Combination of constant pumps comprising n individual pumps that are geometrically tiered such that 2n—1 delivery flow steps are obtained. By enabling and disabling (unpressurised idle circulation) individual pumps the overall pump delivery flow can be adjusted to demand.
Digital pumps are only used infrequently these days. Instead the easier to use but also more expensive variable pump is used with a delivery flow that must be equal to ΣQ n.