for a diaphragm pump, with the obvious advantage of being able to draw liquids from the channels or basins below it and an enormous benefit when loading tanks.
In addition, a diaphragm pump can be operated without the need to fill the suction pipe (unlike the centrifugal pump), thanks to the fact that it is able to suck up the air contained in the suction pipe during the start-up phase, and eliminate such air through the delivery line (self-priming capacity).
After having eliminated all the air, the pump operates normally.
- GOOD DRY RUNNING CAPACITY
Thanks to the airtight separation between the pumping chamber and oil-bath lubricated transmission components, diaphragm pumps can withstand reasonable periods of dry running (e.g. when operating in self-priming mode or in the event of a break in the suction line) without negative consequences, such as overheating and seizing up of connecting rods and pistons, which occur on centrifugal pumps that cannot work dry.
- RESISTANCE TO ABRASION AND CORROSION
Because there are no mechanical parts in direct contact with the liquid (as we have said, the diaphragm creates a airtight seal between the pumping chamber and the transmission components), the diaphragm pump can pump liquids that are not perfectly filtered with residues of solid particles such as crystals, sand or crushed stone (mechanical resistance) and can be used with most water-based plant protection substances, including when mixed with acids, solvents, abrasive particles, sediments or slurry (corrosion resistance).
As you can see from the picture, the diaphragm separates in an airtight way the blue compartments, in which the pumped liquid flows, from the oil bath chamber in which the mechanical components are located (in yellow).