Technologies are described for devices and methods for adjusting a position of impellers within a bowl assembly. The devices may comprise an adjuster at the second end of a spacer coupling. The adjuster may include an adjuster sleeve. The adjuster sleeve may be a cylindrical sleeve. The adjuster sleeve may be threaded on an internal side. The adjuster sleeve may be spaced from the driven hub so that the adjuster sleeve can rotate around a driven shaft. The adjuster sleeve may threadedly mate and engage with an externally threaded first end of the driven shaft when the adjuster sleeve is rotated. The rotation of the adjuster sleeve may adjust a position of the driven shaft with respect to the driven hub and may thereby adjust a position of an impeller attached to a second end of the driven shaft with respect to a stationary bowl.