When selecting the size (nominal diameter) of a burner valve train, the primary criteria are the burner's maximum gas consumption and the gas supply pressure of the pipeline network. An undersized valve train restricts gas flow, impairing combustion output, while an oversized one reduces regulation precision or causes sluggish response times during opening and closing. Specific selection involves the following three steps:
1. Determine three key parameters: Before selection, the following data must be confirmed:
Rated/Maximum thermal load (Q): The burner's maximum output power, expressed in kW or kcal/h.
Lower heating value of the gas (H): For natural gas, this is typically 8,500–9,000 kcal/Nm³ or 35.6–37.7 MJ/Nm³.
Gas pressure upstream (P₁) and rated pressure downstream (P₂) of the valve: Determine whether the supply pressure is low (e.g., 2 kPa–5 kPa) or medium-to-high (e.g., 10 kPa–100 kPa).
2. Calculate maximum gas flow rate
Based on the thermal load and heating value, calculate the maximum standard flow rate ($V_{\max}$, in Nm³/h) required for the burner at full load: $V_{\max} = \frac{Q}{H}$
3. Consult selection charts based on flow rate and pressure differential ($K_v$ value method)
The core of valve train selection is its flow capacity ($K_v$ value). The $K_v$ value represents the flow rate of water passing through the valve when fully open with a 1-bar pressure differential across it. Since gas flow calculations are complex, practical guidelines are typically used:
Determine allowable pressure loss: The permissible pressure drop across the valve train is generally 10%–20% of the upstream pressure. The smaller the pressure drop, the larger the required valve train size.
Consult manufacturer specifications: Major burner or valve train brands (such as Dungs, Honeywell, etc.) provide charts correlating flow rate with pressure loss. After calculating \(V_{\max}\), locate the flow rate on the horizontal axis and the corresponding pressure on the vertical axis of the chart based on the available upstream pressure; the curve at the intersection point indicates the recommended valve size.
Quick Reference for Common Valve Sizes (Natural Gas, Supply Pressure approx. 2–3 kPa)
< 100 kW (Small units): Typically Rp 1/2" to Rp 3/4" (DN15–DN20)
100 kW – 350 kW: Typically Rp 1" to Rp 1 1/2" (DN25–DN40)
350 kW – 800 kW: Typically Rp 2" or DN50
800 kW – 2000 kW: Typically DN65 to DN80
> 2000 kW: Typically requires a flanged valve train of DN100 or larger, matched to the specific pressure drop.
Selection Considerations
1. Valve Train Configuration: High-capacity burners (typically > 1200 kW) are required by standards to be equipped with a Valve Proving System (VPS) to ensure no gas leakage when valves are closed; verify whether the valve train includes this feature or has a designated interface for it.
2. Gas Type: If using Liquefied Petroleum Gas (LPG) or town gas, the required \(K_{v}\) value and valve size will differ from those for natural gas due to variations in calorific value and density.
3. Follow Burner Manufacturer's Instructions: It is recommended to consult the burner manufacturer's technical manual first, as they usually provide preliminary valve size recommendations based on the combustion head's flow resistance.
When selecting the size (nominal diameter) of a burner valve train, the primary criteria are the burner's maximum gas consumption and the gas supply pressure of the pipeline network. An undersized valve train restricts gas flow, impairing combustion output, while an oversized one reduces regulation precision or causes sluggish response times during opening and closing. Specific selection involves the following three steps:
1. Determine three key parameters: Before selection, the following data must be confirmed:
Rated/Maximum thermal load (Q): The burner's maximum output power, expressed in kW or kcal/h.
Lower heating value of the gas (H): For natural gas, this is typically 8,500–9,000 kcal/Nm³ or 35.6–37.7 MJ/Nm³.
Gas pressure upstream (P₁) and rated pressure downstream (P₂) of the valve: Determine whether the supply pressure is low (e.g., 2 kPa–5 kPa) or medium-to-high (e.g., 10 kPa–100 kPa).
2. Calculate maximum gas flow rate
Based on the thermal load and heating value, calculate the maximum standard flow rate ($V_{\max}$, in Nm³/h) required for the burner at full load: $V_{\max} = \frac{Q}{H}$
3. Consult selection charts based on flow rate and pressure differential ($K_v$ value method)
The core of valve train selection is its flow capacity ($K_v$ value). The $K_v$ value represents the flow rate of water passing through the valve when fully open with a 1-bar pressure differential across it. Since gas flow calculations are complex, practical guidelines are typically used:
Determine allowable pressure loss: The permissible pressure drop across the valve train is generally 10%–20% of the upstream pressure. The smaller the pressure drop, the larger the required valve train size.
Consult manufacturer specifications: Major burner or valve train brands (such as Dungs, Honeywell, etc.) provide charts correlating flow rate with pressure loss. After calculating \(V_{\max}\), locate the flow rate on the horizontal axis and the corresponding pressure on the vertical axis of the chart based on the available upstream pressure; the curve at the intersection point indicates the recommended valve size.
Quick Reference for Common Valve Sizes (Natural Gas, Supply Pressure approx. 2–3 kPa)
< 100 kW (Small units): Typically Rp 1/2" to Rp 3/4" (DN15–DN20)
100 kW – 350 kW: Typically Rp 1" to Rp 1 1/2" (DN25–DN40)
350 kW – 800 kW: Typically Rp 2" or DN50
800 kW – 2000 kW: Typically DN65 to DN80
> 2000 kW: Typically requires a flanged valve train of DN100 or larger, matched to the specific pressure drop.
Selection Considerations
1. Valve Train Configuration: High-capacity burners (typically > 1200 kW) are required by standards to be equipped with a Valve Proving System (VPS) to ensure no gas leakage when valves are closed; verify whether the valve train includes this feature or has a designated interface for it.
2. Gas Type: If using Liquefied Petroleum Gas (LPG) or town gas, the required \(K_{v}\) value and valve size will differ from those for natural gas due to variations in calorific value and density.
3. Follow Burner Manufacturer's Instructions: It is recommended to consult the burner manufacturer's technical manual first, as they usually provide preliminary valve size recommendations based on the combustion head's flow resistance.