What type of valve should be used with a positive displacement pump that has a negative suction head?

Using a foot valve with a positive displacement pump that has a negative suction head is important because it helps maintain the prime of the pump and prevents backflow. A foot valve, which is a type of check valve installed at the suction side of the pump, is submerged in the liquid and ensures that the pump remains filled with liquid, even when it is located above the fluid level. This is crucial for situations where a negative suction head is present, as it helps avoid issues like cavitation that could lead to pump damage or inefficiency.

In applications involving positive displacement pumps, the foot valve also allows for easy priming, ensuring that the pump can effectively move the fluid without losing suction. This valve's design minimizes the risk of air entering the suction line, which could disrupt the pump's function and cause operational failures.

Other types of valves, like suction valves or ball valves, may not serve the same purpose in maintaining the fluid column in a negative suction scenario. A check valve typically limits backflow but does not inherently maintain the suction necessary for prime in a positive displacement pump, especially when facing a negative suction condition. Thus, the foot valve stands out as the ideal choice for this specific pumping situation.