Small Valves, Large Valves, Fittings, Inlet/Outlet
Overview
This document covers troubleshooting valves, fittings, and fan duty. You will learn how to identify and resolve issues related to pressure, flow rate, and component sizing.
Analyze Flow Rate and Pressure Drop
To troubleshoot flow rate and pressure drop issues, begin by inspecting the system's pressure drop. Pressure drop refers to the pressure reduction across a component caused by flow resistance. The peak flow rate is simply the maximum flow at a given point, derived from the flow in the connected pipes or ducts.
Formulas for calculating pressure drop:
System Type | Formula | Variables |
|---|---|---|
Water Systems | ΞP = k Γ (vΒ²) / (2 Γ g) | ΞP = pressure drop, k = resistance coefficient, v = velocity, g = gravity |
Duct Systems | ΞP = ΞΆ Γ (Ο Γ vΒ²) / 2 | ΞP = pressure drop, ΞΆ = zeta coefficient, Ο = air density, v = velocity |
Factors influencing pressure drop include Kv/Zeta values (industry standard resistance values), graphs (used by some valves to determine pressure drop based on flow rate), pipe/duct size (smaller sizes increase pressure drop), and velocity (higher velocity increases pressure drop). Compare measured pressure drop values with catalog data. Verify the flow rate, velocity, and pipe/duct size. If troubleshooting peak flow rate issues, also refer to the connecting pipe or duct flow rate results.
Assess Pressure Influence
System pressure is affected by upstream components such as flow sources, pipes, fittings, valves, level heights, height changes, and equipment.
To troubleshoot pressure variations: Inspect upstream components for discrepancies. Check flow sources, height changes, and equipment connections. You can also use heat maps to visualize unusual pressure variations.
Determine Component Size
Select component sizes that match connected pipe/duct sizes.
Some components have specialized sizing requirements. If a component's size differs from adjacent pipes/ducts, compare the adjacent pipe/duct flow rate with the component's catalog specifications. Review the overall system sizing configurations.
Understand Kv Values
The Kv value, or flow coefficient, represents the pressure drop for a calculated flow rate.
Calculate Kv values with the formula: Kv = Q Γ β(1 / ΞP), where Q = flow rate and ΞP = pressure drop. Component type, pressure, and velocity all influence the Kv value.
To troubleshoot Kv discrepancies: Check if you can override the Kv value. Consult catalog data for standard values and component-specific graphs. Make sure the velocity and pressure drop are consistent with the Kv requirements.
Examine Fan Duty
Fan duty considers the total flow rate and pressure required by a ventilation fan exhaust system.
To calculate fan duty requirements: Determine the total system flow rate, which should equal the combined flow rates of all connected diffusers or grills. The fan must overcome pressure drops across ducts, fittings, and equipment along the index node path.
To troubleshoot fan duty performance: Verify the fan's flow rate meets the total system demand. Check pressure drop values along the index node path. Use heat maps and design report spreadsheets to pinpoint high-pressure drop areas and adjust them accordingly.