Body Pressure Pressure Vessel Burst Rating Measured in psi Failure Threshold of the Vessel
Body Pressure ANSI Body Rating Relationship between Pressure and Temperature
Close-Off Pressure The maximum pressure that a valve can withstand without leakage while in the fully closed position. P1P1
Close-Off Pressure Rule of Thumb 2-way Valve Close-off pressure should at least equal the maximum pressure produced by the circulating pump 3-way Valve Close-off pressure should at least equal the system differential pressure
Close-Off Pressure Close-Off Leakage Bubble Tight is not an ANSI rating. Bubble Tight implies No water leakage.
Pressure Drop P1P1 P2P2 The maximum allowable pressure differential that a fully open valve can withstand without damaging the internals of the valve.
Temperature Ratings Media Temperature (hydronic) Acceptable fluid temperature range Media Temperature (steam) Commonly measured in lbs of steam Ambient Temperature Usually an actuator rating
Characterization Curves Equal Percentage Linear Quick Opening Modified Equal Percentage Valve Position Flow Modulating Control of a Coil CCV, PI-Valves, Globe Valve Modulating Control of Steam Coil or Bypass Applications ePIV, Globe Valves 2 Position control Zone Valves Varies based on design Butterfly Valves, others
Rangeability & Turndown Rangeability: The ratio of maximum flow to minimum controllable flow of a valve body only under laboratory conditions with a constant differential pressure applied across the valve. Turndown Ratio: The ratio of maximum usable flow to minimum controllable flow of the valve assembly under installed conditions. It is always lower than the rangeability factor.
Hydronic Valve Sizing Differential Pressure Across the Valve Should be greater than coil DP Valve Authority > 0.4 Typically between 3psi - 5psi for modulating Typically about 1 psi for on/off Rules of Thumb
Pipe Reduction Factor ½" valve in a ½" pipe with a Cv tested at 10 Same ½" valve in a 1" pipe will test at Cv = 6.3
Only for Valves with High Cv relative to line size
Pipe Reduction Factor Choosing Valves Smaller than Line size The control valve shall be no less than ½ the pipe size… However, it’s best to keep the valve size reduction no greater than 2 pipe sizes. Large pipe reductions can increase the effects of cavitation Rules of Thumb
Piping Considerations Which is Correct? And Why is it Correct? day month yearTemplate 32
CCV Pros Inexpensive Equal Percentage Characteristic High Close Off Large Range of Cv Cons Hot and Chilled Water with Glycol Only Applications Hot & chilled water coils (for air handling units) Unit ventilators Fan coils VAV units Valve Summary
Globe Valves Pros Equal Percentage or Linear Characteristic SS Trim works for Steam Cons Expensive Large 2 Versions of 3-way Close off depends on Actuator Applications Hot & chilled water coils (for air handling units) Chillers Valve Summary
Pu Pd Holes in Plate Balance the Pressure What is a Pressure Compensated Globe Valve? Globe Valves
3-Way Butterfly Valves 2 Valves linked on a Tee Mixing or Diverting 1 or 2 Actuators
Butterfly Valves 3-Way Butterfly Valves 2 Valves linked on a Tee Mixing or Diverting 1 or 2 Actuators
Butterfly Valves 12 ft/sec in Standard BFV 32 ft/sec in High Performance BFV Sizing a BFV: Velocity
Butterfly Valves Pros Up to 30” Inexpensive High Close-Off SS and HP Available Cons Modified Eq % High Cv Relative to Size Velocity Limitations Applications Chiller and Cooling Tower Isolation Change Over Systems Large Air Handlers Bypass Controls Valve Summary
Pros For extreme applications High Temp Water High Pressure Steam High rangeability Cons Expensive Limited sizes and Cv Large (heavy) Applications Hot & chilled water coils (for air handling units) Chillers Valve Summary
Zone Valves Inexpensive 2 Position Spring Return “Paddle” Design Zone Valves
Zone Valves Pros Cheap Fail Safe Cons Cheap 2 Position Only Low Close-Off Applications Baseboards Low Flow needing 2 position, fail safe Valve Summary
Pressure Independent Valves Pressure Independent Control Valves 2-way valve that supplies a specific flow for each value of the control signal – – Regardless of pressure variations in the system PI Valve Pressure Flow
Pressure Independent Mechanical RegulatorElectronic Flow Meter Technologies
Pressure Independent Valves Pros Accurate Flow Regardless of Pressure Conditions Increased Water-side DT Reduced Pump Energy Usage Valve Authority = 1.0 Eliminates need of Automatic Balancing Valves Cons Higher Initial Cost Applications Hot & chilled water coils (for air handling units) Unit ventilators Fan coils VAV units Valve Summary
Control Valves: Specifications, Sizing & Technologies Questions?