Alternating volumetric pumps with three semi-hydraulic diaphragms for use in agriculture in low pressure systems for spraying open field crops with fertilisers, pesticides or weed killers. Parts in contact with pumped liquids in plastic-coated aluminium and stainless steel. Diaphragms in NBR. Seals in NBR or Viton. Die-cast casing with oil-immersed mechanism and clear plastic tank for visual level checking. Pistons with ring for a more efficient “oil cushion” system to protect the diaphragm. New-design diaphragm cut-out system to prevent contact tearing even in heavy-duty operating conditions. Spherical sector profile valves for lower flow resistance and improved volumetric efficiency. Rugged feet secured to pump casing. GEOMET coated or stainless steel metal fasteners. Stopper for drainage of liquid from the circuit before storage over winter. Complete with relief valve with manual reset and drive shaft guard.