"UDT MAKE" 'AN' Series Valves are charged with nitrogen pressure acting on the bellows. This determines the set pressure of the valve. Nitrogen charged valves are primarily sensitive to casing pressure. The valve is open when the combination of pressures supplied by the casing and tubing exceed the dome pressure. As the casing pressure declines to the valve set pressure, the gas lift valve closes. Since the casing pressure controls the valve operation, the nitrogen charge is reduced in each lower valve to avoid interference with the upper valves. All UDT Series Valves are suitable for either continuous, flow or intermittent lift wells.

Sources:- https://www.udtltd.com/11-Conventional%20Casing%20pressure%20Operated%20Gas%20Lift%20Valves.html

United Drilling Tools Limited

India-based United Drilling Tools Ltd is one of the leading manufacturers of high-quality products used in the upstream operations. UDT is widely recognized for manufacturing downhole tools, wireline & well service equipment, gas lift equipment, and large OD casing connectors. UDT's products are manufactured to the standard equipment or are customized to the client's particular specifications. The firm has an excellent track record of supplying products with the most reliable designs and staying consistent with competitive prices.