Determining the proper system type and sizing for the application is the first step in selecting a vacuum priming system. Selecting the proper type of system depends upon the application requirements of the pump or pumps that require priming. There are two system types to consider, On-Demand priming or Automatic priming. Each system type is also available in either a simplex or duplex version.
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. These 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 designs are usually 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.
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 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 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.
Automatic Priming Systems
Automatic priming systems are used when one or multiple pumps are required to start without delay. Once intial prime is established the system continues to automatically maintain the prime, allowing immediate start-up of pumps in stand-by. The standard design for these systems is to automatically maintain a prime through pressure control of the system’s operation. Each connected pump and any isolated high points in the suction piping requires a priming valve. The priming valve has a float actuated seat to isolate the priming system from suction piping. Through pressure control operation, the priming system maintains a vacuum between a high and low set point to the connected system’s priming valves. The low set point is always greater than the vacuum required to fully prime all pumps connected to the system.
Level controlled systems are also an option. The application of these systems is suitable when all pumps needing a prime are located at the same level and take their suctions from the same level. The system automatically cycles on and off to maintain a water level range within the receiver, and eliminates the requirement of priming valves. Variations in the operating configurations of these two system types are available to meet the needs of special installations.
FIG 3 above shows a typical layout for a pressure controlled automatic priming system. With this type of system there are few restrictions to where pumps are located or whether suctions are taken at different levels. With proper consideration in the layout of the interconnected vacuum piping between the priming system and the pumps, the priming system can be located wherever is most convenient.
Automatic priming systems are available in either simplex or duplex versions. Compared with self priming pumps, an automatic priming system allows selection of the most efficient pump for the application. They offer the broadest range of application, handling the highest suction lift with small or large capacity systems.
Simplex or Duplex Considerations
All LYNN priming systems are available as either a simplex or duplex model. Deciding which is the right choice depends on your application requirements.
LYNN Simplex Priming Systems are an ideal choice with non-critical applications. Simplicity in design and operation, this is a reliable, economical solution and can be used with either On-Demand or Automatic priming applications.
For critical applications or when priming several pumps off one system (Automatic Priming System), a LYNN Duplex Priming System is the recommended choice. Both vacuum pumps are used to establish the initial prime. The system then alternates between vacuum pumps to maintain the prime. In the event one pump cannot keep up with the load, the second vacuum pump automatically comes on. Or if one of the vacuum pumps fail, the priming system remains functional. Furthermore, with the advantage of being able to run both vacuum pumps during initial prime, a smaller system can often be used to replace a suitably sized simplex system.
Optional features which enhance reliability or operational control can be added to any system.
For the ultimate in protection and reliability all systems are available with LYNN Automatic Tank Drain assemblies to continually drain off accumulated condensate without having to shutdown the system.
For systems furnished with oil lubricated vacuum pumps, LYNN Automatic Purge Control eliminates the potential damage to vacuum pumps from flooding and condensation build up in the vacuum pump’s lubricating oil. LYNN Automatic Purge Control operates automatically with each On/Off cycle of the vacuum pump. This feature also includes an upgrade to a two (2) year system warranty.
Numerous other options including special control features, alarms, corrosion protection, coatings, materials of construction can compliment any system.
For further assistance with design and selection of a vacuum priming system for your application contact an expert at LYNN.