A differential pressure metering apparatus includes a manifold for fluidically coupling impulse lines. The manifold also includes a rigid body having a base, and an arm extending from the base, with a high and low pressure channel extending through the body from a high pressure inlet to opposing first and second high pressure outlet ports, and from a low pressure inlet to opposing first and second low pressure outlet ports respectively. The manifold is configured to be mounted to a flow restrictor pipe section in a wet-line configuration, in which the first high and low pressure outlet ports define impulse line extension directions having a downward component, and the second high and low pressure outlet ports define impulse line extension directions having an upward component.