Sizing Excess Flow Control Valves For Multilayer Gas Installations

 

We have received lots of calls regarding excess flow control valves since the transition period ended on 30 March 2023.

AS/NZS 5601.1:2022 - Clause 5.2.11 – Provision for fire emergency isolation for multilayer pipe.

Here is a guide to size the excess flow controls valves for multilayer pipe installations in Class 1a buildings only. (Please consult AS/NZS 5601.1:2022 for different class buildings).

We have identified that under certain conditions, multiple excess flow control valves may be required on an installation.

This is because the maximum flow through smaller branch lines might not generate a high enough flow of gas to close the large excess flow valve located at the meter or gas regulator.

Below is an example:

A common installation here in Queensland would be an LPG installation with a Continuous Flow Hot Water Unit and a Cooktop.

For ease we will say the hot water unit is 200 MJ/hr and the cooktop is 50 MJ/hr.

Total load for the system is 250 MJ/hr.

 

 

Looking at the excess flow valve sizing chart for LPG above, the system load is 250 MJ/hr and we have more than one appliance.

GS.6 would be the choice of valve.

This valve will be sufficient for installations up to 374 MJ/hr and the valve will close at 5.7 m3/hr max gas flow.

Excess flow valves will generally shut off at 30-45% above nominal flow.

Nominal flow of the GS.6 is 3.9 m3/hr. 3.9 + 30% = 5.07 m3/hr.

Closing flow rates – 5.07-5.70m3/hr.

 

 

Using the multilayer pipe sizing chart above, we can size the pipe runs on the drawing:

If we look at pipe run A-B, we need to run 10 metres supplying 250MJ/hr.

The sizing chart for 10 metres shows that 26mm pipe would provide the MJ needed for the system (389 mj/hr).

We now need to figure out how much gas can flow through that pipe.

The sizing chart tells us that 389 mj/hr is the capacity for this section of pipe for an LPG system providing 2.75 kPa of LPG.

To find the gas flow in cubic metres per hour, we will need to divide the megajoule capacity of the pipe by the heat value of the gas. (Remember LPG is 96 mj/m3 and Natural gas is 38 mj/m3)

389 MJ/hr divided by the heat value of LPG (96) = 4.05 m3/hr.

Please note, this figure is the volume of gas that could travel through an orifice or injector at 2.75 kPa.

If a fire broke out and melted the pipe, we would be dealing with an open end. The open end would discharge the gas at a much greater volume than 4.05 m3/hr.

If we look at a 26mm multilayer pipe with the internal diameter of 20mm.

If we assumed the injector was 5mm, we could double or triple the figure of 4.05 m3/hr to give us a rough idea of the Volumatic flow through an open end.

4.05 x 3 = 12.05 m3/hr through an open end.

The GS6 excess flow control valve that we selected will shut off at 5.07 m3/hr of gas flow.

This Volumatic gas flow calculation used is for guidance purposes only.

In order to work out the exact Volumatic flow of an open-ended pipe, you will need to use the Spitzglass formula.  

We have established that we can install a GS6 valve at the gas regulator in order to shut down the gas supply in the event of a fire.

We need to consider the rest of the system. We have only confirmed the 10 metre pipe run from sections A-B on the diagram.

Section B-C is 2 metres of pipe work supplying 200 mj/hr.

We could run this section of pipe down to 20mm as the nominal connection to the continuous flow hot water system is 20mm.

20mm for 2 metres can supply 408 mj/hr divided by 96 = 4.35 m3/gas through an injector.

4.35 x 3 = 13.05 m3/hr of gas though a rupture or open end.

If this pipe ruptured, it would easily exceed the shut off pressure of 5.07 m3/hr.

For pipe run B-D supplying 50 mj/hr over a 5 metre run, we could use 16mm pipe capable of supplying 137 MJ/hr (6 metres).

137 mj/hr divided by 96 = 1.42 m3/hr (through an injector).

1.42 x 3 = 4.28 m3/hr though an open-ended pipe.

This wouldn’t close off our GS6 excess flow control valve at the regulator.

On a new installation, we could simply upsize this section of pipework to increase the Volumatic flow.

If it was a 20mm pipe, capable of supplying 219 mj/hr, an open end would be approximately 6.8 m3/hr.

With a 20mm pipe feeding the cooktop, we can install just one excess flow control valve on this system.

If we wanted to run 16mm pipe or this was an existing system, we would need to install an additional excess flow valve. This would ensure that if a fire compromised the 16mm pipe, it would still shut down the gas supply.

We would need to install another excess flow control valve at the tee feeding the cooktop:

 

The illustration above shows the two excess control valves installed on this multilayer pipe installation.

If a fire was to break out in any section of the house, we know that the gas supply would be shut down if any section of pipe is compromised. What other options do we have?

Run all branch lines in copper – The main run can go in multi-layer pipe but the branch lines will all run in copper. This may also make it easier to comply with Clause 4.2 (table 4.2 and 5.6.12) – which prohibits brazing within one meter of a joint with non-metallic components.

The other option would be to install the whole system in copper pipework.

The options are possible with a new installation but when we are retrofitting these valves to existing multilayer pipe systems, we may need to consider the use of multiple valves to comply with Clause 5.2.11 in AS/NZS 5601.1:2022.

This is a guide and uses some assumptions to calculate Volumatic flow rates.

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This article has been updated on 17 August 2023. For further information, please contact the Technical team at MPAQ.

Photo features the SENTRY GS Excess Flow Valve from Maxitrol