The difference between PTC's Safelift (TM) valves and their traditional counterparts is the result of a completely fresh look at valve design.
The Safelift (TM) valves are essentially modular. All valves in the family incorporate the same check valve module. These were designed using computational fluid dynamics to ensure the check valve flow paths and the opening dimensions were optimised with respect to erosion across the metal/metal seal faces. The orifice or gas lift valve choke also moves with the check valve as it opens, which significantly reduces chattering. Finally, the check valve spring location (around the dart) and size allows for it to be more robust than on traditional valves, requiring an opening pressure differential across the valve orifice of 25 psi.
In a traditional gas lift check valve design, the flow stream usually impinges directly on check valve seal face, which is usually held in place using a relatively lightweight spring and valve movement is relatively small. As a result, erosive velocities across the valve seal faces are high and the valves have a tendency to chatter. Both of these conditions result in premature seal failure. The Safelift (TM) check valve design addresses all these shortcomings and as a result valve performance, reliability and longevity is far superior.
In addition to the check valve module, the Safelift (TM) injection pressure operated (IPO) unloading valves employ a unique, bellows unloading valve module. The bellows employed are rated to 10k psi (facilitating very deep gas lift valve deployment), but despite this high pressure rating the bellows are much less stiff than traditional bellows and facilitate unusually long valve stem travel. Also unlike traditional valves, the bellows function is not to provide the force to hold the valve closed on its seat. Instead, in the Safelift valve a spring is used to hold the valve closed ( the bellows function is just to retract the valve off seat). Consequently in the event of dome pressure loss or bellows failure, the unloading valve is uniquely designed to fail-safe in the closed position. In any case, since the valves employ metal/metal seal N2 domes and pressure balanced edge welded bellows the likelihood of dome pressure loss in Safelift valves is low.
The Safelift bellows OD is also larger than that used in traditional gas lift valves and as a result the valves are less sensitive to tubing pressure variations. The unusually long bellows travel also means the valve suffers very little from throttling and the unloader module is essentially invisible to flow when fully open. Consequently, shallow-set Safelift (TM) IPO unloading valves are now confidently being used for long term gas lifting (essentially as a backup operating valve for cases where operating conditions unexpectedly change) without concerns of accelerated time to failure.
