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View of the Lp Gas Stage

Richard Smith, technical regulators sales manager at Clesse (UK) Ltd, asks if we really need three-stage pressure reduction.

Views on whether we really need to drop our transmission pressures to 75mbar vary between lpg gas companies but, in the light of the Gill report, we should all be thinking about the way we supply lp gas.

As a regulator manufacturer, Clesse UK had to decide where best to target its development efforts. Being an innovative company, it has developed both 750mbar and 75mbar distribution methods so they are as similar as possible. Each option has its advantages and disadvantages but, through creative thinking, Clesse has developed reliable installation kits for all applications.

Clesse UK has spent a lot of time and effort ensuring that its equipment complies fully with EN13785 and is reliable enough to ‘fit and forget’, and has launched a new version of its BP2203 regulator, the BP2203FC, for use within second stage meter boxes.

With two-stage systems, vessel pressure is typically reduced to 750mbar, which is then transmitted through PE pipe to the property. It is then reduced further to 37mbar using a regulator installed outside the property that has under and over pressure protection.

The advantages of a two-stage system are that distribution pipework and regulators can be smaller, and pressure loss can be ‘disguised’ by increasing the first stage pressure setting. The disadvantages are that any lp gas escape could be large and potentially hazardous, re-liquefication can sometimes occur if pressures above 2 bar are set at the first stage, and pipework is recommended to be 3m from the property.

Clesse is currently developing a new third stage regulator to use within third stage meter boxes that have a manual UPSO reset. Third stage regulators have a lower pressure differential to cope with – 75mbar down to 37mbar. This means that it takes a lot more ‘effort’ for the lpg gas to squeeze through the regulator orifice.

Subsequently, the regulator has to be physically larger than a standard second stage unit. However, Clesse has developed the 2402L balanced orifice regulator, which can pass 25kg/hr (350kW/hr) of propane with ease.

The three-stage system reduces pressure at the lpg bulk vessel to 75mbar for transmission, which is then reduced to 37mbar at the property. This regulator has to have UPSO and could be installed within the building, although this is not recommended.

The advantages of a three-stage system include bringing lpg into the same distribution format as natural gas; lower distribution pressures, which means any potential leakage could result in less lp gas being released, and the customer only having an UPSO to reset on the regulator, which avoids confusion. Pipework can also be less than 1m from the property, and compact, ‘close coupled’ vessel pressure to 75mbar regulators can be used on the bulk vessel, which stops the customer going near the vessel and potentially incorrectly resetting the OPSO if the lp gas runs out.

The disadvantages of a three-stage system are that often larger PE pipework is required due to lower distribution pressure, PE pipework over 63mm requires specialist installers, and there’s another pressure control valve to buy/fit/break/be interfered with.

Lp gas companies need to set their own standards on where and when to use a two or three-stage system. The maximum capacity required at the appliance has to be taken into consideration in deciding whether a third stage regulator will either a) pass the capacity, or b) be physically too large for the installation. There is no doubt that a three-stage system is safer if pipework is at risk of being damaged, but then we have been using the two-stage system for the last 50 years!

The question has to be asked – which system is best? The answer depends on the individual installation, risk assessment and proximity to habitable buildings.

An amendment to UKLPG Code of Practice 22 will be issued soon, which will try to bring lpg systems in line with the natural gas marketplace. However, as lp gas has different properties to natural gas, Clesse is developing tailored lpg gas technology to operate in the same environment as our natural gas colleagues. Although it won’t be mandatory, it will strongly suggest that the three-stage system be favoured.

Whatever your preference, Clesse UK can supply a system of lp gas control equipment to enable you to operate an efficient and effective lpg gas supply system from any bulk vessel to any lpg equipment.

Contact Clesse (UK) Ltd on 07825 641786 www.clesse.co.uk

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