Mother nature plays an important role by exerting only 14.7 psi on any body of water at sea level. This limits the suction head of centrifugal pumps to 33.9 feet. However, this would only be obtained if we could achieve a perfect vacuum in the pump. In reality, the suction head of centrifugal pumps is limited to about 26 feet. Pump performance (capacity or pressure) is highest when the pump is operated close to the water's surface. Increasing the suction head will DECREASE the discharge head and consequently the discharge capacity of the pump. Most importantly, suction head should be kept to the smallest value possible to reduce the likelihood of cavitation. Cavitation can also occur if the suction hose is restricted. Never use a suction hose with a smaller diameter than the suction port. Cavitation can quickly damage a pump.