Dummy valves in general used as low cost and run
1-)initially in a system will produce natural flowing for a certain long time / then later replaced with active valves allready designed initially and spaced but replaced temporary with dummies
2-)used when you get wash out for mandrel holes and less cost than pst valve or get cut for pst rubber
3-) used when you replace your turbine with higher discharge gas pressure, so a selective valves in system will be replaced with dummies and other will replace with higher setting pressure
4-) in some cases upper valves suffering from reopening problem as the people try deepining p.o.i and not care with design operating pressure, so upper valves reopening and they solve this problem by replacing upper valves with dummies to avoid drop in production or circulating lift gas.
AMI