Priming System Sizing

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Priming System Sizing

Proper sizing of a vacuum priming system is based on the required volume of air to be removed from the suction piping within the acceptable period of time. Sizing also depends on whether operation of the system is On Demand, where priming is done before each time a pump needs to start or Automatic systems that maintain a constant prime for immediate start-up.
Proper sizing of a vacuum priming system is based on the required volume (V) of air to be removed from the suction side piping and the required lift (h) of the water from the reservoir to the centrifugal pump. The required vacuum (PREQ) to establish a prime is determined from the following simplified formula.

P_REQ = P_ATM - ρ _x g _x h

at standard S.L. conditions we have

P_REQ (“Hg absolute)= 29.92 – 0.88 x Feet of Lift

Sizing for On-Demand Priming Systems

With On-Demand Priming Systems, priming is done before each time a pump needs to start. On-Demand Priming Systems are sized based on being able to establish a prime within a given amount of time (T). To determine the required average system capacity (QAVG) in ACFM we use the following formula.

Q_AVG = V x P_ATM x ln(P_ATM/P_REQ) / (T x (P_ATM-P_REQ))

NOTE: Pressure values are to be in absolute units, volume (V) in Ft³,

time (T) in minutes, and ln is the natural log.

Sizing for Automatic Priming Systems

Automatic systems maintain a prime to one or several (Central System) pumps for immediate start-up whenever needed. Withautomatic priming systems, once the system is primed, minimal vacuum pump capacity is required to maintain the prime. However, the priming system needs to be sized with sufficient capacity to be able to establish the initial prime within an acceptable period of time. Our systems are generally sized to establish the initial prime within 10 to 20 minutes. Once the initial prime has been established, the system automatically maintains a prime state for immediate startup of all connected centrifugal pumps as they are needed.

Proper system sizing for most applications can be determined by using the table below along with the following guidelines:

1.Calculate the total volume of the system including the suction pipe, casing volume of the pumps that needs to be primed, and discharge piping to the stop valve.

2.From the table, select the corresponding model, simplex or duplex, which correlates to your calculated system volume.

3.For priming (5) or more centrifugal pumps, select the next larger primer size.

4.For lifts greater than 15ft. priming times will be longer and you may want to select the next larger primer size. For lifts greater than 25ft. or any special applications, consult with a LYNN engineer for assistance with the proper selection.

Receiver tank size shown is the standard size for a particular model. Depending upon the specifics of the application other receiver sizes may be suitable.