Which is the best pump to use if you have to locate it above the surface of the fluid?

The best pump to use when it needs to be located above the surface of the fluid is a bent axis pump. This type of pump operates efficiently with fluid movement and can maintain a prime even when positioned above the fluid level. The design of the bent axis pump allows it to effectively create suction and draw fluid up into the pump casing, making it suitable for applications where gravity assistance is not available.

In contrast, while in-line axial piston pumps, radial piston pumps, and gear pumps can operate in various orientations, they generally rely more on gravity to maintain a prime or may struggle when placed above the reservoir. These types of pumps can be sensitive to changes in fluid levels and may require additional priming mechanisms or configurations to operate efficiently when installed above the fluid surface. Therefore, for installations where the pump is mounted above the fluid, the bent axis pump stands out as the most appropriate choice due to its design features and operational capabilities.