Over-Pressure Shut-Off Valve
The LPG in your tank / cylinders is stored at a pressure of 8 bar.
LPG has a high calorific value, and the pressure required for use is much, much lower at 37 millibar (mbar).
A regulator is used to take the 8 bar pressure that your LPG / cylinder holds, and bring the gas pressure down to 37 mbar, which is your appliances run at.
If the regulator should fail the full eight bar of pressure could be transmitted to the appliances, potentially resulting in a fireball.
To prevent this an OPSO (Over-Pressure Shut-Off valve) is built into your changeover valve, which will trip out if the regulator should fail.
If the OPSO valve trips out and needs a reset, contact your catering engineer as the cause of the ‘trip’ needs to be investigated and rectified, before the flow is restarted.
Tower insists that an OPSO valve is the minimum requirement for a mobile catering unit, based on this information.
Note: Image courtesy of https://www.bes.co.uk