Finish Thompson SP Series Self-Priming Pumps
They don't suck.
(and other interesting facts about our SP Series)
SP Series pumps really don’t suck – Self-priming pumps create a vacuum (negative pressure) in the suction pipe and atmospheric pressure (positive pressure) pushes the liquid up the pipe to the pumps suction.
Atmospheric pressure - Affects lift capabilities. As altitude increase, the pressure of the atmosphere is reduced. This reduces the “pushing force” on the liquid in the suction pipe. Lift is reduced by 1.13 feet (.34 m) for every 1,000 feet (304 meters) of altitude. Altitude also affects NPSHa, less “pushing force” on the fluid entering the pump.
Specific gravity – It takes more force (provided by atmospheric pressure) to push heavier liquids up the suction pipe than it does water, just like it takes more effort to lift heavier weights when exercising. To adjust the maximum lift, divide 25 feet (7.6 meters) by the specific gravity of the fluid.
Gooseneck – Not a bird part but the internal design of the SP Series that allows us to eliminate troublesome internal check valves or foot valves. The gooseneck breaks the siphon affect when the pump is stopped and liquid wants to return to the source retaining sufficient liquid for re-priming.
Size does matter – Larger diameter impellers not only produce more flow and head but also reduce priming times. An increase in the diameter of the suction pipe (1”/25mm to 1 ½”/38mm for example) will allow increased flow but will increase priming times.
Time is temperature – Say what? The priming liquid in the housing rises approximately 3º F (1.6º C) per minute while the pump is priming. The longer it takes to prime the higher the temperature of the priming fluid. It is important to ensure that the pump does prime and starts pumping.
Head data - The head shown on our SP curves is Total Dynamic Head (TDH), which is equal to the suction lift plus discharge head of the system. For example, if your application requires 15 feet (4.6 m) of equivalent suction lift and 75 feet (22.9 m) of discharge head, you would require a pump that is capable of producing 90 feet (27.5 m) TDH.
Good vacuum pump, poor air compressor – SP Series pumps can achieve high levels of vacuum during the priming process but the as the air in the suction pipe is being displaced by liquid, the air has to go somewhere. Centrifugal pumps cannot compress this displaced air and open a check valve in the discharge line. If a check valve is installed in the discharge piping make sure it is placed at a distance at least equal to the maximum suction lift from the pump (gives the displaced air a place to go). Once the pump primes, the liquid will open the check valve. If this cannot be done, an air vent must be installed in the discharge line.