A customer approached HDL because they had a gas manifold that draws gas from one back of cylinders and they wanted it to automatically swap to the second bank once the first bank was depleted. Once the first bank was re-filled, it would automatically swap back once the second was depleted. This problem is complicated further by the regulators drifting by about half a bar as the banks became depleted and a further half a bar when the flow through them was increased.
This problem was to be solved using the most low-cost but reliable solution.
Traditional solutions to this problem include pressure switches / transducers combined with solenoid valves or a handle on one of the regulators to physically turn up and down the set point to determine the active bank. Neither of these solutions were acceptable to the customer.
HDL proposed a solution with a single stage regulator on each cylinder to drop the bottle pressure to ~10 bar. This was to be fed into either side of a shuttle valve; however, those shuttle valves on the market simply change side with the presence of a differential pressure and even if the regulators were perfectly balanced, as soon as there was any flow through them, the pressure dropped and the valves changed sides. Differential pressure shuttle valves are available on the market, but at a high price.
Thus, HDL designed and manufactured a shuttle valve that would only shuttle at a set differential pressure, in this case 2 bar. All of the movement of the regulators with varying flow and bottle content did not result in a shuttle, but as the bottles became empty, and the regulator output fell below 8 bar and the system automatically shuttled to the full bank. Although not requested by the customer, provision was made so that a position switch could be included to provide alerts to the end user that a bank had become depleted.