Gas Pipe Size
AS/NZS 5601.2:2020 Clause 5.1.2
To ensure safe and efficient operation of gas appliances, piping between the cylinder regulator and appliance inlets must be of a suitable size to ensure that the operation of appliances is not compromised by the pressure drop in any pipe.
The pressure drop across the piping, with all appliances in operation, must not exceed 0.25kPa drop (at nominal burner pressure). Refer clause 5.1.2.
Why does this matter?
Insufficient pipe size will reduce gas pressure to the appliance, due to pipe wall friction. This results in poor combustion, dangerous emissions and ultimately appliance shutdown.
Gas Technical Regulators in some jurisdictions have identified concerns with the pipe size in some Recreational Vehicles and have reinforced that the diameter of gas pipes should be checked. There has been at least one case of penalty notices being issued on this matter, with rectification action required on in-service vehicles to resolve field issues.
Background
The gas consumption of recreational vehicles is dependent on the number of gas-burning appliances and their gas consumption. Over time, the number of appliances offered in Recreational Vehicles has increased, as has the consumption of many of those appliances.
For example, a vehicle with a continuous water heater, gas air heater, oven with cooktop and a couple of bayonet fittings could have an overall gas consumption of 160Mj/h (give or take). In a vehicle with a main run of 6 or 7m length and the common pipe size, this will be likely to have a pressure drop that exceeds the 0.25kPa limit.
How do I check my installation?
The pressure drop across the system should be checked by a pressure test. This is not a difficult test and is the only way to confidently confirm that your system is performing as required. In the event of a visit from a gas inspector, the results of this pressure test would be expected to be available.
Pressure test points are required to be provided at the outlet of gas pressure regulators and at the inlet of a gas appliance (or incorporated within the gas appliance). Refer AS/NZS 5601.2, clause 5.1.7. These test points are used to measure the pressure drop, with appliances operating at a nominal burner pressure.
The pressure drop test can be conducted on one vehicle, as a representative sample. However, in selecting your test vehicle be sure to consider your full range of vehicle options, as the test sample should be the “worst case” scenario – the vehicle with the most gas-burning appliances and/or the longest pipe runs. Alternatively, it may be necessary to conduct tests on several samples to adequately represent your product range.
What do I do if the pressure drop is too high?
If the measured pressure drop exceeds 0.25kPa, refer to Appendix C of AS/NZS 5601.2. This is an informative appendix to assist your gasfitter, engineer or designer with calculating the correct pipe size, based on the length of your piping run and the Mj/h gas consumption of the fitted appliances.
The charts and tables provided in Appendix C are based on accepted engineering calculation methods for pipe wall friction and can be used as a guide for determining the correct pipe size for each piping branch of the installation.
Note that there are 2 methods for calculation provided – one using graphs and another using tables. Choose the method that you are most comfortable with.
In order to correctly apply the calculations of Appendix C, you need to know the Mj/h consumption of each fitted appliance (including an allowance for a gas bayonet) and the length of the piping run and branches to each appliance. Follow the method shown in the worked examples with your measurements to assess your particular installation.
Once you have made any necessary changes to the pipe size in your installation, repeat the pressure drop test to confirm that you meet the requirements of clause 5.1.2, and hold the test reports as evidence.