On-Demand Priming Systems
On-Demand Priming Systems are used to rapidly establish a prime to a single pump just prior to the need for start-up. On-Demand Vacuum Priming Systems are usually applied with pumps that are used infrequently or when priming is required only when water levels drop below normally flooded suction conditions. Simplex Vacuum Priming Systems or Duplex Vacuum Priming System designs can be employed for this service, and they do not require the use of a vacuum receiver for a simplified compact installation. When furnished with engine drives, these systems are easily portable making them ideal for irrigation, de-watering and other remote priming applications.
On-Demand Vacuum Priming System size is based on the desired or acceptable amount of time to establish the prime. Sizing involves determining the airflow necessary to evacuate the volume of air in the suction pipe within the required time. All aspects of the On-Demand Priming System design from layout of pump suction piping that must be primed, to the priming valve size and type necessary for a properly functioning system are considered. Figure 1 shows a typical connection for an On-Demand Vacuum Priming System. The priming valve isolates the suction side piping from the vacuum side. Typical priming valves incorporate a float actuated closure against an orifice seat as depicted in the system shown in FIG 1 above. These valves need to be sized for the required flow rate of the system. When flow rates are very high or when dealing with liquids having a tendency to foam, a priming chamber such as shown in FIG 2 above is better suited to the application.