Why choose Medem differential pressure proving?

The differential gas pressure proving method as developed and patented by Medem operates by measuring the pressure differentially across the inlet and the outlet of a gas isolation valve using micro transducers. All other systems can only see the gas pressure when the valve is open.

1. Differential proving enables the supply pressure to be measured before the associated isolation valve is opened. This means that in the event of gas over pressure or under pressure the valve would remain safely shut and reported on the system LCD. Therefore only the differential gas pressure proving method can be considered to be truly fail safe.

2. This method is dynamic in that it takes into account any supply pressure changes that could be temporarily created by increased demand such as a boiler firing. Such transient changes in pressure would have the potential to cause other methods to isolate the gas supply needlessly.

3. Some other gas pressure proving methods can fail to identify a gas leak because they have to be set on installation and if the supply pressure at the time of setting is even slightly higher than in subsequent use then a leak can be missed during test.

When gas is required, the pressure proving test is completed by the following steps.

• Checks for adequate incoming upstream gas pressure, if gas pressure is low the test will not start and a ‘low gas pressure message will be displayed’ this is to reduce the potential of flames being extinguished at low pressure or appliances locking out. This is a dynamic check and would be monitored for at all times even when gas is live and being used.
  
  
• If there is adequate upstream gas pressure, the solenoid valve will be opened to allow for filling the downstream gas pipework. ‘Fill Time’
  
  
• After the ‘fill time’ the gas solenoid valve will close, and the ‘Prove Time’ begins. During the ‘Prove Time’ the downstream pressure will be dynamically compared to the upstream pressure, if a drop in downstream gas pressure is identified and the differential is reached a ‘Test Fail’ alarm will be raised and the gas will remain isolated.
   
• If during the ‘Prove Time’ the gas pressures remain the same the panel will open the valve and make ‘Gas Available for Use’ –

The fill and prove times are adjusted during commissioning.