| Model B-14 (Open Discharge 8 - 72") - Sizing |
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Once the Bailey valve configuration (Inline, Y-Pattern, submerged,
angle or non-modulating) has been selected, the next step in choosing the best
solution for the application is sizing the valve for the operating conditions.
This is first done by collecting key data, which will be used to determine the
severity of cavitation as indicated by the cavitation index sigma (),
velocity flow and flow capacities (Cv).Once the Bailey valve configuration
(Inline, Y-Pattern, submerged, angle or non-modulating) has been selected,
the next step in choosing the best solution for the application is sizing the
valve for the operating conditions. This is first done by collecting key data,
which will be used to determine the severity of cavitation as indicated by the
cavitation index sigma (), velocity flow and flow capacities (Cv).
Step 1 - DataMaximum Flow Rate => QmaxInlet Pressure at Qmax => Pi @ Qmax Outlet Pressure at Qmax => Po @ Qmax Minimum Flow Rate => Qmin Inlet Pressure at Qmin => Pi @ Qmin Outlet Pressure at Qmin => Po @ Qmin Step 2 - SigmaThe sigma value or cavitation index is calculated and used to configure the performance class of sleeve valve or to determine if alternate options such as ball valves or butterfly valves are acceptable for the application conditions. The following equation is used to calculate the sigma value:
= Po – Pv / Pi – Po
Where: Pi = Inlet Pressure (psig) Po = Outlet Pressure (psig) Pv = Vapor
pressure (-14.6 psig for 60oF water at sea level)
Step 3 - Velocity FlowThe maximum flow rate (Qmax) is compared to the figure in the following table to determine the corresponding valve size based on an allowable continuous velocity of 35 ft/sec through the valve port. Higher velocities can be attained for intermittent operating conditions and it is recommended that you contact the factory for sizing. Your flow rate should be rounded up to the nearest table value and record the corresponding valve size. Various units are provided for simplicity.
Step 4 – Flow Capacities (Cv)The maximum flow rate (Qmax) and associated inlet pressure (Pi) and outlet pressure (Po) are used to calculate the required Flow Capacity or Cv of the application. The Cv equation is as follows: Cv = Q / (Pi-Po) Once the application Cv is calculated from the above equation a safety factor of 20% is added to the value for valve Cv deviation and potential nozzle fouling from entrapped debris within the flow media. The Cv plus 20% value (C20) is compared to the following table to determine the appropriate valve size for the application. The chosen valve size must have a higher capacity than the C20 calculated form the operating conditions. The valve size chosen from the Cv table is then compared to the valve size chosen from the previous table (Velocity Flow) and the larger of the two valves is the correct size for the application conditions.
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