Liquid feeding pump

A liquid feeding pump which comprises:

• first and second cylinders which are coaxially arranged and separated by a partition, said first cylinder including a head end wall opposite said partition and said second cylinder including a bottom end wall opposite said partition,
• a first piston movably positioned in said first cylinder to define a liquid chamber between said first piston and said head end wall and a first air chamber between said first piston and said partition,
• a second piston movably positioned in said second cylinder to define a second air chamber between said second piston and said partition and a third air chamber between said second piston and said bottom end wall,
• a rod extending through said partition and connecting said first and second pistons,
• first inlet and outlet means communicating with said first chamber for liquid,
• second inlet and outlet means communicating with said first air chamber,
• third inlet and outlet means communicating with said second air chamber,
• fourth inlet and outlet means communicating with said third air chamber, and
• means for passing liquid flowing to or from said first inlet and outlet means around an outer side of said second cylinder to cool said liquid,
• wherein when said liquid chamber contains liquid and said second air chamber is vented, supplying high pressure air to said first and third air chambers will cause said first and second pistons to move such that the first piston will discharge liquid from said liquid chamber through said first outlet means, while venting of said first and third air chambers and supplying high pressure air to said second air chamber will cause said first and second pistons to move such that the first piston will allow liquid to enter said liquid chamber through said first inlet means.