A hydraulic variable displacement pump has a method of increasing or reducing displacement either manually, hydraulically or electronically. The method of displacement change depends upon the pump’s structure, differing between piston and vane pumps. Read More

The displacement of a pump is defined by the theoretical volume the gears, vanes or pistons will displace in one revolution. If a hydraulic fixed pump is 30 cc, it will theoretically push 30 ml of fluid in a single rotation, or about 1.8 in.3. With a fixed displacement hydraulic pump, these 30 cm3 do not change, regardless of how the hydraulic fixed pump is controlled or what occurs downstream. In reality, actual flow varies based on efficiency, speed and pressure, but that’s a different story. If you need less flow than the hydraulic fixed pump is rated for, the excess flow must be diverted or relieved to tank. Read More