A fluid pumping device comprising a pump housing (1 101 201 301 701 901) containing a piston chamber (11 101 201 310a, 301b 701 901 ) and a piston (2 102 202 302, 302 702 902, 902 " ) moving back and forth inside the piston chamber, an inlet port (10i 110i 210i 310i 710i 921) and an outlet port (10o 110ο 210o 310o 710o 920) allowing a fluid to be sucked into the piston chamber during an instroke of the piston and expelled from the piston chamber during an outstroke. The device further comprises a valve - switching element (9 109 201 309 701 909 ) movably mounted against a valve base member (7 107 207 307 707 907), which comprises a piston chamber aperture (12p 112p 212p 312p, 312p 1 712p 912p) connected to the piston chamber and an inlet aperture (12i 112i 212i312i712i912i) and an outlet aperture (12o 112o 212o 312o 712o 912o) connected respectively to the inlet and outlet ports of the fluid pumping device. The element comprises a groove (14 114 214 314, 314 714 914) or other recess (514) moving against the valve base member such that, a first communication allows leakage between the inlet aperture and the piston chamber aperture so that fluid is sucked from the inlet port, through the groove or recess, into the piston chamber during part of the piston instroke, while a second communication allows leakage between the piston chamber aperture and the outlet aperture expelling fluid out of the piston chamber, through the groove or recess and the outlet port during part of the piston outstroke.
