Venturi pumps operate completely without moving parts except for the material moving through them. They work on the principle of conservation of energy where high potential kinetic energy in one fluid entrains another fluid and then propels the mixture out of the pumping area. This quality makes them useful for pumping liquid with a high percentage of solids such as slurries or sewage without clogging or contamination of mechanical apparatus. This DIY venturi pump system is handy for removing mud and other solids from basements and sumps where other pumping methods would stall from clogging.
Standard venturi pumps
Many back up sump-pumps use the venturi principle where a pressurised flow stream of utility water is directed into the throat of a converging venturi, where it induces a partial vacuum that then draws water to fill the void. The kinetic energy of the higher-speed stream is imparted to the mixture of the entrained liquid and propelling liquid, and is proportional to the mass of the mixture. These units use a lot of clean water to move the entrained liquid, however, with many requiring at least 4.55 litres (1 gallon) per minute to entrain 9.1 litres (2 gallons) of waste liquid, for a sum total of 13.65 (3 gallons) ejected from the end of the pump.
A slight twist
The trick with this system is that it uses an extremely high-pressure stream from a pressure washer to drive the venturi pump. This system has a much lower flow, but a much higher kinetic energy to inject into the venturi, which serves several purposes. First, the ratio of volume of powering water to water ejected from the pump is much lower, bringing greater effectiveness and efficiency. Second, the high energy stream is able to disintegrate whatever solids there are in the venturi and the downstream pipeline. Finally, the kinetic energy of this system is so high that it is more easily able to self-prime and remain clog-free.
Assemble a PVC pipe fixture starting with 5 cm (2 inch) diameter Schedule 40 PVC pipe and fittings. About two inches from a 90-degree Tee fitting, install a 5 cm (2 inch to 3.7 cm (1-1/2 inch) reducer. Plug in ac1/2 NPT internal thread adaptor to the side of the Tee opposite the reducer. Buy a compression fitting that fits the brass wand tube of the pressure washer tip. Unscrew the tip fitting, slide on the compression fitting and reinstall the tip. Now insert the pressure washer tube including tip and compression fitting into the PVC pipe adaptor, and thread tight. Teflon tape on the threads will assure a tight seal.
Test the venturi pump
Connect the DIY venturi pump to 3.7 cm (1 1/2 inch) vinyl hoses with hose adaptors on either end. Put the suction end into a 22.5 litre (5 gallon) pail of clean water and squeeze the washer handle. With the compression fitting slightly loose around the tube, slide the nozzle back and forth into the reducer fitting until the maximum outlet flow is achieved. This will be the optimal setting, and the place where the compression fitting should be tightened around the pressure washer wand.