Express Jetting, Plumbing and Maintenance Services are accredited in backflow prevention and servicing. today we are servicing an RPZ for a mechanical workshop. Backflow prevention devices stop water flowing back into main water supply pipes. In this instance the original RPZ failed as it couldn't retain spring tension. after weighing up the cost of a service kit or a brand new RPZ ourselves and the customer decided it was best to supply and install a new RPZ..