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Pressure Sustaining Valves (PSVs) throttle (ie. limit or restrict) flow to maintain a user-defined upstream pressure or hydraulic grade.
When a PSV is throttling flow:
PSVs are useful in situations where unregulated flow would result in inadequate pressures (too low) in the upstream portion of a system.
The valve can be in one of three states.
Reverse flow through a PSV is allowed when the "Status (initial)" is set to Inactive.
When the PSV's "Status (initial)" is set to Active, reverse flow is not allowed and "Status (Calculated)" will be set to Closed.
When the PSV's "Status (Initial)" is set to inactive (ie. fully open):
For: "Setting Type" = Pressure
Pressure Setting (Initial)
Status (Calculated)
55psi
Inactive (1)
65psi
Active (2)
80psi
Closed (3)
(1) If the PSV's "Pressure Setting (Initial)" is below the upstream pressure when "Status (Initial)" is set to inactive. Then the "Status (Calculated)" is set to Inactive (ie. fully open) as there is no throttling necessary. This is because even with the PSV fully open, the upstream pressure is already higher than required and any throttling would just increase the pressure more.
(2) If the PSV's "Pressure Setting (Initial)" is above the upstream pressure when "Status (Initial)" is set to Inactive, and throttling the PSV will allow the "Pressure Setting (Initial)" to be maintained, then "Status (Calculated)" is set to Active (ie. partially open).
(3) If the PSV's upstream pressure can't be raised to the value defined for "Pressure Setting (Initial)", then the "Status (Calculated)" is set to Closed to provide the maximum upstream pressure.
Similarly, for: "Setting Type" = Hydraulic grade
Hydraulic Grade Setting (Initial)
160ft
Inactive (4)
175ft
Active (5)
200ft
Closed (6)
(4) If the PSV's "Hydraulic Grade Setting (Initial)" is below the upstream hydraulic grade when "Status (Initial)" is set to inactive, then the "Status (Calculated)" is set to Inactive (ie. fully open) as there is no throttling necessary. This is because even with the PSV fully open, the upstream hydraulic grade is already higher than required and any throttling would just increase the hydraulic grade more.
(5) If the PSV's "Hydraulic Grade Setting (Initial)" is above the upstream hydraulic grade when "Status (Initial)" is set to Inactive, and throttling the PSV will allow the "Hydraulic Grade Setting (Initial)" to be maintained, then "Status (Calculated)" is set to Active (ie. partially open).
(6) If the PSV's upstream hydraulic grade can't be raised to the value defined for "Hydraulic grade Setting (Initial)", then the "Status (Calculated)" is set to Closed to provide the maximum upstream hydraulic grade.